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This article explores the use of nickel thiocyanate complexes as catalysts for cross-coupling reactions in organic synthesis. The authors investigate the synthesis of different (hetero)biaryls using these catalysts and highlight their potential applications in the production of biologically active compounds and electronic materials. The study also examines the impact of various phosphine ligands on the polymerization of thiophenes and phenylenes. The results demonstrate that the nickel thiocyanate complexes are effective catalysts for cross-coupling polymerization reactions. These complexes are stable and easy to prepare, making them suitable for various syntheses and polymerizations. [Extracted from the article]

A series of N,N-dimethylaminoalkylamides of perfluorobutanoic and perfluoropentanoic acids were prepared, and the activity of these amides in curing of ED-20 commercial epoxy resin was studied. Data of differential thermal analysis and Fourier IR spectroscopy, taking into account the gel fraction content of the cured composites, show that the curing agent reactivity increases with an increase in the weight fraction of the hydrocarbon moiety and with a decrease in its fluorine content. Evaluation of the adhesion strength in gluing St.3 steel with amide-cured ED-20 epoxy resin shows that all the compounds synthesized ensure two times more efficient gluing compared to the resin cured with the standard curing agent, polyethylenepolyamine. In gluing of D16 aluminum alloy, the gluing efficiency, on the contrary, slightly decreases. [ABSTRACT FROM AUTHOR]

• Metallocenes helped understanding heterogeneous olefin polymerization catalysts. • Bulky cyclopentadienyl ligands were crucial for designing stereospecific catalysts. • Polymerization catalysts for larger monomers require half-sandwich complexes. • Chelating cyclopentadienyl complexes can polymerize bulky monomers. This personal account summarizes the development of molecularly defined organometallic polymerization catalyst precursors based on cyclopentadienyl metal complexes. Departure from the bent metallocene structure provided opportunities to considerably expand the coordination sphere of early transition metal centers relevant to olefin polymerization. Thus, half-sandwich metal complexes such as those featuring linked amido-cyclopentadienyl ligands ("constrained geometry catalysts") allowed copolymerization of ethylene with larger comonomers, while mono(cyclopentadienyl) complexes of titanium and rare earth metals offered new opportunities to develop catalysts for the stereoselective polymerization of monomers such as styrene. The quest for molecular understanding of heterogeneous Ziegler-type catalysts has inspired the organometallic chemistry of the early transition metals, initially limited to that of zirconocenes. The importance of modifying cyclopentadienyl ligands for the rational design of homogeneous polymerization catalysts is highlighted. [Display omitted] [ABSTRACT FROM AUTHOR]

Discrimination of single fibers is important in forensic investigation. Conventional microscopic observation and analytical methods such as micro-Fourier transform-infrared spectroscopy, a suitable technique for polymer component identification, can discriminate single white fibers made from different polymers. Polyesters contain metal compounds derived from polymerization catalysts, transesterification catalysts, and matting agents. Here we propose a forensic method for discriminating white-based polyester single fibers. The X-ray intensity ratios, distribution of metal elements, and chemical states are identified by semi-microbeam X-ray fluorescence (XRF) spot analysis, nanobeam XRF imaging, and X-ray absorption fine structure analysis (XAFS) utilizing synchrotron radiation, respectively. The analytical specimens were white-based polyester single fibers from the standard forensic fiber collection (Microtrace LLC, USA) and commercially available polyester products. Semi-microbeam XRF spot analysis detected metallic elements such as Ti, Mn, Co, Ge, and Sb derived from polymerization catalysts, transesterification catalysts, and matting agents. The X-ray intensity ratios of Ti/Mn, Ti/Ge, Ti/Sb, and Mn/Sb were obtained with good reproducibility but those of Ti/Co, Mn/Co, and Co/Sb, which are related to cobalt, were lowly reproducible in some samples. The poor reproducibility of the cobalt-related X-ray intensity ratios was attributed to uneven distributions of the metallic elements in the polyester single fibers, as visualized by nanobeam XRF imaging. The images showing elemental heterogeneity have proven to be good markers for identification. The XAFS results showed that three types of Ti compounds and two types of cobalt compounds are utilized in different applications of polyester single fibers; moreover, the chemical states are useful indices of single-fiber discrimination. [Display omitted] • Discrimination of white-based polyester single fibers. • Visualization of metal catalytic compound distribution in single fibers by nanobeam X-ray fluorescence imaging. • Estimation of metal compounds in single fibers by X-ray absorption fine structure analysis. • First application of X-ray absorption fine structure analysis in forensic science. [ABSTRACT FROM AUTHOR]

Kinetics of activation of methyl and benzyl metallocene precatalysts by benzhydrylium ions, tritylium ions, and triarylborane B(C6F5)3 were measured spectrophotometrically. The rate constants correlate linearly with the electrophilicity parameter E of the benzhydrylium and tritylium ions employed, allowing us to determine the σ-nucleophilicities of the metal-carbon bond of several zirconocenes and titanocenes. Bridging, substitution, metal, and ligand effects on the rates of metal-alkyl bond cleavage (M=Zr, Ti) were studied and structure-reactivity correlations were used to predict the kinetics of generation of metallocenium ions pairs, which are active catalysts in polymerization reactions and are highly electrophilic Lewis acids in frustrated Lewis pair catalysis. [ABSTRACT FROM AUTHOR]

Kinetics of activation of methyl and benzyl metallocene precatalysts by benzhydrylium ions, tritylium ions, and triarylborane B(C6F5)3 were measured spectrophotometrically. The rate constants correlate linearly with the electrophilicity parameter E of the benzhydrylium and tritylium ions employed, allowing us to determine the σ-nucleophilicities of the metal-carbon bond of several zirconocenes and titanocenes. Bridging, substitution, metal, and ligand effects on the rates of metal-alkyl bond cleavage (M=Zr, Ti) were studied and structure-reactivity correlations were used to predict the kinetics of generation of metallocenium ions pairs, which are active catalysts in polymerization reactions and are highly electrophilic Lewis acids in frustrated Lewis pair catalysis. [ABSTRACT FROM AUTHOR]

This review article describes developments in chiral metallocenes as polymerization catalysts focusing on C2 symmetric ansa-zirconocene complexes. Selective synthesis of rac-isomers of ansa-zirconocenes are surveyed. Isospecific polymerizations of propylene catalyzed by chiral zirconocenes are summarized. Advanced series of polymerizations by chiral metallocenes such as asymmetric polymerization and polymerization of polar monomers are also introduced.

A series of half-titanocenes containing 1,3-imidazolidin-2-iminato ligands of type, ( tert -BuC 5 H 4 )TiCl 2 [1,3-R 2 (CH 2 N) 2 C N] [R = t Bu ( 2a ), cyclohexyl (Cy, 2b ), C 6 H 5 ( 2c ), 2,6-Me 2 C 6 H 3 ( 2d ), 2,6- i Pr 2 C 6 H 3 ( 2e )] have been prepared and structures of 2a – d have been determined by X-ray crystallography. Complex 2a showed higher catalytic activity than the Cp analogue ( 1a ) for ethylene polymerization but showed low catalytic activity in ethylene/1-hexene copolymerization under the similar conditions; the 2,6-Me 2 C 6 H 3 analogue ( 2d ) showed moderate catalytic activity for the ethylene/1-hexene copolymerization. The copolymerization with styrene proceeded in a living manner under certain conditions, whereas the other complexes ( 2a – c ) including the Cp analogues, CpTiCl 2 [1,3-R 2 (CH 2 N) 2 C N] ( 1a – d ), showed low catalytic activities and/or afforded a mixture of polymers (copolymer, and homopolymers) under the similar conditions. [ABSTRACT FROM AUTHOR]

Highly accurate (extrapolated CCSD(T)/aug-cc-pwCVQZ) reference energies have been calculated for olefin insertion in a set of simple models for olefin polymerization catalysts, and also for related reactions (hydrogen transfer to metal and to monomer, allyl formation). The model systems cover early (groups 3 and 4, 10 basic systems, 216 geometries) and late (group 10, 3 basic systems, 51 geometries) transition metals. The reference energies were then used to evaluate the performance of 22 commonly used density functionals, as well as several ab-initio methods. Dispersion corrections (either implicit or explicit) are essential in getting the olefin complexation energy right, but are less important for describing further reactions from the olefin π-complex stage on. No functional performs entirely satisfactorily (within ∼1 kcal/mol) for both early and late transition metals. Of the functionals tested, TPSSh-D0 shows the best “across-the-board” performance (important if chemistry involving more than a single metal needs to be described e.g. chain shuttling, bimetallic complexes, bifunctional systems), but M06-2X performs somewhat better specifically for early transition metals. A subsequent benchmark on 21 experimentally known π-coordination enthalpies and barrier heights for early, middle and late TM systems yielded an MAD of 0.60 kcal/mol using our recommended protocol. Finally, we revisited prototypical catalysts systems studied in early computational work, and conclude that insertion of ethene is nearly barrierless for titanocenes, and has a slightly higher barrier for constrained-geometry catalysts and for Zr analogs. [ABSTRACT FROM AUTHOR]

Alkylation of olefin polymerization catalyst precursors with Me 3 Al (or MAO) is a crucial first step in the activation of many polymerization catalysts. However, structures with alkyls and/or halides bridging between aluminium atoms, are known problem cases for DFT methods. We have explored the scope of the problem and possible solutions. The performance of various DFT methods for a range of bridged dimers [H 2 M] 2 (μ-X) 2 and [Me 2 M] 2 (μ-X) 2 (M = Al–Tl, X = H, Me, NMe 2 , OMe, F, Cl) and related compounds was investigated in a systematic fashion. In the absence of reliable experimental data, highly accurate calculated dimerization and complexation energies (extrapolated to the CCSD(T,Full)/aug-cc-pVQZ level of theory: fully correlated Coupled-Cluster Theory with Single and Double and Perturbative Triple excitations) for 26 model systems relevant to Ziegler–Natta catalysis and related chemistry serve as reference. Most functionals (strongly) underestimate the dimerization energy for both electron-deficient (hydride, alkyl) and regular (halide, alkoxide, amide) bridges, and for both main-group and transition metals. To reach “chemical accuracy”, a basis set of VTZ quality (with BSSE correction) or VQZ (without BSSE correction) is recommended, in combination with the M06-2X functional, or with the TPSSTPSS functional plus Grimme's D2 correction. Subsequently, we explored alkylation of olefin polymerization catalyst precursors LTiX 2 (L = bis(cyclopentadienyl), Salan or Salalen) with Me 3 Al to LTiMe 2 . Using our recommended procedure, we find that the process is exergonic for most electronegative groups X (F, Cl, OR, NR 2 ) provided the dimerization energies of Me 3 Al and Me 2 AlX are taken into account. Moreover, alkylation is more exergonic for metallocenes, which we ascribe to the more saturated nature of the Cp 2 M fragment. Alkylation is predicted to be more favourable for amides and alkoxides than for the widely used chloride precursors, and failure to exploit those precursors in catalysis is likely due to kinetic issues caused by steric factors. In particular, employing metal alkoxides or amides with small alkyl groups (OMe, OEt) rather than the commonly used bulky O i Pr and O t Bu groups might yield catalyst precursors that can be activated more easily than chlorides. [ABSTRACT FROM AUTHOR]

Metal NMR shielding and electric-field gradient (EFG) tensors are examined by quantum-chemical calculations for a set of 14 titanium(IV) complexes. Benchmarks are performed for titanocene chlorides that have been characterized recently by solid-state NMR experiments, focusing on the dependence of TiIV NMR parameters on the computational model in terms of the choice of the density functional, and considering molecular clusters versus infinite-periodic solid. Nearest-neighbor and long-range effects in the solid state are found to influence NMR parameters in systems without spatially extended ligands. Bulky ligands increase the fraction of local structure and bonding information encoded in the EFG tensors by reducing intermolecular interactions. Next, Ti shielding constants and EFG tensors for a variety of olefin (co)polymerization catalysts are analyzed in terms of contributions from localized molecular orbitals representing Lewis bonds and lone pairs. Direct links between the observed theoretical trends and the local bonding environment around the Ti metal center are found. A specific dependence of the Ti EFG tensors on the exact arrangement and type of surrounding bonds is demonstrated, providing a basis for further studies on solid-supported titanium catalytic systems. [ABSTRACT FROM AUTHOR]

The 2006 Spring Meeting of the Swiss Chemical Society was held at the University of Fribourg on March 10, 2006. The one-day symposium was dedicated to recent advances in Molecular Functional Materials. The four speakers, Tom Ziegler, Dante Gatteschi, Andrew Holmes and J. Fraser Stoddart covered a wide range of modern functionalized material research.

New rare-earth cymantrenecarboxylate complexes [Ln(μ,η-OCCym)(μ-OCCym)-(η-OCCym)(DMSO)] (Cym = (η-CH)Mn(CO), Ln = Ce ( 1), Nd ( 2), Eu ( 3), Gd ( 4)) were synthesized and characterized by X-ray diffraction. In dimeric structures 1-4, two of four bridging carboxylates are chelating-bridging, and Ln atoms have coordination number 9. The catalytic activity of complex 2 in the polymerization of 2,3-dimethyl-1,3-butadiene was investigated. The thermal decomposition of the synthesized compounds was studied by DSC and TGA. According to the X-ray powder diffraction data, the final thermal decomposition product of 1 in air consists of CeO and MnO. Under the same conditions, complexes 2-4 afford mixtures of LnMnO and MnO. [ABSTRACT FROM AUTHOR]

Abstract: Nanosized ZSM-2 zeolite crystals (∼100nm) with suitable surface acid properties were prepared. ZSM-2 zeolite forms with improved acidity were obtained through thermal deammoniation and steam treatment. Detailed characterization of acidic ZSM-2 zeolite was carried out by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), diffuse reflectance infrared Fourier transform (DRIFT), nitrogen sorptometry, dynamic light scattering (DLS), thermogravimetry (TGA), potentiometric acidity measurements, and FTIR analysis of pyridine adsorption. Acid properties of ZSM-2 zeolite were significantly improved by conversion into its protonated (H-ZSM-2) and dealuminated (DEAL-ZSM-2) forms, in which bridged Si(OH)Al groups with Brönsted acidity (H-ZSM-2) and aluminium extraframework species with Lewis acid character (DEAL-ZSM-2) are generated. These acidic ZSM-2 zeolite forms also maintain adequate crystalline order and high surface area values, making this nanosized zeolite attractive for catalytic applications. In the context of catalyst supporting materials for the polymerization of olefins, the DEAL-ZSM-2 zeolite form showed Lewis acid properties similar to those of a traditional MAO-modified silica support. Thus, DEAL-ZSM-2 zeolite appears as a promising material to be evaluated as polymerization catalyst support when a reduction of the amount of high-cost MAO cocatalyst is desired. [Copyright &y& Elsevier]

The oxygen-linked bis(phenol) 2-oxapropanediyl-1,3-bis(2-tert-butyl-4-methylphenol), [OOO]H2, was prepared in good yield by the condensation of 2-tert-butyl-6-hydroxymethyl-4-methylphenol at 155 °C. This bis(phenol) reacted cleanly with titanium tetrachloride to give the orange titanium dichloro complex [OOO]TiCl2 in virtually quantitative yield. The solubility in pentane indicates a monomeric structure for [OOO]TiCl2 in solution. The reaction of titanium tetra(isopropoxide) gave the di(isopropoxy) complex [OOO]Ti(OiPr)2 which also adopts a monomeric structure of C2v-symmetry in solution. The reaction of the dichloro complex [OOO]TiCl2 with benzyl Grignard reagent in diethyl ether gave the highly light- and air-sensitive, orange dibenzyl complex [OOO]Ti(CH2Ph)2 in good yield. Single crystal X-ray crystallography revealed a penta-coordinate titanium center coordinated to two monohapto benzyl ligands and the tridentate [OOO] ligand in a meridional fashion. The reaction of zirconium tetrabenzyl with [OOO]H2 gave the bis(ligand) complex [OOO]2Zr, regardless of the stoichiometry employed. Crystallographic analysis shows an octahedral coordination geometry with cis-configuration of the two ligands. The compound can be transformed into the dichloro complex [OOO]ZrCl2 by disproportionation with zirconium tetrachloride. Polymerization tests using [OOO]TiCl2 under methylaluminoxane activation revealed moderate polymerization activity towards ethylene and styrene. [Copyright &y& Elsevier]

The sulfur-linked bis(phenol) 2,2′-thiobis(2-tert-butyl-4-methylphenol), tbmpH2, reacted cleanly with titanium tetrachloride to give the orange titanium dichloro complex [Ti(tbmp)Cl2]2 in virtually quantitative yield. Reaction of the dichloro complex [Ti(tbmp)Cl2]2 with methyllithium at low temperature gave the unexpectedly thermally robust, yellow dimethyl complex [Ti(tbmp)Me2]. The reaction of the dichloro complex with benzyl Grignard reagent in pentane afforded the highly crystalline dibenzyl complex [Ti(tbmp)(CH2Ph)2] as a 1,4-dioxane adduct. The single crystal X-ray crystallography revealed a centrosymmetric 1,4-dioxane-bridged molecule that contains two fragments containing six-coordinate titanium centers with the tridentate tbmp ligand in a facial fashion and two η1-benzyl ligands. When [Ti(tbmp)Me2] was activated with B(C6F5)3 in toluene, ethylene was polymerized. [Copyright &y& Elsevier]

Substituted bifunctional phosphorus-based ligands HX(CRR′) n PR″H (or -PR″ 2 ) [where X = O, S, NR′, (substituted) cyclopentadienyl; n = 1, 2, 3; R, R′, R″ = alkyl, aryl, H] were employed as bridging ligands in the synthesis of early/late bridged transition metal complexes. Synthetic routes to the bifunctional ligands were also developed. First, mononuclear complexes, such as [TpZr(OCH 2 PPh 2 ) 3 ] (Tp = trispyrazolylborato), [Cp 2 Zr(1-O-2-PHR-C 6 H 10 )(Me)] (R = 2,4,6-Pr i 3 C 6 H 2 (Tipp)), [Cp 2 Zr(SCH 2 CH 2 PHR) 2 ] (R = Ph, Mes, Tipp), and phosphinoferrocene derivatives, were prepared. These complexes are suitable precursors for the introduction of a second metal (as in, for example, [TpZr(μ-OCH 2 PPh 2 ) 3 Mo(CO) 3 ]). [ABSTRACT FROM AUTHOR]

The synthesis of a new series of iron(II)- and cobalt(II)-based complexes of the general formula M(N∩N∩N)Cl2 (M=Fe; M=Co) bearing 2,6-bis(imin)pyridyl ligands [A–N&z.dbnd6;C–Py–C&z.dbnd6;N–A] that carry bulky, alkyl-free aromatic terminals (A=naphthyl, pyrenyl, 2-benzylphenyl, phenyl) or chiral cycloaliphatic auxiliary moieties (A=((−)-cis-myrtanyl) is described. The Fe(II) complexes are exceptionally active (up to 40800 kg PE/(mol M h) towards the polymerization of ethylene in the presence of methylaluminoxane (MAO) as activator. Varying the steric bulkiness of the aromatic groups in the tridentate ligands affects catalytic productivity, molecular weight and for the first time the microstructure of the resulted material. The Fe(II) precatalysts are an order of magnitude more active than the corresponding Co(II) precatalysts. [Copyright &y& Elsevier]

A semiempirical theoretical method (ICONC) which includes core-core repulsion to the energy terms was used to characterize the 2,2,6,6-tetramethylpiperidine (TMPiP)/MgCl system and the ethyl benzoate (EB)/MgCl system by modeling TMPiP and EB adsorption on the (110) face of β-MgCl. [ABSTRACT FROM AUTHOR]

An Extended Hückel Method (ICONC) which includes core-core repulsion to the energy terms was used to characterize the 2,2,6,6-tetramethylpiperidine (TMPiP)/MgCl system and the ethyl benzoate (EB)/MgCl system by modeling TMPiP and EB adsorption on the (100) face of β-MgCl. [ABSTRACT FROM AUTHOR]