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Density functional theory (DFT, B3LYP-D3 with implicit solvation in toluene) was used to investigate the mechanisms of olefin hydrosilylation catalyzed by PDI(Fe) (bis(imino)pyridine iron) complexes, where PDI = 2,6-(ArN=CMe)2(C5H3N) with Ar = 2,6-R2-C6H3. We find that the rate-determining step for hydrosilylation is hydride migration from Et3SiH onto the Fe-bound olefin to form (PDI)Fe(alkyl)(SiEt3). This differs from the mechanism for the Pt Karstedt catalyst in that there is no prior Si–H oxidative addition onto the Fe center. (PDI)Fe(alkyl)(SiEt3) then undergoes C–Si reductive elimination to form (PDI)Fe, which coordinates an olefin ligand to regenerate the resting state (PDI)Fe(olefin). In agreement with experimental observations, we found that anti-Markovnikov hydride migration has a 5.1 kcal mol−1 lower activation enthalpy than Markovnikov migration. This system has an unusual anti-ferromagnetic coupling between high spin electrons on the Fe center and the unpaired spin in the pi system of the non-innocent redox-active PDI ligand. To describe this with DFT, we used the “broken-symmetry” approach to establish the ground electronic and spin state of intermediates and transition states over the proposed catalytic cycles. [ABSTRACT FROM AUTHOR]

Abstract: This mini-review covers a series of neutral and ionic group-3 metal and lanthanide complexes bearing two different dianionic fluorenyl-based ligand systems, [Cp–CMe2–Flu]2− and [Me2Si(3,6- t Bu2C13H7)(N t Bu)]2−, which were synthesized upon using of diverse synthetic protocols. Structural aspects and bonding abilities of the fluorenyl ligand in these complexes are discussed, followed by some applications in polymerization and organic catalysis. To cite this article: E. Kirillov et al., C. R. Chimie 9 (2006) . [Copyright &y& Elsevier]

Single-site polymerization catalysts generated in situ via activation of Cp*MMe3 (Cp* = C5Me5; M = Ti, Zr), (CGC)MMe2 (CGC = C5Me4SiMe2NBut; M = Ti, Zr), and Cp2ZrMe2 with Ph3C+B(C6F5)4- catalyze alkylation of aromatic molecules (benzene, toluene) with α-chloronorbornene at room temperature, to regioselectively afford the 1:1 addition products exo-1-chloro-2-arylnorbornane (aryl = C6H5 (1a), C6H4CH3 (1b)) in good yields. Analogous deuterium-labeled products exo-1-chloro-2-aryl-dn-norbornane-7-d¹ (aryl-dn = C6D5 (1a-d6), C6D4CD3 (1b-d8)) are obtained via catalytic arylation of α-chloronorbornene in either benzene-d6 or toluene-d8. Isolated ion-pair complexes such as (CGC)ZrMe(toluene)+B(C6F5)4- and Cp2ThMe+B(C6F5)4- also catalyze the reaction of α-chloronorbornene in toluene-d8 to give 1b-d8 in good yields, respectively. Small quantities of the corresponding bis(1-chloronorbornyl)aromatics 2 are also obtained from preparative-scale reactions. These reactions exhibit turnover frequencies exceeding 120 h-1 (for the Cp*TiMe3/Ph3C+B(C6F5)4--catalyzed system), and chlorine-free products are not observed. Compounds 1 and 2 were characterized by ¹H, 2H, (13)C, and 2D NMR, GC-MS, and elemental analysis. The aryl group exo-stereochemistry in 1a and 1b is established using ¹H-¹H COSY, ¹H-(13)C HMBC, and ¹H-¹H NOESY NMR, and is further corroborated by X-ray analysis of the product 1,4-bis(exo-1-chloro-2-norbornyl)benzene (2a). Control experiments and reactivity studies on each component step suggest a mechanism involving participitation of the metal electrophiles in the catalytic cycle. [ABSTRACT FROM AUTHOR]

This article presents a study, which focuses on structures and reactivity of Zr(IV) chlorobenzene complexes. The structures and reactivity of halocarbon complexes of group 6-11 metals have been studied extensively. Several general reactions have been established for these systems, including substitution of the halocarbon by stronger ligands, C-X oxidative addition, nucleophilic displacement of the activated halide, and X-directed C-H activation.

This contribution describes coordinative/insertive stereoregular homopolymerizations and copotymerizations of styrene and methyl methacrylate (MMA) mediated by a highly active single-site organotitanium catalyst. The catalyst system used to effect these polymerizations of nonpolar and polar olefinic monomers is prepared by in situ Zn reduction of the precursor derived from the reaction (Me[sub5]Cp)TiMe[sub3] + PhaC[sup+]B(C[sub6]F[sub5])[sub4][sup-]. The resulting catalyst produces polystyrene (>95% syndiotactic, 170 000 g/mol molecular weight; s-PS) by the established coordinative/insertive pathway. The same catalyst mediates polymerization of MMA to poly(methyl methacrylate) (>65% syndiotactic, > 70 000 g/mol molecular weight; s-PMMA) by a group transfer protocol-like (GTP-like) pathway (1,4 insertion mechanism). Under optimal conditions, this catalyst also mediates the copolymerization of MMA + styrene (1:19 ratio) at 50 °C to yield random ∼80% coisotactic poly[styrene-co(methyl methacrylate)] (colso-PSMMA) which contains ∼4% MMA. Control experiments argue that a single-site Ti catalyst is the active species for the copolymerization. The catalyst formation process is quite general, and a variety of reducing agents can be substituted for Zn and still effect copolymerization. Control experiments also indicate that known noncoordination copolymerization mechanisms (i.e., ionic or radical) cannot explain this copolymerization. We suggest a new mechanism involving sequential conjugate addition steps to explain these copolymerization results. [ABSTRACT FROM AUTHOR]