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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.

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.

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).

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.

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).

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.

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.

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.

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.

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

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)).

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

The bis(imino)pyridine 2,6-(2,6-iPr2-C6H3N=CPh)2-C5H3N ((iPr)BPDI) molybdenum dinitrogen complex, [{((iPr)BPDI)Mo(N2)}2(μ2,η(1),η(1)-N2)] has been prepared and contains both weakly (terminal) and modestly (bridging) activated N2 ligands. Addition of ammonia resulted in sequential N-H bond activations, thus forming bridging parent imido (μ-NH) ligands with concomitant reduction of one of the imines of the supporting chelate. Using primary and secondary amines, model intermediates have been isolated that highlight the role of metal-ligand cooperativity in NH3 oxidation.

Two functional groups can be delivered at once to organo-rare earth complexes, (L)MR(2) and (L)(2)MR (M = Sc, Y; L = ({1-C(NDippCH(2)CH(2)N)}CH(2)CMe(2)O), Dipp = 2,6-(i)Pr(2)-C(6)H(3); R = CH(2)SiMe(3), CH(2)CMe(3)), via the addition of E-X across the metal-carbene bond to form a zwitterionic imidazolinium-metal complex, (L(E))MR(2)X, where L(E) = {1-EC(NDippCH(2)CH(2)N)}CH(2)CMe(2)O, E is a p-block functional group such as SiR(3), PR(2), or SnR(3), and X is a halide. The "ate" complex (L(Li))ScR(3) is readily accessible and is best described as a Li carbene adduct, ({1-Li(THF)C(NDippCH(2)CH(2)N)}CH(2)CMe(2)O)Sc(CH(2)SiMe(3))(3), since structural characterization shows the alkoxide ligand bridging the two metals and the carbene Li-bound with the shortest yet recorded Li-C bond distance. This can be converted via lithium halide-eliminating salt metathesis reactions to alkylated or silylated imidazolinium derivatives, (L(E))ScR(3) (E = SiMe(3) or CPh(3)). All the E-functionalized imidazolinium complexes spontaneously eliminate functionalized hydrocarbyl compounds upon warming to room temperature or slightly above, forming new organic products ER, i.e., forming C-Si, C-P, and C-Sn bonds, and re-forming the inorganic metal carbene (L)MR(X) or (L)(2)MX complex, respectively. Warming the tris(alkyl) complexes (L(E))MR(3) forms organic products arising from C-C or C-Si bond formation, which appears to proceed via the same elimination route. Treatment of (L)(2)Sc(CH(2)SiMe(3)) with iodopentafluorobenzene results in the "reverse sense" addition, which upon thermolysis forms the metal aryl complex (L)(2)Sc(C(6)F(5)) and releases the iodoalkane Me(3)SiCH(2)I, again facilitated by the reversible functionalization of the N-heterocyclic carbene group in these tethered systems.

The synthesis of magnesium and zinc complexes of bidentate anionic alkoxide ligands with saturated-backbone carbene groups is reported. Mono(ligand) and bis(ligand) complexes [M(L(R))N''](2) and [M(L(R))(2)] (M = Mg, Zn, N'' = N(SiMe(3))(2), L(R) = [OCMe(2)CH(2){CNCH(2)CH(2)NR}] R = (i)Pr, Mes, Dipp) have been isolated, and some structurally characterised and compared with the new unsaturated carbene complex [Mg(L)(2)]. Reactions with silyl halides show either addition across the metal carbene bond, or across the metal alkoxide bond, in accordance with the metals' electronegativity difference: the metal alkoxide bonds are stronger for Mg(II) complexes, for which the carbene is silylated to form zwitterionic [MgI(Me(3)SiL(R))N''] (Me(3)SiL(R) = OCMe(2)CH(2){Me(3)SiCNCH(2)CH(2)NR}) while the metal-bound alkoxide group is silylated in the Zn(II) complexes forming [ZnI(Me(3)SiOL(R))N''] (Me(3)SiOL(R) = Me(3)SiOCMe(2)CH(2){CNCH(2)CH(2)NR}). The proligand [HL(R)] is silylated at the alcohol group, forming the iodide salt [Me(3)SiOCMe(2)CH(2){HCNCH(2)CH(2)NR}]I.Preliminary results on the use of these complexes as initiators for the polymerisation of rac-lactide are reported, and suggest different initiation mechanisms are occurring for the two metals, in agreement with the different silylation reactivity observed. The polymerisation reactions are facile at room temperature even without an initiator, and yield polymers of reasonable molecular weight and heterotacticity and with good PDI. These are the first magnesium NHC complexes demonstrated to effect lactide polymerisation.Also, an adduct instead of the anticipated potassium alkoxycarbene is generated from the reaction of the proligand [HL(R)] with potassium amide KN''; this has been structurally characterised.

Silyl, phosphinyl, stannyl, and boryl reagents can be added across the neutral metal-carbon dative bond in d0 f-block metal N-heterocyclic carbene complexes in a reversible manner, allowing additional functional groups to be incorporated into redox-inactive organo-f-block compounds.