59 results on '"Zoë R. Turner"'
Search Results
2. Bimolecular Reductive Elimination of Ethane from Pyridine(diimine) Iron Methyl Complexes: Mechanism, Electronic Structure, and Entry into [2+2] Cycloaddition Catalysis
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Carli B. Kovel, Jonathan M. Darmon, S. Chantal E. Stieber, Gisselle Pombar, Tyler P. Pabst, Bastian Theis, Zoë R. Turner, Ökten Üngör, Michael Shatruk, Serena DeBeer, and Paul J. Chirik
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Colloid and Surface Chemistry ,General Chemistry ,Biochemistry ,Catalysis - Published
- 2023
3. Zirconium permethylpentalene amidinate complexes: characterization, bonding, and olefin polymerization catalysis
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Thomas P. Robinson, Maureen Georges, Zoë R. Turner, Jean-Charles Buffet, and Dermot O’Hare
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Inorganic Chemistry ,Organic Chemistry ,Physical and Theoretical Chemistry - Abstract
The synthesis and characterization of new zirconium permethylpentalene (form)amidinate complexes are described: Pn*Zr{N(Dipp)2CH}Cl (1), Pn* = η8-C8Me6 and Dipp = 2,6-iPr-C6H3; [Pn*Zr{N(p-tol)2CH}Cl]2 (2), p-tol = 4-Me-C6H4; [Pn*Zr{N(iPr)2CMe}Cl]2 (3); Pn*Zr{N(iPr)2CPh}Cl (4); Pn*Zr{N(4-Me-C6H4)2CH}2 (5); [Pn*Zr{N(iPr)2CCH2}]2 (6); and Pn*Zr{N(iPr)2CPh}(O-2,6,-Me-C6H3) (7). The monohalide derivatives 1–4 demonstrate considerable structural diversity as the nature of the (form)amidinate-supporting ligand is changed. While complexes with acidic backbone protons proved susceptible to deprotonation using mild bases, those without underwent straightforward salt metathesis reactions with alkali metal salts, leading to complexes [Pn*Zr{N(iPr)2CCH2}]2 (6) and Pn*Zr{N(iPr)2CPh}(O-2,6-Me-C6H3) (7). Preliminary slurry-phase ethylene polymerization studies are also reported using complexes 2, 4, 5, and 7 to gain a direct comparison to the highly active, yet electronically saturated, Pn*Zr(CpR)Cl catalyst family.
- Published
- 2022
4. Multimetallic permethylpentalene hydride complexes
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Duncan A. X. Fraser, Zoë R. Turner, Robert T. Cooper, Jean-Charles Buffet, Jennifer C. Green, and Dermot O’Hare
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Inorganic Chemistry ,Physical and Theoretical Chemistry - Abstract
The synthesis and characterization of group 4 permethylpentalene (Pn* = C8Me6) hydride complexes are explored; in all cases, multimetallic hydride clusters were obtained. Group 4 lithium metal hydride clusters were obtained when reacting the metal dihalides with hydride transfer reagents such as LiAlH4, and these species featured an unusual hexagonal bipyramidal structural motif. Only the zirconium analogue was found to undergo hydride exchange in the presence of deuterium. In contrast, a trimetallic titanium hydride cluster was isolated on reaction of the titanium dialkyl with hydrogen. This diamagnetic, mixed valence species was characterized in the solid state, as well as by solution electron paramagnetic resonance and nuclear magnetic resonance spectroscopy. The structure was further probed and corroborated by density functional theory calculations, which illustrated the formation of a metal-cluster bonding orbital responsible for the diamagnetism of the complex. These permethylpentalene hydride complexes have divergent structural motifs and reactivity in comparison with related classical cyclopentadienyl analogues.
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- 2022
5. Tuning polyethylene molecular weight distributions using catalyst support composition
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Philip Kenyon, D. W. Justin Leung, Zoë R. Turner, Jean-Charles Buffet, and Dermot O’Hare
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Inorganic Chemistry ,Polymers and Plastics ,Organic Chemistry ,Materials Chemistry - Abstract
Bimodal polyethylene is generated from a single immobilized catalyst on a single support under a single set of reaction conditions without introducing chain transfer agents. Using rac-ethylenebis(1-indenyl)zirconium dichloride [(EBI)ZrCl2] immobilized on a nickel-containing layered double hydroxide (LDH) support produces two distinct molecular weight distributions. The ratio of these two distinct fractions can be tuned by varying the LDH support as well as by changing the reaction conditions.
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- 2022
6. CO2 activation by permethylpentalene amido zirconium complexes
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Jean-Charles Buffet, Zoë R. Turner, Elizabeth A. Hamilton, Dermot O'Hare, Alexander F. R. Kilpatrick, and Duncan A. X. Fraser
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Inorganic Chemistry ,chemistry.chemical_compound ,Zirconium ,Cyclopentadienyl complex ,chemistry ,Carbon dioxide ,Polymer chemistry ,chemistry.chemical_element ,Reactivity (chemistry) - Abstract
We report the synthesis and characterisation of new permethylpentalene zirconium bis(amido) and permethylpentalene zirconium cyclopentadienyl mono(amido) complexes, and their reactivity with carbon dioxide.
- Published
- 2021
7. Ethylene Polymerization Using Zirconocenes Supported on Pentafluorophenyl-Modified Solid Polymethylaluminoxane
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Jean-Charles Buffet, Zoë R. Turner, Dermot O'Hare, and Jessica V. Lamb
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Inorganic Chemistry ,Polymers and Plastics ,Ethylene polymerization ,Chemistry ,Organic Chemistry ,Polymer chemistry ,Materials Chemistry ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,0210 nano-technology ,01 natural sciences ,0104 chemical sciences - Abstract
Three permethylindenyl zirconocenes have been supported on a hexane-insoluble form of polymethylaluminoxane modified with 40 wt % pentafluorophenol (sMAO(PFP)). The solid precatalysts were characterized by solid-state nuclear magnetic resonance spectroscopy, and their ethylene polymerization activity was studied. When supported on sMAO(PFP), Me2SB(Cp,I*)ZrX2 ({(η5-C9Me6)Me2Si(η5-C5H4)}ZrX2; X = Cl, CH2Ph, and Me) showed ethylene polymerization activities up to 25% higher than when supported on unmodified sMAO with the same [Al]0/[Zr]0 catalyst loading: activities of 6454 and 5144 kgPE molZr–1 h–1 bar–1 at 80 °C for Me2SB(Cp,I*)ZrCl2 supported on sMAO(PFP) and sMAO, respectively. The systems produced relatively low-molecular weight polyethylenes (Mw < 170 kg mol–1 at 80 °C) with minimal defects and branching. The polymers showed good flowability, although they displayed more aggregated morphologies than polyethylenes produced from unmodified sMAO. On increasing the solvent volume fivefold, the activity and polymer molecular weights approximately doubled.
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- 2020
8. Physicochemical surface-structure studies of highly active zirconocene polymerisation catalysts on solid polymethylaluminoxane activating supports
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Nicholas H. Rees, Zoë R. Turner, Jean-Charles Buffet, Dermot O'Hare, and Alexander F. R. Kilpatrick
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NMR spectra database ,chemistry.chemical_compound ,Polymerization ,chemistry ,Solid-state nuclear magnetic resonance ,Polymer chemistry ,Materials Chemistry ,Cationic polymerization ,General Materials Science ,Diffuse reflection ,Metallocene ,Aluminoxane ,Catalysis - Abstract
Physicochemical surface-structure studies of highly active slurry-phase ethylene polymerisation catalysts has been performed. Zirconocene complexes immobilised on solid polymethylaluminoxane (sMAO) (sMAO–Cp2ZrX2), have been investigated using SEM-EDX, diffuse reflectance FT-IR (DRIFT) and high field (21.1 T) solid state NMR (ssNMR) spectroscopy. The data suggest a common surface-bound cationic methylzirconocene is the catalytically active species. 91Zr solid sate NMR spectra of sMAO–Cp2ZrCl2 and sMAO–Cp2ZrMe2 are consistent with a common surface-bound Zr environment. However, variation of the σ-donor (X) groups on the metallocene precatalyst leads to significant differences in polymerisation activity. We report evidence for X group transfer from the precatalyst complex onto the surface of the aluminoxane support, which in the case of X = C6F5, results in a 38% increase in activity.
- Published
- 2020
9. Controlling the activity of an immobilised molecular catalyst by Lewis acidity tuning of the support
- Author
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Zoë R. Turner, Meng Lyu, Dermot O'Hare, Chunping Chen, Philip Kenyon, D. W. Justin Leung, and Jean-Charles Buffet
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Layered double hydroxides ,chemistry.chemical_element ,Zinc ,engineering.material ,Post-metallocene catalyst ,Catalysis ,Chemical engineering ,chemistry ,Phase (matter) ,Slurry ,engineering ,Physical and Theoretical Chemistry ,Support surface ,Chemical composition - Abstract
The performance profile of a supported metallocene catalyst in slurry-phase ethylene polymerisation can be significantly enhanced by tuning the chemical composition of the support. By employing catalyst supports derived from zinc-containing layered double hydroxides (LDHs), the slurry phase ethylene polymerisation productivity of (EBI)ZrCl2 (EBI = rac-ethylenebis(indenyl)) can be quadrupled relative to a magnesium-containing support. Productivity increases approximately linearly with zinc content of the LDH before reaching a plateau; our experiments suggest the productivity of this catalyst system is related to the overall Lewis acidity of the support surface. We have found that iron-containing LDH supports with a similar overall Lewis acidity also result in productivity enhancements, demonstrating the general nature of this phenomena.
- Published
- 2021
10. Supported permethylindenyl titanium catalysts for the synthesis of disentangled ultra-high molecular weight polyethylene (disUHMWPE)
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Jean-Charles Buffet, Dermot O'Hare, Clement G. Collins Rice, and Zoë R. Turner
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Ultra-high-molecular-weight polyethylene ,Materials science ,Metals and Alloys ,chemistry.chemical_element ,General Chemistry ,Polyethylene ,Catalysis ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,Chemical engineering ,chemistry ,Ethylene polymerization ,Materials Chemistry ,Ceramics and Composites ,Titanium - Abstract
Novel permethylindenyl-phenoxide (PHENI*)ansa-metallocene titanium complexes have been synthesised and immobilised on inorganic solid supports to afford highly effective catalysts for slurry-phase ethylene polymerisation. When supported on solid polymethylaluminoxane these complexes were both extremely active (up to 3.7 × 106gPEmolTi−1h−1bar−1) and produced substantially disentangled polyethylene with a weight-average molecular weight (Mw) of 3.4 MDa (disUHMWPE).
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- 2021
11. Metallocene polyethylene wax synthesis
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Tossapol Khamnaen, Zoë R. Turner, Dermot O'Hare, Jessica V. Lamb, and Jean-Charles Buffet
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Materials science ,Polymers and Plastics ,Organic Chemistry ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,POLYETHYLENE WAX ,Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,Polymer chemistry ,Materials Chemistry ,0210 nano-technology ,Metallocene - Abstract
Solid polymethylaluminoxane (sMAO) supported ansa-bridged permethylindenyl zirconocenes Me2SB(CpR,I*)ZrX2 ({(η5-C9Me6)Me2Si(η5-C5H3R)}ZrX2; R = H, Me, and nBu; X = Cl, Br, Me, and CH2Ph) have been investigated as catalysts for the slurry-phase polymerization of ethylene in the presence of H2. The catalysts demonstrated remarkable stability to H2 both in a high-throughput screening system and in a 2 L batch reactor, with an almost constant ethylene uptake maintained throughout the polymerization runs. The catalysts demonstrated very high ethylene polymerization activities, almost 3 times higher than sMAO-(CpnBu)2ZrCl2 (industrial standard zirconocene catalyst) under the same conditions. The presence of small quantities of H2 (
- Published
- 2021
12. Synthesis, characterisation and slurry phase ethylene polymerisation of rac-(PhBBI*)ZrCl2 immobilised on modified layered double hydroxides
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Alexander F. R. Kilpatrick, Christopher M. R. Wright, Zoë R. Turner, Dermot O'Hare, Jean-Charles Buffet, and Grace E. Hickman
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Zirconium ,Ethylene ,010405 organic chemistry ,Process Chemistry and Technology ,Layered double hydroxides ,Methylaluminoxane ,chemistry.chemical_element ,engineering.material ,010402 general chemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Polymerization ,Phase (matter) ,Polymer chemistry ,engineering ,Physical and Theoretical Chemistry ,Metallocene - Abstract
Rac- and meso-bis(1-hexamethylindenyl)phenylborane zirconium dichloride, {rac-, meso-( Ph BBI*)ZrCl 2 } has been synthesised and fully characterised. The slurry phase ethylene polymerisation performance of rac-( Ph BBI*)ZrCl 2 immobilised on a range of methylaluminoxane (MAO)-modified, solvent-dispersed, high surface area layered double hydroxides (AMO/AIM-Mg x Al-CO 3 LDHs) have been studied. The polymerisation activities show a strong dependence on the nature of the LDH. Rac-( Ph BBI*)ZrCl 2 supported on a MAO-modified 1-hexanol dispersed [Mg 0.73 Al 0.27 (OH) 2 ][CO 3 ] 0.135 LDH displayed a maximum ethylene polymerisation activity of 6641 kg PE mol Zr−1 h −1 bar −1 at 70 °C and 2 bar ethylene. Benchmarking studies reveal that some of the rac-( Ph BBI*)ZrCl 2 supported catalysts outperform a range of commonly used industrial metallocene PE catalysts.
- Published
- 2019
13. Ring-opening polymerisation of l- and rac-lactide using group 4 permethylpentalene aryloxides and alkoxides
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Dermot O′Hare, Thomas P. Robinson, Jessica V. Lamb, Dipa Mandal, Zoë R. Turner, and Jean-Charles Buffet
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Inorganic Chemistry ,chemistry.chemical_classification ,chemistry.chemical_compound ,Lactide ,chemistry ,Polylactic acid ,Polymerization ,Tacticity ,Alkoxide ,Polymer chemistry ,Nuclear magnetic resonance spectroscopy ,Polymer ,Ring (chemistry) - Abstract
A new family of group 4 permethylpentalene (C8Me62−; Pn*) aryloxide and alkoxide complexes have been synthesised and fully characterised by multinuclear NMR spectroscopy and single-crystal X-ray diffraction; (η8-C8Me6)Zr(OR)2(R =tBu (1), 2,6-Me-C6H3(2), 2,6-iPr-C6H3(3) and 4-OMe-C6H4(4)), (η8-C8Me6)Zr (OR) (R = 2,6-tBu-C6H3(5) and 2,6-tBu-4-Me-C6H2(6)), (η8-C8Me6)ZrCp(OR) (R =tBu (7), 2,6-Me-C6H3(8) and 2,6-iPr-C6H3(9)), (η8-C8Me6)TiCp(O-2,6-Me-C6H3) (10) and (η8-C8Me6)ZrCpMe(OR) (R = 2,6-Me-C6H3(11), 2,6-iPr-C6H3(12) and 2,4-tBu-C6H3(13)).2,3,6,7,9,10and12were studied as initiators for the ring-opening polymerisation (ROP) ofL-lactide, and2,3,6,7and10were studied as initiators for the ROP ofrac-lactide.3was found to be the most active initiator for the ROP ofL-lactide (kobs= 0.35 h−1) and2for the ROP ofrac-lactide (kobs= 0.21 h−1). These initiators produced isotactic PLA for the ROP ofL-lactide and moderately heterotactic enriched (maximumProf 0.69) or atactic PLA for the ROP ofrac-lactide with polymer chains consisting of polylactic acid repeat units with –OR and –OH end groups.
- Published
- 2021
14. CO
- Author
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Elizabeth A, Hamilton, Alexander F R, Kilpatrick, Zoë R, Turner, Duncan A X, Fraser, Jean-Charles, Buffet, and Dermot, O'Hare
- Abstract
We report the synthesis and characterisation of new permethylpentalene zirconium bis(amido) and permethylpentalene zirconium cyclopentadienyl mono(amido) complexes, and their reactivity with carbon dioxide.
- Published
- 2021
15. Synthesis of zirconocene complexes and their use in slurry-phase polymerisation of ethylene
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Zoë R. Turner, Phakpoom Angpanitcharoen, Jessica V. Lamb, Dermot O'Hare, and Jean-Charles Buffet
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chemistry.chemical_compound ,Ethylene ,Polymerization ,Ethylene polymerization ,Chemistry ,General Chemical Engineering ,Phase (matter) ,Slurry ,General Chemistry ,High-density polyethylene ,Crystal structure ,Nuclear chemistry ,Catalysis - Abstract
A new family of zirconocene complexes of the type (3-RInd#)2ZrX2 (where Ind# = C6Me5H and R = Me, Et and Ph) have been synthesised and fully characterised. Six new crystal structures have been reported (meso-(3-EtInd#)2ZrBr2, rac-(3-EtInd#)2ZrCl2, rac-(3-EtInd#)2Zr(CH2Ph)2, meso-(3-EtInd#)2Zr(CH2Ph)2, meso-(3-MeInd#)2ZrBr2 and meso-(3-MeInd#)2Zr(CH2Ph)2). The complexes were studied for slurry-phase ethylene polymerisation when immobilised on solid polymethylaluminoxane (sMAO). Variation in the initiation group was found to have greater influence over polymerisation activity for meso-catalysts than rac-catalysts, with meso-alkyl catalysts showing higher polymerisation activities than meso-halide. Below 70 °C, polymerisation activity follows the order sMAO-meso-(3-EtInd#)2Zr(CH2Ph)2, sMAO-meso-(3-EtInd#)2ZrCl2 and sMAO-meso-(3-EtInd#)2ZrBr2 (activities of 657, 561, and 452 kgPE molM−1 h−1 bar−1, respectively). sMAO-meso-(3-EtInd#)2ZrBr2 produces HDPE with the highest molecular weight, followed by sMAO-meso-(3-EtInd#)2ZrCl2 and sMAO-meso-(3-EtInd#)2Zr(CH2Ph)2 (Mw of 503, 406, and 345 kg mol−1, respectively, at 50 °C). sMAO-meso-(3-MeInd#)2ZrBr2 produced HDPE with almost identical molecular weights to sMAO-meso-(3-EtInd#)2ZrCl2 (395 kg mol−1 at 50 °C).
- Published
- 2021
16. Polymethylaluminoxane organic frameworks (sMAOF) – highly active supports for slurry phase ethylene polymerisation
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Jean-Charles Buffet, Dermot O'Hare, Harry S. Geddes, Andrew L. Goodwin, Alexander F. R. Kilpatrick, and Zoë R. Turner
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Zirconium ,010405 organic chemistry ,Aryl ,chemistry.chemical_element ,010402 general chemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,Solid-state nuclear magnetic resonance ,chemistry ,Polymerization ,Phase (matter) ,Polymer chemistry ,Linker ,BET theory - Abstract
A series of modified solid polymethylaluminoxane (sMAO) catalyst supports have been developed for slurry phase ethylene polymerisation, using aryl di-ol modifier groups. Characterisation using ICP-MS analysis, X-ray total scattering, SEM–EDX, diffuse FT-IR and solid state NMR spectroscopy shows that the organic linker groups are uniformly distributed in a proposed organic framework stucture we call a “sMAOF”. When used as a support for rac-ethylene{bis(1-indenyl)} zirconium dichloride, (EBI)ZrCl2, these linker modified sMAOF materials provide a 40% enhancement in polymerisation activity with respect to unmodified sMAO: activities of 163 × 103 and 116 × 103 kgPE molZr−1 h−1 at 80 °C for (EBI)ZrCl2 supported on sMAOF(1,4-HO(C6F4)OH) and sMAO, respectively. The observed activity increase is correlated with the higher BET surface area and increased porosity in the linker modified sMAOF activating support.
- Published
- 2021
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17. Group 4 constrained geometry complexes for olefin (co)polymerisation
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Thomas J. Williams, Zoë R. Turner, Alexander D.H. Smith, Jean-Charles Buffet, and Dermot O'Hare
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chemistry.chemical_classification ,Olefin fiber ,Ethylene ,010405 organic chemistry ,Chemistry ,Process Chemistry and Technology ,Geometry ,Polymer ,010402 general chemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Styrene ,Metal ,chemistry.chemical_compound ,Polymerization ,Group (periodic table) ,visual_art ,visual_art.visual_art_medium ,Physical and Theoretical Chemistry - Abstract
We report the synthesis and characterisation of eight constrained geometry complexes, with variation of the amido fragment, ansa-bridge, permethylindenyl group, metal centre and initiator groups from the parent complex Me2SB(tBuN,I*)TiCl2. These complexes have been shown to be highly active for slurry-phase ethylene polymerisation when supported on solid polymethylaluminoxane (sMAO), with activities up to 7048 kgPE/molTi/h/bar. Ethylene/1-hexene and ethylene/styrene copolymerisations have shown these complexes to be good incorporators of comonomers into the polymer chain.
- Published
- 2020
18. Slurry-phase ethylene polymerisation using group 4 ansa-bridged permethylindenyl complexes supported on polymethylaluminoxane
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Dermot O'Hare, Jean-Charles Buffet, Jack E. McLaren, Jessica V. Lamb, Zoë R. Turner, and Joseph C. Abell
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chemistry.chemical_classification ,Dimethylsilane ,010405 organic chemistry ,Chemistry ,Process Chemistry and Technology ,Polymer ,010402 general chemistry ,Branching (polymer chemistry) ,01 natural sciences ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,Hydrocarbon ,Polymerization ,Polymer chemistry ,Hydroxide ,High-density polyethylene ,Physical and Theoretical Chemistry - Abstract
Five new group 4 ansa-bridged permethylindenyl complexes with either a dimethylsilane bridge or a tetramethyldisilane bridge have been synthesised and fully characterised. These complexes were supported on a hydrocarbon insoluble polymethylaluminoxane (sMAO) and their slurry-phase ethylene polymerisation performance was investigated. The highest activity was achieved using S B M e 2 (CpMe,I*)Zr(CH2SiMe3)2 (8042 kgPE molZr–1 h–1 bar–1 at 60 °C) but a decrease in activity was observed with an increase in the length of the bridge. DSC analysis of the polymers revealed the production of HDPE with minimal branching and defects, while SEM showed the production of polymer particles with commercially desirable uniform, ‘popcorn’, morphology. GPC analysis showed the production of polyethylenes with Mw S B M e 2 (Cp,I*)Zr(CH2SiMe3)2 was immobilised on MAO modified layered double hydroxide (LDHMAO). The slurry-phase polymerisation activity of S B M e 2 (Cp,I*)Zr(CH2SiMe3)2 on this support system was similar to the sMAO support; however, the polymer morphology was much less uniform.
- Published
- 2020
19. Ammonia Activation, H2 Evolution and Nitride Formation from a Molybdenum Complex with a Chemically and Redox Noninnocent Ligand
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Zoë R. Turner, Paul J. Chirik, Máté J. Bezdek, and Grant W. Margulieux
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010405 organic chemistry ,Ligand ,chemistry.chemical_element ,Cooperativity ,General Chemistry ,Nitride ,010402 general chemistry ,Photochemistry ,Hydrogen atom abstraction ,01 natural sciences ,Biochemistry ,Redox ,Catalysis ,0104 chemical sciences ,Ammonia ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,chemistry ,Molybdenum ,Pyridine ,Polymer chemistry - Abstract
Treatment of the bis(imino)pyridine molybdenum η6-benzene complex (iPrPDI)Mo(η6-C6H6) (iPrPDI, 2,6-(2,6-iPr2C6H3N═CMe)2C5H3N) with NH3 resulted in coordination induced haptotropic rearrangement of the arene to form (iPrPDI)Mo(NH3)2(η2-C6H6). Analogous η2-ethylene and η2-cyclohexene complexes were also synthesized, and the latter was crystallographically characterized. All three compounds undergo loss of the η2-coordinated ligand followed by N–H bond activation, bis(imino)pyridine modification, and H2 loss. A dual ammonia activation approach has been discovered whereby reversible M–L cooperativity and coordination induced bond weakening likely contribute to dihydrogen formation. Significantly, the weakened N–H bonds in (iPrPDI)Mo(NH3)2(η2-C2H4) enabled hydrogen atom abstraction and synthesis of a terminal nitride from coordinated ammonia, a key step in NH3 oxidation.
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- 2017
20. Polymethylaluminoxane supported zirconocene catalysts for polymerisation of ethylene
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Thomas Arnold, Jean-Charles Buffet, Zoë R. Turner, and Dermot O'Hare
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Ethylene ,010405 organic chemistry ,Chemistry ,Organic Chemistry ,Nuclear magnetic resonance spectroscopy ,010402 general chemistry ,01 natural sciences ,Biochemistry ,0104 chemical sciences ,Catalysis ,Inorganic Chemistry ,chemistry.chemical_compound ,Polymerization ,Ethylene polymerization ,Phase (matter) ,Polymer chemistry ,Materials Chemistry ,Slurry ,Density functional theory ,Physical and Theoretical Chemistry - Abstract
We report here the synthesis of two new ansa-bridged permethylindenyl zirconocenes, their reaction with solid polymethylaluminoxane (sMAO) and their use in slurry phase ethylene polymerisation. Meso-(EBI*)Zr(CH2Ph)2 and meso-(EBI*)Zr(CH2tBu)Cl, (EBI* = ethylenebis[1-(2,3,4,5,6,7-hexamethylindenyl)]) were synthesised from meso-(EBI*)ZrCl2 and KCH2Ph and LiCH2tBu respectively. The new zirconocenes were characterised by NMR spectroscopy and X-ray crystallography, and density functional theory calculations were carried out. Solid precatalysts were obtained when these compounds were reacted with the polymethylaluminoxane support. Ethylene polymerisation activities of up to 6000 kgPE/molZr/h/bar were obtained in the slurry polymerisation of ethylene. The polyethylenes showed molecular weights, Mw, above 200 000 kg/mol and low polydispersities, Mw/Mn
- Published
- 2016
21. Bismuth Pyridine Dipyrrolide Complexes: a Transient Bi(II) Species Which Ring Opens Cyclic Ethers
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Zoë R. Turner
- Subjects
010405 organic chemistry ,Reducing agent ,Complex formation ,chemistry.chemical_element ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Bismuth ,Inorganic Chemistry ,Solvent ,Metal ,chemistry.chemical_compound ,chemistry ,visual_art ,Cyclic ether ,Polymer chemistry ,Pyridine ,visual_art.visual_art_medium ,Redistribution (chemistry) ,Physical and Theoretical Chemistry - Abstract
A family of group 15 MIII pyridine dipyrrolide complexes has been prepared and fully characterized; the reduction of these complexes was investigated with traditional strong metal reductants, which led either to over-reduction in the case of Mg and Zn or to ligand redistribution and "ate" complex formation when KC8 was used. However, by utilizing organosilanes as soluble reductants, the ring opening and two electron reduction of thf solvent was observed with concomitant formation of Bi-C and Si-O bonds; this is an example of a main group complex that is capable of ring opening a cyclic ether in the absence of additional metal reducing agents. The proposed BiII intermediate in this mechanism could be trapped using the stable organic radical TEMPO.
- Published
- 2019
22. Synthesis, Structure, and Hydrogenolysis of Pyridine Dicarbene Iron Dialkyl Complexes
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Stephan M. Rummelt, Jonathan M. Darmon, Grant W. Margulieux, Shunlin Gu, Zoë R. Turner, Renyuan Pony Yu, Tyler P. Pabst, Paul J. Chirik, and Peter Viereck
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Iron hydride ,Deuterated benzene ,010405 organic chemistry ,Chemistry ,Ligand ,Organic Chemistry ,010402 general chemistry ,01 natural sciences ,Medicinal chemistry ,Article ,0104 chemical sciences ,Catalysis ,Inorganic Chemistry ,Solvent ,chemistry.chemical_compound ,Hydrogenolysis ,Pyridine ,Chelation ,Physical and Theoretical Chemistry - Abstract
Two methods for the synthesis of bis(imidazol-2-ylidene)pyridine iron dialkyl complexes, (CNC)Fe(CH(2)SiMe(3))(2), have been developed. The first route consists of addition of two equivalents of LiCH(2)SiMe(3) to the iron dihalide complex, (CNC)FeBr(2), while the second relies on addition of the free CNC ligand to readily-prepared (py)(2)Fe(CH(2)SiMe(3))(2) (py = pyridine). With aryl-substituted CNC ligands, octahedral complexes of the type ((Ar)CNC)Fe(CH(2)SiMe(3))(2)(N(2)) ((Ar)CNC = bis(arylimidazol-2-ylidene)pyridine) were isolated, where the dinitrogen ligand occupies the site trans to the pyridine of the CNC-chelate. In contrast, the alkyl-substituted variant, ((tBu)ACNC)Fe(CH(2)SiMe(3))(2) ((tBu)ACNC = 2,6-((t)Bu-imidazol-2-ylidene)(2)pyridine) was isolated as the five-coordinate compound lacking dinitrogen. Exposure of the ((Ar)CNC)Fe(CH(2)SiMe(3))(2)(N(2)) derivatives to an H(2) atmosphere resulted in formation of the corresponding iron hydride complexes ((Ar)CNC)FeH(4). These compounds catalyzed hydrogen isotope exchange between the deuterated benzene solvent and H(2), generating isotopologues and isotopomers of ((Ar)CNC)Fe(H(n))(D(4-n)) (n = 0–4). When (3,5-Me(2)(Mes)CNC)Fe(CH(2)SiMe(3))(2)(N(2)) (3,5-Me(2)(Mes)CNC = 2,6-(2,4,6-Me(3)-C6H2-imidazol-2-ylidene)(2)-3,5-Me(2)-pyridine) was treated successively with H(2) and then N(2), the corresponding reduced dinitrogen complex (3,5-Me(2)(Mes)CNC)Fe(N(2))(2) was isolated. The same product was also obtained following addition of pinacolborane to (3,5-Me(2)(Mes)CNC)Fe(CH(2)SiMe(3))(2)(N(2)).
- Published
- 2019
23. Group 4 permethylindenyl complexes for the polymerisation of L-, D- and rac-lactide monomers
- Author
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Joshua E. Matley, Dermot O'Hare, Jean-Charles Buffet, Jessica V. Lamb, Christopher M. R. Wright, and Zoë R. Turner
- Subjects
Lactide ,010405 organic chemistry ,Nuclear magnetic resonance spectroscopy ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Catalysis ,Inorganic Chemistry ,Solvent ,chemistry.chemical_compound ,Monomer ,chemistry ,Polymerization ,Benzyl alcohol ,Tacticity ,Polymer chemistry - Abstract
A series of well-defined group 4 permethylindenyl complexes have been prepared and fully characterised by NMR spectroscopy and X-ray crystallography. Me2SB(Cp,I*)ZrCl2 ({(η5-C9Me6)Me2Si(η5-C5H4)}ZrCl2; 1), Me2SB(CpMe,I*)ZrCl2 ({(η5-C9Me6)Me2Si(η5-C5H3Me)}ZrCl2; 2), Me2SB(Cp,I*)HfCl2 (3) and Z-Me2SB(Cp,I*)ZrCl(O-2,6-Me-C6H3) (4) were investigated as initiators for the ring-opening polymerisation (ROP) of l-, d- and rac-lactide monomers in the presence of benzyl alcohol. 1-4 displayed second order dependence on monomer concentration and produced isotactic and heterotactic (Pr = 0.81) polylactides for the polymerisation of l-, d- and rac-lactide respectively. The effects of temperature, catalyst concentration, co-initiator concentration, solvent and scale were studied. At 80 °C, with two equivalents of benzyl alcohol, 4 was the most active initiator for the ROP of l-, d- and rac-lactide (kobs = 6.39, 6.38 and 5.89 M-1 h-1 respectively). The polylactides were characterised by NMR spectroscopy, GPC and MALDI-TOF mass spectrometry.
- Published
- 2019
24. Group 4 permethylindenyl complexes for slurry-phase polymerisation of ethylene
- Author
-
Jean-Charles Buffet, Dermot O'Hare, Zoë R. Turner, and Jessica V. Lamb
- Subjects
Ethylene ,Morphology (linguistics) ,Polymers and Plastics ,Organic Chemistry ,Bioengineering ,02 engineering and technology ,Polyethylene ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Biochemistry ,0104 chemical sciences ,Catalysis ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,Polymerization ,Phase (matter) ,Slurry ,Hydroxide ,0210 nano-technology - Abstract
A series of ten well-defined group 4 ansa-bridged permethylindenyl complexes have been prepared, fully characterised and supported on inorganic solid supports. These catalysts were investigated in the slurry-phase polymerisation of ethylene. A range of inorganic solid supports have been utilised; solid polymethylaluminoxane (sMAO), MAO modified layered double hydroxide (LDHMAO) and MAO modified silica (SSMAO). The sMAO supported catalytic systems exhibit some of the highest slurry-phase polymerisation activities reported in literature with activities reaching 9509 kg PE mol M-1 h -1 bar -1 for Me2 SB(Cp Me ,I∗)ZrMe 2 at 80 °C after 5 minutes of polymerisation; 34% more active than an industrial standard under similar conditions. These systems produce polyethylenes with low molecular weights, M w , reaching as low as 46 kg mol -1 for E- Me2 SB(Cp nBu ,I∗)ZrCl 2 at 90 °C after 30 minutes of polymerisation with a uniform, mono-disperse "popcorn" morphology. The sMAO supported systems show much higher catalytic activities and much more industrially desirable polyethylene morphology than the same complexes supported on LDHMAO and SSMAO.
- Published
- 2019
25. Magnesium, calcium and zinc [N
- Author
-
Mariana, Luna Barros, Michael G, Cushion, Andrew D, Schwarz, Zoë R, Turner, and Philip, Mountford
- Abstract
A new family of sterically demanding N2N' heteroscorpionate pro-ligands (HC(tBu2pz)2SiMe2N(H)R (R = iPr, tBu, Ph, Xyl)) has been prepared via a straightforward modular synthetic route. An extensive study into the synthesis and characterisation of lithium, magnesium, calcium and zinc complexes supported by both 3,5-tBu and 3,5-Me substituted N2N' ligand families has been conducted. Attempted deprotonation of the pro-ligands with nBuLi afforded the corresponding lithium salts Li{HC(tBu2pz)2SiMe2NR} (R = iPr (1), tBu (2), Ph (3) and Xyl (4)) but air- and thermal-sensitivity limited the yields of these potentially useful precursors; only the sterically encumbered ligand system allowed clean reactivity. Magnesium methyl complexes Mg{HC(tBu2pz)2SiMe2NR}Me (R = iPr (5) and R = Ph (6)) were prepared using an excess of the Grignard reagent MeMgCl. Magnesium butyl complexes were synthesised in good yields using the dialkyl precursor MgnBu2 to afford Mg{HC(R'2pz)2SiMe2NR}nBu (R' = Me; R = iPr (7), tBu (8), Ad (9), Ph (10). R' = tBu; R = iPr (11), Ph (12)). Protonolylsis reactions were used to synthesise magnesium and calcium amide complexes Mg{HC(R'2pz)2SiMe2NR}{N(SiHMe2)2} (R' = Me; R = iPr (13), tBu (14), Ph (15). R' = tBu; R = Ph (16)) or Mg{HC(R'2pz)2SiMe2NR}{N(SiMe3)2} (R' = Me; R = iPr (17), tBu (18), Ph (19). R' = tBu; R = Ph (20)), and Ca{HC(R'2pz)2SiMe2NR}{N(SiMe2)2} (L) (R' = Me; L = thf; R = iPr (21), tBu (22), Ph (23). R' = tBu; L = none; R = Ph (24). Zinc methyl complexes Zn{HC(R'2pz)2SiMe2NR}Me (R' = Me; R = iPr (25), tBu (26), Ph (27). R' = tBu; R = Ph (28)) were prepared by reaction of the N2N' heteroscorpionate pro-ligands with ZnMe2. In preliminary studies, magnesium amide complexes 16 and 20 were evaluated as initiators for the ring-opening polymerisation (ROP) of ε-caprolactone (ε-CL) and rac-lactide (rac-LA). Although the overall polymerisation control was poor, 16 and 20 were found to be active initiators.
- Published
- 2019
26. Synthesis, characterisation and ethylene polymerisation performance of silyl bridged peralkylated bis(indenyl) zirconocenes
- Author
-
Jean-Charles Buffet, Phakpoom Angpanitcharoen, Dermot O'Hare, Jessica V. Lamb, and Zoë R. Turner
- Subjects
Silylation ,010405 organic chemistry ,Process Chemistry and Technology ,Comonomer ,Methylaluminoxane ,010402 general chemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Polymerization ,Ethylene polymerization ,Polymer chemistry ,Hydroxide ,High-density polyethylene ,Physical and Theoretical Chemistry - Abstract
Six new peralkylated bis(indenyl) zirconocene complexes have been synthesised and fully characterised; rac-Me2SB(3-EtI*)ZrX2 and meso-Me2SB(3-EtI*)ZrX2 (X = Cl, Br and CH2Ph). Solution-phase ethylene polymerisation using rac-Me2SB(3-EtI*)ZrCl2/methylaluminoxane (MAO) and slurry-phase ethylene polymerisation using rac-Me2SB(3-EtI*)ZrCl2 immobilised on solid polymethylaluminoxane (sMAO), MAO modified layered double hydroxide (LDHMAO) and MAO modified silica (SSMAO) were studied. Polymerisation conditions were optimised for sMAO-rac-Me2SB(3-EtI*)ZrCl2 and applied to the other catalysts. A 75:25 mixture of rac- and meso-Me2SB(3-EtI*)Zr(CH2Ph)2 supported on sMAO showed the highest polymerisation activities (4832 kgPEmolZr−1 h−1 bar−1 at 60 °C), producing high density polyethylenes (HDPE) with modest molecular weights (Mw of 336 kg mol−1 at 60 °C) and molecular weight distributions (Mw/Mn) less than 3.2. sMAO-rac-Me2SB(3-EtI*)ZrCl2 was found to be responsive to H2 in a high-throughput screening system, producing polyethylenes with low molecular weights (Mw of 41 kg mol−1 with 1.6% H2). In the same high-throughput system, slurry-phase ethylene polymerisation in the presence of 1-hexene comonomer was shown to increase the polymerisation activity of sMAO-rac-Me2SB(3-EtI*)ZrCl2) compared to polymerisation in the same system without 1-hexene.
- Published
- 2020
27. Supported bis(peralkylindenyl)metallocene catalysts for slurry phase ethylene polymerisation
- Author
-
George A. Hay, Phakpoom Angpanitcharoen, Zoë R. Turner, Dermot O'Hare, Jean-Charles Buffet, and Thomas Arnold
- Subjects
Zirconium ,010405 organic chemistry ,Chemistry ,chemistry.chemical_element ,Nuclear magnetic resonance spectroscopy ,010402 general chemistry ,Mass spectrometry ,01 natural sciences ,0104 chemical sciences ,Catalysis ,Inorganic Chemistry ,chemistry.chemical_compound ,Polymerization ,Phase (matter) ,Polymer chemistry ,Materials Chemistry ,Slurry ,Physical and Theoretical Chemistry ,Metallocene - Abstract
A series of bis(peralkylindenyl)zirconocene and hafnocene complexes were synthesised and characterised by NMR spectroscopy, mass spectrometry and elemental analyses. 3-ethyl-2,4,5,6,7-pentamethylindanone, ( 3-Et Ind # [Formula presented] 3-ethyl-2,4,5,6,7-pentamethylindene, ( 3-Et Ind # )H, and rac-3-ethyl-2,4,5,6,7-pentamethylindenylhafnium dichloride, rac-( 3-Et Ind # ) 2 HfCl 2 , were also characterised by X-ray crystallography. rac- and meso-( 3-Et Ind # ) 2 MCl 2 (M = Zr or Hf) were obtained from the reaction of ( 3-Et Ind # )Li with ZrCl 4 or HfCl 4 . The group 4 metallocenes were then reacted with methylaluminoxane-functionalised silica (SSMAO) to afford silica supported catalysts. A mixture of rac- and meso-( 3-Et Ind # ) 2 ZrCl 2 supported on SSMAO demonstrated an initial polymerisation activity of 250 kg PE /mol M /h/bar. At 70 °C, using rac-( 3-Et Ind # ) 2 ZrCl 2 , solution phase polymerisation activities were twenty times faster than slurry phase polymerisation using SSMAO-rac-( 3-Et Ind # ) 2 ZrCl 2 (1243 and 75 kg PE /mol Zr /h/bar respectively).
- Published
- 2016
28. Titanium and Zirconium Permethylpentalene Complexes, Pn*MCpRX, as Ethylene Polymerization Catalysts
- Author
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Dermot O'Hare, Duncan A. X. Fraser, Zoë R. Turner, and Jean-Charles Buffet
- Subjects
Zirconium ,010405 organic chemistry ,Chemistry ,Ligand ,Organic Chemistry ,Inorganic chemistry ,chemistry.chemical_element ,Nuclear magnetic resonance spectroscopy ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Catalysis ,Inorganic Chemistry ,chemistry.chemical_compound ,Phase (matter) ,Hydroxide ,Physical and Theoretical Chemistry ,Nuclear chemistry ,Bar (unit) ,Titanium - Abstract
A family of group 4 permethylpentalene complexes, Pn∗MCpRX (M = Ti, Zr; CpR = Cp, CpMe, CptBu, CpnBu, CpMe3, Ind; X = Cl, Me), has been synthesized and fully characterized by multinuclear NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction studies. These complexes were immobilized on an insoluble polymethylaluminoxane (sMAO), MAO-modified silica (ssMAO), and a MAO-modified layered double hydroxide (LDH-MAO). The effect of substitution around the Cp ligand was examined in relation to their performance (activity, Mw, PDI, polymer morphology) for ethylene polymerization measured both in solution and in slurry phase. Maximum solution-phase activities of 3585 kg/mol·h·bar were recorded at modest [Zr]:[Al] ratios of 1:250. These were compared to the activities recorded using the equivalent solid-supported complexes, and it was observed that sMAO was a superior support material with average increases in activity of 5.3 and 2.3 times relative to ssMAO and LDH-MAO, respectively. Most striking was the observation that slurry-phase ethylene polymerization activities using equivalent precatalysts supported on sMAO showed enhanced performance compared to the solution phase up to a maximum of 4486 kg/mol·h·bar.
- Published
- 2016
29. Synthesis of Iron Hydride Complexes Relevant to Hydrogen Isotope Exchange in Pharmaceuticals
- Author
-
Paul J. Chirik, Renyuan Pony Yu, Jonathan M. Darmon, Scott P. Semproni, and Zoë R. Turner
- Subjects
Iron hydride ,010405 organic chemistry ,Chemistry ,Hydride ,Organic Chemistry ,Inorganic chemistry ,Partial pressure ,010402 general chemistry ,01 natural sciences ,Oxidative addition ,0104 chemical sciences ,Catalysis ,Inorganic Chemistry ,Solvent ,chemistry.chemical_compound ,Deuterium ,Pyridine ,Physical and Theoretical Chemistry - Abstract
Addition of H2 gas to the bis(arylimidazolin-2-ylidene)pyridine iron bis(dinitrogen) complex (H4-iPrCNC)Fe(N2)2 resulted in facile oxidative addition of the H–H bond to yield a mixture of (H4-iPrCNC)FeH4 and trans-(H4-iPrCNC)FeH2(N2), depending on the partial pressures of H2 and N2. Both iron hydride complexes were characterized by X-ray diffraction and proved relevant to the catalytic hydrogen isotope exchange of arene C(sp2)–H bonds. Activation of the benzene-d6 solvent at ambient temperature produced deuterated isotologues of both compounds that exhibit large isotopic perturbation of resonances in the hydride signals.
- Published
- 2017
30. Synthesis and characterization of permethylpentalene titanium aryloxide and alkoxide complexes
- Author
-
Daniel D. Clement, F. Mark Chadwick, Zoë R. Turner, Samantha C. Binding, Jean-Charles Buffet, Ian J. Casely, Thomas Arnold, and Dermot O'Hare
- Subjects
chemistry.chemical_classification ,010405 organic chemistry ,Ligand ,Salt (chemistry) ,chemistry.chemical_element ,Nuclear magnetic resonance spectroscopy ,Planar chirality ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Stereocenter ,Inorganic Chemistry ,chemistry.chemical_compound ,Crystallography ,chemistry ,Alkoxide ,Materials Chemistry ,Physical and Theoretical Chemistry ,Single crystal ,Titanium - Abstract
A series of titanium complexes containing the permethylpentalene ligand (C8Me62−; Pn∗) – Pn∗Ti(O-2,6-Me-C6H3)Cl (1), Pn∗Ti(O-2,4-tBu-C6H3)Cl (2), Pn∗Ti(OtBu)Cl (3), Pn∗Ti(O-2,6-Me-C6H3)2 (4), Pn∗Ti(OtBu)2 (5) – or the (hydro)permethylpentalene ligand (C8Me6H−; Pn∗(H)) – Pn∗(H)Ti(O-2,6-Me-C6H3)Cl2 (6) and Pn∗(H)Ti(O-2,6-Me2-C6H3)3 (7) – were prepared by the reaction of [Pn∗TiCl(μ-Cl)]2 with the corresponding potassium salt or alcohol. All complexes have been characterized by single crystal X-ray diffraction studies and NMR spectroscopy. The (hydro)permethylpentalene complexes contain a stereocenter and planar chirality which can be described as R,RP or S,SP configurations.
- Published
- 2018
31. Popcorn-shaped polyethylene synthesised using highly active supported permethylindenyl metallocene catalyst systems
- Author
-
Jean-Charles Buffet, Zoë R. Turner, and Dermot O'Hare
- Subjects
chemistry.chemical_classification ,Materials science ,Ethylene ,010405 organic chemistry ,Metals and Alloys ,Bent metallocene ,General Chemistry ,Polymer ,Post-metallocene catalyst ,Polyethylene ,010402 general chemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,chemistry ,Polymerization ,Phase (matter) ,Polymer chemistry ,Materials Chemistry ,Ceramics and Composites - Abstract
Unsymmetrical permethylindenyl bent metallocene complexes have been synthesised and reacted with inorganic solid supports to afford catalysts for the slurry phase polymerisation of ethylene. Those supported on solid polymethylaluminoxane were both highly active catalysts and afforded polymers with a desirable, low aggregation, "popcorn" morphology.
- Published
- 2018
32. Synthesis, characterisation, and polymerisation studies of hexamethylindenyl zirconocenes and hafnocenes
- Author
-
Jean-Charles Buffet, Zoë R. Turner, Dermot O'Hare, and Thomas Arnold
- Subjects
Zirconium ,Chemistry ,Ligand ,Organic Chemistry ,chemistry.chemical_element ,Nuclear magnetic resonance spectroscopy ,Biochemistry ,Medicinal chemistry ,Catalysis ,Inorganic Chemistry ,chemistry.chemical_compound ,Polymerization ,Materials Chemistry ,Organic chemistry ,Density functional theory ,Physical and Theoretical Chemistry ,Single crystal ,Metallocene - Abstract
A family of group 4 metallocene complexes based on the hexamethylindenyl ligand (C9Me6H; Ind#) have been prepared and fully characterised. The complexes rac- Ind 2 # ZrCl2 (rac-1), meso- Ind 2 # ZrCl2 (meso-1), rac- Ind 2 # HfCl2 (rac-2), meso- Ind 2 # HfCl2 (meso-2) were prepared by the reaction of Ind#Li with the corresponding MCl4 (where M = Zr, Hf); and rac- Ind 2 # Zr(CH2Ph)2 (rac-3) was derived from rac-1 using two equivalents of potassium benzyl (KCH2Ph). All five species were characterised by NMR spectroscopy, single crystal X-ray diffraction and studied using density functional theory. The zirconocenes were tested for their activity as solution-phase ethylene polymerisation catalysts and rac-1 was found to outperform the meso-1 at most temperatures. The benzyl analogue, rac-3, peaked at more than double the activity reported for the dihalide species.
- Published
- 2015
33. Ethylene polymerisation using solid catalysts based on layered double hydroxides
- Author
-
Jean-Charles Buffet, Dermot O'Hare, Robert Cooper, and Zoë R. Turner
- Subjects
Ethylene ,Aqueous solution ,Polymers and Plastics ,Catalyst support ,Organic Chemistry ,Layered double hydroxides ,Methylaluminoxane ,Bioengineering ,engineering.material ,Polyethylene ,Biochemistry ,Catalysis ,chemistry.chemical_compound ,chemistry ,Polymer chemistry ,engineering ,Hydroxide - Abstract
We report here the use of methylaluminoxane (MAO) modified aqueous miscible organic solvent treated (AMOST) layered double hydroxide, Mg6Al2(OH)16CO3·4H2O (AMO-Mg3Al-CO3) as a catalyst support system for the slurry phase polymerisation of ethylene using immobilised metallocene and non-metallocene metal complexes. The polymerisation data demonstrates that the catalyst productivity is dependent on the thermal treatment of the LDH and the temperature, pressure and time of the polymerisation. The solid catalyst system, AMO-Mg3Al-CO3/MAO/(MesPDI)FeCl2 has been shown to have the highest overall activity for a non-metallocene system (14166 kgPE mol−1complex h−1 bar−1), and AMO-Mg3Al-CO3/MAO/(2-Me,4-PhSBI)ZrCl2 was the most productive for a metallocene-based system (∼3300 kgPE mol−1complex h−1 bar−1). The molecular weights and polydispersities vary with the complex on the AMO-LDH surface. Scanning electron microscopy images show that the morphology of the as produced polyethylene mimics that of the LDH support.
- Published
- 2015
34. Synthesis and characterisation of permethylindenyl zirconium complexes and their use in ethylene polymerisation
- Author
-
Jean-Charles Buffet, Thomas Arnold, Zoë R. Turner, Dermot O'Hare, and Phakpoom Angpanitcharoen
- Subjects
Zirconium ,Ethylene ,General Chemical Engineering ,Inorganic chemistry ,Layered double hydroxides ,chemistry.chemical_element ,General Chemistry ,Nuclear magnetic resonance spectroscopy ,engineering.material ,Catalysis ,chemistry.chemical_compound ,chemistry ,Polymerization ,Ethylene polymerization ,Polymer chemistry ,engineering ,Density functional theory - Abstract
We report the synthesis of two zirconocenes, dimethylsilylbis(hexamethylindenyl) zirconium dichloride, rac-(SBI*)ZrCl2, and nbutyldimethylsilyl(hexamethylindenyl) zirconium trichloride, [(Ind*SiMe2nBu)Zr(μ-Cl)Cl2]2. The complexes were characterised by NMR spectroscopy and X-ray crystallography, and the bonding was evaluated using density functional theory. rac-(SBI*)ZrCl2 demonstrated a very high activity for solution phase polymerisation of ethylene (ca. 22 500 kgPE−1 molZr−1 h−1 bar−1). Both rac-(SBI*)ZrCl2 and rac-(EBI*)ZrCl2 (EBI* = ethylenebis(hexamethylindenyl)) have been supported on MAO modified silica and AMOST layered double hydroxides (AMO-LDHs), and evaluated as catalysts in the slurry-phase polymerisation of ethylene. The highest catalytic polymerisation activities for rac-(SBI*)ZrCl2 and rac-(EBI*)ZrCl2 on the layered double hydroxides were 9657 and 4325 kgPE−1 molZr−1 h−1 bar−1 respectively, for MAO modified Mg2Al–SO4 LDH. However, rac-(EBI*)ZrCl2 was a three times more active catalyst than rac-(SBI*)ZrCl2 when supported on silica.
- Published
- 2015
35. Selective ethylene oligomerisation using supported tungsten mono-imido catalysts
- Author
-
Jean-Charles Buffet, Thomas J. Williams, Christopher M. R. Wright, Dermot O'Hare, and Zoë R. Turner
- Subjects
Steric effects ,Ethylene ,010405 organic chemistry ,Stereochemistry ,Solid-state ,chemistry.chemical_element ,Tungsten ,010402 general chemistry ,01 natural sciences ,Medicinal chemistry ,Chloride ,0104 chemical sciences ,Catalysis ,Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,medicine ,Trimethylaluminium ,Selectivity ,medicine.drug - Abstract
A series of substituted phenyl mono-imido complexes of the type W(NR)Cl4(THF) (R = C6H5, 2,6-Me-C6H3, 3,5-Me-C6H3, 2,4,6-Me-C6H2, 4-OMe-C6H4, 2,6-F-C6H3 and 3,5-CF3-C6H3) have been synthesised and characterised. Reaction of these complexes with solid polymethylaluminoxane (sMAO) leads to immobilisation and in situ methylation of the chloride positions on the surface of the support. Reaction of W(NR)Cl4(THF) with trimethylaluminium (TMA) yields the trimethyl complexes W(NR)Me3Cl. Immobilisation of the isotopically labelled W{N(2,6-F-C6H3)}(13CH3)3Cl on sMAO furnished the supported complex with two identifiable methyl resonances in the 13C–{1H} solid state CPMAS spectrum (45 and 56 ppm), with the latter matching the unsupported complex, confirming retention of the structure on the surface. The sMAO-supported complexes (W : Al = 1 : 150) were tested for their propensity to dimerise ethylene (1 bar) in d6-benzene at 100 °C and compared with the previously reported sMAO-W{N(2,6-iPr-C6H3)}Cl4(THF) (sMAO-1.a). Complexes with electron deficient imido groups were shown to be the most active, and increased steric bulk in the ortho positions is also an important factor, with sMAO acting as a support, scavenger and activator. sMAO-W{N(3,5-CF3-C6H3)}Cl4(THF) was the most active, demonstrating a turnover frequency of 5.65 molC2H4 mol−1W h−1 and a selectivity towards 1-butene of 91% after 8 h.
- Published
- 2017
36. Ammonia Activation, H
- Author
-
Grant W, Margulieux, Máté J, Bezdek, Zoë R, Turner, and Paul J, Chirik
- Abstract
Treatment of the bis(imino)pyridine molybdenum η
- Published
- 2017
37. Electronic Structure Determination of Pyridine N-Heterocyclic Carbene Iron Dinitrogen Complexes and Neutral Ligand Derivatives
- Author
-
Serena DeBeer, Renyuan Pony Yu, Jonathan M. Darmon, Paul J. Chirik, Zoë R. Turner, Scott P. Semproni, and S. Chantal E. Stieber
- Subjects
Absorption spectroscopy ,Ligand ,Radical ,Organic Chemistry ,Inorganic chemistry ,Electronic structure ,Acceptor ,Article ,Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,Pyridine ,Polymer chemistry ,Mössbauer spectroscopy ,Physical and Theoretical Chemistry ,Carbene - Abstract
The electronic structures of pyridine N-heterocyclic dicarbene (iPrCNC) iron complexes have been studied by a combination of spectroscopic and computational methods. The goal of these studies was to determine if this chelate engages in radical chemistry in reduced base metal compounds. The iron dinitrogen example (iPrCNC)Fe(N2)2 and the related pyridine derivative (iPrCNC)Fe(DMAP)(N2) were studied by NMR, Mössbauer, and X-ray absorption spectroscopy and are best described as redox non-innocent compounds with the iPrCNC chelate functioning as a classical π acceptor and the iron being viewed as a hybrid between low-spin Fe(0) and Fe(II) oxidation states. This electronic description has been supported by spectroscopic data and DFT calculations. Addition of N,N-diallyl-tert-butylamine to (iPrCNC)Fe(N2)2 yielded the corresponding iron diene complex. Elucidation of the electronic structure again revealed the CNC chelate acting as a π acceptor with no evidence for ligand-centered radicals. This ground state is in contrast with the case for the analogous bis(imino)pyridine iron complexes and may account for the lack of catalytic [2π + 2π] cycloaddition reactivity.
- Published
- 2014
38. Chiral Group 4 Cyclopentadienyl Complexes and Their Use in Polymerization of Lactide Monomers
- Author
-
Jean-Charles Buffet, Zoë R. Turner, and Dermot O'Hare
- Subjects
Lactide ,Ligand ,Stereochemistry ,Organic Chemistry ,Diastereomer ,Medicinal chemistry ,Inorganic Chemistry ,chemistry.chemical_compound ,Monomer ,Enantiopure drug ,chemistry ,Cyclopentadienyl complex ,Alkoxide ,Physical and Theoretical Chemistry ,Methyl group - Abstract
A family of group 4 alkoxide and aryloxide complexes of a chiral cyclopentadienyl-derived (hydro)permethylpentalenyl ligand (C8Me 6H; Pn*(H)) have been prepared and fully characterized. Both racemic and enantiopure complexes of all group 4 congeners were prepared with a wide variety of alkoxide and aryloxide ligands. The complexes Pn*(H)Ti(OtBu)3 (1), Pn*(H)Ti(O-2,6-Me-C 6H3)3 (2), Pn*(H)Zr(OtBu) 3 (3), Pn*(H)Zr(OCH2Ph)3 (4), Pn*(H)Zr(S-OCH{CH3}C6H5)3 (5), Pn*(H)Zr(rac-OCH{CH3}C6H5)3 (6), Pn*(H)Zr(O-2,6-Me-C6H3)3 (7), Pn*(H)Zr(O-2,6-iPr-C6H3)3 (8), Pn*(H)ZrCl2(O-2,6-tBu-C6H3) (9), Pn*(H)Hf(O-2,6-Me-C6H3)3 (10), Pn*(H)HfCl(O-2,6-iPr-C6H3)2, (11), and Pn*(H)HfCl2(O-2,6-tBu-C6H 3) (12) were prepared by the reaction of Pn*(H)MCl3 complexes with the corresponding potassium alkoxides and aryloxides. Single-crystal X-ray diffraction studies implied that, despite multiple diastereomers being possible for each complex, the diastereomers isolated are limited to configurations in which the methyl group at the chiral center is always oriented anti to the metal center in order to minimize steric hindrance (R,RP and S,SP). The complexes were investigated as initiators for the ring-opening polymerization of l- and rac-lactide in order to ascertain if these mixtures of diastereomers could exert any stereocontrol on the resulting polymerization. Kinetic studies were completed to explore the effects of the metal cation, chiral (hydro)permethylpentalenyl ligand, ancillary ligands, initiator concentration and temperature. Both Pn*(H)Zr(S- OCH{CH3}C6H5)3 and Pn*(H)Zr(rac-OCH{CH3}C6H5)3 demonstrated very high rates of propagation for l- and rac-lactide (1.885 < kobs < 3.442 h-1) at 100 °C. The observed propagation rates using Pn*(H)Zr(rac-OCH{CH3}C 6H5)3 are around 70% faster for l-lactide and rac-lactide in comparison to those using Pn*(H)Zr(S-OCH{CH 3}C6H5)3. The polymers were characterized by NMR spectroscopy, GPC, and MALDI-ToF mass spectrometry in order to investigate the tacticities and polydispersities of the polymerizations. © 2014 American Chemical Society.
- Published
- 2014
39. Reversible Carbon–Carbon Bond Formation Induced by Oxidation and Reduction at a Redox-Active Cobalt Complex
- Author
-
Carsten Milsmann, Crisita Carmen Hojilla Atienza, Zoë R. Turner, Paul J. Chirik, and Scott P. Semproni
- Subjects
Models, Molecular ,Nitrogen ,Pyridines ,Imine ,chemistry.chemical_element ,Electrons ,Photochemistry ,Medicinal chemistry ,Redox ,Inorganic Chemistry ,chemistry.chemical_compound ,Coordination Complexes ,Pyridine ,Physical and Theoretical Chemistry ,Bimetallic strip ,chemistry.chemical_classification ,Cobalt ,Halocarbon ,Carbon ,chemistry ,Carbon–carbon bond ,Benzyl group ,Quantum Theory ,Imines ,Oxidation-Reduction - Abstract
The electronic structure of the diamagnetic pyridine imine enamide cobalt dinitrogen complex, ((iPr)PIEA)CoN2 ((iPr)PIEA = 2-(2,6-(i)Pr2-C6H3N═CMe)-6-(2,6-(i)Pr2-C6H3NC═CH2)C5H3N), was determined and is best described as a low-spin cobalt(II) complex antiferromagnetically coupled to an imine radical anion. Addition of potential radical sources such as NO, PhSSPh, or Ph3Cl resulted in C-C coupling at the enamide positions to form bimetallic cobalt compounds. Treatment with the smaller halocarbon, PhCH2Cl, again induced C-C coupling to form a bimetallic bis(imino)pyridine cobalt chloride product but also yielded a monomeric cobalt chloride product where the benzyl group added to the enamide carbon. Similar cooperative metal-ligand addition was observed upon treatment of ((iPr)PIEA)CoN2 with CH2═CHCH2Br, which resulted in allylation of the enamide carbon. Reduction of Coupled-((iPr)PDI)CoCl (Coupled-((iPr)PDI)CoCl = [2-(2,6-(i)Pr2-C6H3N═CMe)-C5H3N-6-(2,6-(i)Pr2-C6H3N═CCH2-)CoCl]2) with NaBEt3H led to quantitative formation of ((iPr)PIEA)CoN2, demonstrating the reversibility of the C-C bond forming reactions. The electronic structures of each of the bimetallic cobalt products were also elucidated by a combination of experimental and computational methods.
- Published
- 2013
40. Zirconocene alkoxides and aryloxides for the polymerization of L- and rac-lactide
- Author
-
Thomas Arnold, Jean-Charles Buffet, John Jj Coward, George R. Harris, Dermot O'Hare, and Zoë R. Turner
- Subjects
Lactide ,010405 organic chemistry ,Stereochemistry ,Chemistry ,Organic Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Medicinal chemistry ,0104 chemical sciences ,Catalysis ,Inorganic Chemistry ,chemistry.chemical_compound ,Cyclopentadienyl complex ,Polymerization ,Materials Chemistry ,Physical and Theoretical Chemistry - Abstract
A family of well-defined cyclopentadienyl and indenyl group 4 complexes has been prepared. The complexes Cp2ZrCl(O-2,6-Me-C6H3) (1), Cp2Zr(O-2,6-Me-C6H3)2 (2), Cp2ZrMe(O-2,6-Me-C6H3) (3), (Ind)2ZrCl(O-2,6-Me-C6H3) (4), (Ind)2ZrMe(O-2,6-Me-C6H3) (5), (Ind)2ZrMe(OtBu) (6), and rac-(EBI)ZrCl(O-2,6-Me-C6H3) (7) were investigated as catalysts for the polymerization of L- and rac-lactide. (Ind)2ZrMe(OtBu) was shown to be the fastest catalyst. At 100 °C, the rates of polymerization (kobs) for L- and rac-lactide were very similar (0.317 and 0.293 h−1 respectively). However, at 80 °C it was found that polymerization of L-LA (kobs = 0.217 h−1) was twice as fast as rac-LA (kobs = 0.120 h−1).
- Published
- 2016
41. Tungsten imido catalysts for selective ethylene dimerisation
- Author
-
Jean-Charles Buffet, Zoë R. Turner, Dermot O'Hare, and Christopher M. R. Wright
- Subjects
Ethylene ,010405 organic chemistry ,Metals and Alloys ,Layered double hydroxides ,Solid-state ,chemistry.chemical_element ,Homogeneous catalysis ,General Chemistry ,engineering.material ,Tungsten ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,chemistry ,Yield (chemistry) ,Polymer chemistry ,Materials Chemistry ,Ceramics and Composites ,engineering - Abstract
A tungsten imido complex W(NDipp)Me3Cl (Dipp = 2,6-(i)Pr-C6H3) is active for the selective dimerisation of ethylene to yield 1-butene under mild conditions. Immobilisation and activation of W(NDipp)Cl4(THF) on layered double hydroxides, silica or polymethylaluminoxane yields active solid state catalysts for the selective dimerisation of ethylene. The polymethylaluminoxane-based catalyst displays a turnover frequency (4.0 molC2H4 molW(-1) h(-1)) almost 7 times that of the homogeneous catalyst.
- Published
- 2016
42. High-Activity Iron Catalysts for the Hydrogenation of Hindered, Unfunctionalized Alkenes
- Author
-
Jordan M. Hoyt, Grant W. Margulieux, Zoë R. Turner, Paul J. Chirik, Renyuan Pony Yu, and Jonathan M. Darmon
- Subjects
Olefin fiber ,Chemistry ,Noyori asymmetric hydrogenation ,Substrate (chemistry) ,General Chemistry ,Article ,Catalysis ,chemistry.chemical_compound ,Pyridine ,Polymer chemistry ,Organic chemistry ,High activity ,heterocyclic compounds ,Chelation ,High turnover - Abstract
The activity of aryl-substituted bis(imino)pyridine and bis(arylimidazol-2-ylidene)pyridine iron dinitrogen complexes has been evaluated in a series of catalytic olefin hydrogenation reactions. In general, more electron donating chelates with smaller 2,6-aryl substituents produce more active iron hydrogenation catalysts. Establishment of this structure-activity relationship has produced base metal catalysts that exhibit high turnover frequencies for the hydrogenation of unfunctionalized, tri- and tetrasubstituted alkenes, one of the most challenging substrate classes for homogenous hydrogenation catalysts.
- Published
- 2012
43. Azo NN Bond Cleavage with a Redox-Active Vanadium Compound Involving Metal-Ligand Cooperativity
- Author
-
Zoë R. Turner, Paul J. Chirik, Scott P. Semproni, and Carsten Milsmann
- Subjects
Models, Molecular ,Vanadium Compounds ,Pyridines ,Vanadium ,chemistry.chemical_element ,Cooperativity ,Sulfides ,Ligands ,Photochemistry ,Catalysis ,Redox Activity ,Metal ,chemistry.chemical_compound ,Polymer chemistry ,Redox active ,Imide ,Bond cleavage ,Ligand ,Chemistry ,Oxides ,General Medicine ,General Chemistry ,visual_art ,visual_art.visual_art_medium ,Azo Compounds ,Oxidation-Reduction - Published
- 2012
44. Electronic Effects in 4-Substituted Bis(imino)pyridines and the Corresponding Reduced Iron Compounds
- Author
-
Zoë R. Turner, Emil B. Lobkovsky, Paul J. Chirik, and Jonathan M. Darmon
- Subjects
chemistry.chemical_classification ,Organic Chemistry ,Inorganic chemistry ,Substituent ,Direct reduced iron ,Electrochemistry ,Sodium amalgam ,Medicinal chemistry ,Coordination complex ,Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,Pyridine ,Electronic effect ,Physical and Theoretical Chemistry ,Carbon monoxide - Abstract
A family of 4-substituted bis(imino)pyridines, 4-X-iPrPDI (4-X-iPrPDI = 2,6-(2,6-iPr2-C6H3N═CMe)2-4-X-C5H2N; X = CF3, tBu, Bn, NMe2), has been synthesized and the iron coordination chemistry studied. Sodium amalgam reduction of the iron dihalides (4-X-iPrPDI)FeX2 (X = Cl, Br) in the presence of excess carbon monoxide furnished the corresponding iron dicarbonyl compounds (4-X-iPrPDI)Fe(CO)2. Equilibrium mixtures of the four- and five-coordinate iron dinitrogen compounds (4-X-iPrPDI)FeN2 and (4-X-iPrPDI)Fe(N2)2 were prepared by performing the sodium amalgam reduction of the iron dihalides under a dinitrogen atmosphere. Electrochemical and spectroscopic measurements were conducted on the free ligands and the iron derivatives to systematically evaluate the influence of each para pyridine substituent on the electronic structure of the compound.
- Published
- 2012
45. Enantiopure C1-Symmetric Bis(imino)pyridine Cobalt Complexes for Asymmetric Alkene Hydrogenation
- Author
-
Zoë R. Turner, Sebastien Monfette, Scott P. Semproni, and Paul J. Chirik
- Subjects
Models, Molecular ,chemistry.chemical_classification ,Pyridines ,Hydride ,Alkene ,Enantioselective synthesis ,chemistry.chemical_element ,Stereoisomerism ,Cobalt ,General Chemistry ,Alkenes ,Biochemistry ,Medicinal chemistry ,Catalysis ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Enantiopure drug ,chemistry ,Pyridine ,Organic chemistry ,Hydrogenation - Abstract
Enantiopure C(1)-symmetric bis(imino)pyridine cobalt chloride, methyl, hydride, and cyclometalated complexes have been synthesized and characterized. These complexes are active as catalysts for the enantioselective hydrogenation of geminal-disubstituted olefins.
- Published
- 2012
46. Bis(imino)pyridine Iron Dinitrogen Compounds Revisited: Differences in Electronic Structure Between Four- and Five-Coordinate Derivatives
- Author
-
Zoë R. Turner, Jordan M. Hoyt, Carsten Milsmann, Serena DeBeer, Paul J. Chirik, Karl Wieghardt, S. Chantal E. Stieber, and Kenneth D. Finkelstein
- Subjects
Nitrogen ,Pyridines ,Diradical ,Iron ,Imine ,Inorganic chemistry ,Electronic structure ,Medicinal chemistry ,Ferrous ,Inorganic Chemistry ,Spectroscopy, Mossbauer ,chemistry.chemical_compound ,chemistry ,Mössbauer spectroscopy ,Pyridine ,Physical and Theoretical Chemistry ,Ground state ,Isopropyl - Abstract
The electronic structures of the four- and five-coordinate aryl-substituted bis(imino)pyridine iron dinitrogen complexes, ((iPr)PDI)FeN(2) and ((iPr)PDI)Fe(N(2))(2) ((iPr)PDI = 2,6-(2,6-(i)Pr(2)-C(6)H(3)-N=CMe)(2)C(5)H(3)N), have been investigated by a combination of spectroscopic techniques (NMR, Mössbauer, X-ray Absorption, and X-ray Emission) and DFT calculations. Homologation of the imine methyl backbone to ethyl or isopropyl groups resulted in the preparation of the new bis(imino)pyridine iron dinitrogen complexes, ((iPr)RPDI)FeN(2) ((iPr)RPDI = 2,6-(2,6-(i)Pr(2)-C(6)H(3)-N=CR)(2)C(5)H(3)N; R = Et, (i)Pr), that are exclusively four coordinate both in the solid state and in solution. The spectroscopic and computational data establish that the ((iPr)RPDI)FeN(2) compounds are intermediate spin ferrous derivatives (S(Fe) = 1) antiferromagnetically coupled to bis(imino)pyridine triplet diradical dianions (S(PDI) = 1). While this ground state description is identical to that previously reported for ((iPr)PDI)Fe(DMAP) (DMAP = 4-N,N-dimethylaminopyridine) and other four-coordinate iron compounds with principally σ-donating ligands, the d-orbital energetics determine the degree of coupling of the metal-chelate magnetic orbitals resulting in different NMR spectroscopic behavior. For ((iPr)RPDI)Fe(DMAP) and related compounds, this coupling is strong and results in temperature independent paramagnetism where a triplet excited state mixes with the singlet ground state via spin orbit coupling. In the ((iPr)RPDI)FeN(2) family, one of the iron singly occupied molecular orbitals (SOMOs) is essentially d(z(2)) in character resulting in poor overlap with the magnetic orbitals of the chelate, leading to thermal population of the triplet state and hence temperature dependent NMR behavior. The electronic structures of ((iPr)RPDI)FeN(2) and ((iPr)PDI)Fe(DMAP) differ from ((iPr)PDI)Fe(N(2))(2), a highly covalent molecule with a redox noninnocent chelate that is best described as a resonance hybrid between iron(0) and iron(II) canonical forms as originally proposed in 2004.
- Published
- 2012
47. Synthesis and Electronic Structure Determination of N-Alkyl-Substituted Bis(imino)pyridine Iron Imides Exhibiting Spin Crossover Behavior
- Author
-
Serena DeBeer, Emil B. Lobkovsky, Eckhard Bill, Carsten Milsmann, Zoë R. Turner, Karl Wieghardt, Paul J. Chirik, and Amanda C. Bowman
- Subjects
Models, Molecular ,Pyridines ,Spin transition ,Electrons ,Crystallography, X-Ray ,Imides ,Photochemistry ,Ferric Compounds ,Biochemistry ,Catalysis ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Spin crossover ,Pyridine ,Ferrous Compounds ,Imide ,Alkyl ,chemistry.chemical_classification ,Molecular Structure ,Stereoisomerism ,General Chemistry ,Bond length ,Crystallography ,chemistry ,Covalent bond ,Azide - Abstract
Three new N-alkyl substituted bis(imino)pyridine iron imide complexes, ((iPr)PDI)FeNR ((iPr)PDI = 2,6-(2,6-(i)Pr(2)-C(6)H(3)-N═CMe)(2)C(5)H(3)N; R = 1-adamantyl ((1)Ad), cyclooctyl ((Cy)Oct), and 2-adamantyl ((2)Ad)) were synthesized by addition of the appropriate alkyl azide to the iron bis(dinitrogen) complex, ((iPr)PDI)Fe(N(2))(2). SQUID magnetic measurements on the isomeric iron imides, ((iPr)PDI)FeN(1)Ad and ((iPr)PDI)FeN(2)Ad, established spin crossover behavior with the latter example having a more complete spin transition in the experimentally accessible temperature range. X-ray diffraction on all three alkyl-substituted bis(imino)pyridine iron imides established essentially planar compounds with relatively short Fe-N(imide) bond lengths and two-electron reduction of the redox-active bis(imino)pyridine chelate. Zero- and applied-field Mössbauer spectroscopic measurements indicate diamagnetic ground states at cryogenic temperatures and established low isomer shifts consistent with highly covalent molecules. For ((iPr)PDI)FeN(2)Ad, Mössbauer spectroscopy also supports spin crossover behavior and allowed extraction of thermodynamic parameters for the S = 0 to S = 1 transition. X-ray absorption spectroscopy and computational studies were also performed to explore the electronic structure of the bis(imino)pyridine alkyl-substituted imides. An electronic structure description with a low spin ferric center (S = 1/2) antiferromagnetically coupled to an imidyl radical (S(imide) = 1/2) and a closed-shell, dianionic bis(imino)pyridine chelate (S(PDI) = 0) is favored for the S = 0 state. An iron-centered spin transition to an intermediate spin ferric ion (S(Fe) = 3/2) accounts for the S = 1 state observed at higher temperatures. Other possibilities based on the computational and experimental data are also evaluated and compared to the electronic structure of the bis(imino)pyridine iron N-aryl imide counterparts.
- Published
- 2011
48. Covalency in CeIV and UIV Halide and N-Heterocyclic Carbene Bonds
- Author
-
Robert P. Tooze, Ronan Bellabarba, Polly L. Arnold, Panagiota Pelekanaki, Zoë R. Turner, and Nikolas Kaltsoyannis
- Subjects
Lanthanide ,Chemistry(all) ,Inorganic chemistry ,OXIDATION-STATE ,chemistry.chemical_element ,Crystal structure ,Medicinal chemistry ,Catalysis ,DENSITY-FUNCTIONAL THEORY ,chemistry.chemical_compound ,Oxidation state ,TETRAPYRROLE LIGANDS ,lanthanides ,CRYSTAL-STRUCTURE ,N-heterocyclic carbenes ,actinides ,Chemistry ,PORPHYRIN LIGANDS ,Organic Chemistry ,Halogenation ,General Chemistry ,computational chemistry ,Bond order ,LANTHANIDE(III)/ACTINIDE(III) DIFFERENTIATION ,ELECTRONIC-STRUCTURE ,Cerium ,SANDWICH COMPLEXES ,covalency ,CERIUM(IV) COMPLEXES ,METAL-COMPLEXES ,Density functional theory ,Carbene - Abstract
Oxidative halogenation with trityl chloride provides convenient access to CeIV and UIV chloroamides [M(N{SiMe3}2)3Cl] and their N-heterocyclic carbene derivatives, [M(L)(N-{SiMe3}2)2Cl] (L= OCMe2CH2(CNCH2CH2NDipp) Dipp=2,6-iPr2C6H3). Computational analysis of the bonding in these and a fluoro analogue, [U(L)(N{SiMe3}2)2F], provides new information on the covalency in this relative rare oxidation state for molecular cerium complexes. Computational studies reveal increased Mayer bond orders in the actinide carbene bond compared with the lanthanide carbene bond, and natural and atoms-in-molecules analyses suggest greater overall ionicity in the cerium complexes than in the uranium analogues.
- Published
- 2010
49. Functionalised Saturated-Backbone Carbene Ligands: Yttrium and Uranyl Alkoxy-Carbene Complexes and Bicyclic Carbene-Alcohol Adducts
- Author
-
Zoë R. Turner, Christopher D. Carmichael, Polly L. Arnold, and Ian J. Casely
- Subjects
Denticity ,Bicyclic molecule ,Organic Chemistry ,Alcohol ,General Chemistry ,Uranyl ,Catalysis ,Adduct ,chemistry.chemical_compound ,chemistry ,Polymer chemistry ,Alkoxide ,Alkoxy group ,Organic chemistry ,Carbene - Abstract
A new and modular route to bidentate ligands that combines an alkoxide with a saturated backbone N-heterocyclic carbene (NHC) is presented. The bi(heterocyclic) compounds are formally the addition product of a saturated NHC and the alcohol group of the N-functionalised arm. Using these compounds, the synthesis and structural characterisation of the first electropositive metal complexes of saturated N-heterocyclic carbenes has been achieved, and examples structurally characterised for the yttrium(III) and the uranyl [UO(2)](2+) cations.
- Published
- 2008
50. Group 1 and 2 cyclic (alkyl)(amino)carbene complexes
- Author
-
Jean-Charles Buffet and Zoë R. Turner
- Subjects
chemistry.chemical_classification ,Stereochemistry ,Polymer ,Inorganic Chemistry ,Metal ,chemistry.chemical_compound ,Monomer ,chemistry ,Polymerization ,Group (periodic table) ,visual_art ,Polymer chemistry ,visual_art.visual_art_medium ,Carbene ,Alkyl - Abstract
The first examples of cyclic (alkyl)(amino)carbene (CAAC) ligands bound to electropositive metal centres (K, Mg, Sr and Ba) have been isolated and characterised. Preliminary studies demonstrate that all complexes are active for polar monomer polymerisation under ambient conditions affording desirable hydroxyl-terminated telechelic polymers.
- Published
- 2015
Catalog
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