Transition metal carbonyl complexes structure determination

Summary Some recent chemistry of the stable silylenes, (CHNtBu)2Si (1) and (CH2NtBu)2Si (2) is reported [1]. The X-ray crystal structure of 1 has finally been determined. Both silylenes react with transition metal carbonyls to displace CO and form silylene complexes. Complexes of 1 and 2 with Cr, Mo, W, Fe, Ru, and Ni have been prepared and studied structurally. Reactions of 1 and 2 with halocarbons yield either simple addition of the C-X bond to the silylene, or 2 1 silylene halocarbon products containing a Si-Si bond, depending on the halocarbon. Silylene 1 catalyzes the polymerization of nearly all compounds containing carboiHcarbon double or triple bonds. Possible mechanisms are proposed for several of the reactions described above. 

Examples of metal complexes containing linear carbon ligands have been characterized for metals from across the transition series (Tables IX, X, and XI) and the structural forms A-D can generally be differentiated on the basis of an examination of the structural parameters. However, the variable precision of the structure determinations, the different size of the various metals and variations in the electrostatic contribution to the M-C bond with metal oxidation state and the nature of the other supporting ligands (e.g., phosphine vs. carbonyl) make detailed comparisons of the molecular parameters within a structural subset somewhat arbitrary. 

Transition metal catalysts, specifically those composed of iron nanoparticles, are widely employed in industrial chemical production and pollution abatement applications [67], Iron also plays a cracial role in many important biological processes. Iron oxides are economical alternatives to more costly catalysts and show activity for the oxidation of methane [68], conversion of carbon monoxide to carbon dioxide [58], and the transformation of various hydrocarbons [69,70]. In addition, iron oxides have good catalytic lifetimes and are resistant to high concentrations of moisture and CO which often poison other catalysts [71]. Li et al. have observed that nanosized iron oxides are highly active for CO oxidation at low tanperatures [58]. Iron is unique and more active than other catalyst and support materials because it is easily reduced and provides a large number of potential active sites because of its highly disordered and defect rich structure [72, 73]. Previous gas-phase smdies of cationic iron clusters have included determination of the thermochemistry and bond energies of iron cluster oxides and iron carbonyl complexes by Armentrout and co-workers [74, 75], and a classification of the dissociation patterns of small iron oxide cluster cations by Schwarz et al. [76]. 

Protolysis also is a useful way of preparing Z —CO— adducts with the early transition metal centers. Typically, the early transition metal alkyls have carbanionic character and readily react with the acidic metal carbonyl hydrides. In the reaction of Cp2ZrMe2 with CpMo(CO)3H, methane is evolved and Cp2ZrMe2(OC)Mo(CO)2Cp forms (60,61). A low-frequency Z —CO— stretching frequency is observed at 1545 cm - and the formulation is confirmed by an X-ray structure determination. When this complex is placed under a CO atmosphere, a migratory insertion reaction occurs (Scheme 1) to produce a species having both f/2-acetyl and Z —CO— ligands. 

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