Zirconocene hydride reaction with

In a recent study on isobutene polymerization, Bochmann and co-workers examined the reaction of dinuclear, zirconocene hydride initiators with isobutene (and related olefins) at low The final product shown in Scheme 23 results from insertion and C-H activation of 3equiv. of monomer per molecule of dinuclear initiator one of the monomers is hydrogenated in this process. 

However, the course of the reaction can be different in relation with the structure of the starting complexes. For five-membered fused zirconacyclopentenes, zirconacyclohe-xenes(llO) are formed as a 1 1 mixture of diastereomers (Scheme 41). No equilibrium was observed between (110) and zirconocene hydride (111). In comparison, monocychc zirconacyclopentenes and six-membered fused zirconacyclopentenes directly form the product (112), resulting of a /6-hydride transfer/Q -ehmination see a-Elimination) in high yield, presumably via (111). The CG of the fused five-membered ring could be responsible for the absence of /6-hydride transfer see Hydrides). 

Annby, U., Karlsson, S., Gronowitz, S., Hallberg, A., Alvhaell, J., Svenson, R. Hydrozirconation-isomerization. Reactions of terminally functionalized olefins with zirconocene hydrides and general aspects. Acta Chem. Scand. 1993, 47, 425-433. 

Binuclear cationic zirconocene hydrides can be prepared directly from the zirconocene dihydride precursor. Thus, the reaction of the zirconocene dihydride 626 with a trityl borate salt produces the binuclear hydrido complexes 627457 (Scheme 141). The synthesis of 627 may be accompanied by the formation of cationic zirconocene hydrides of higher nuclearity. For example, cationic trinuclear hydrido complex 628 was also isolated during the recrystallization... 

The zirconocene bis(arylamido) complex 787 was obtained by the reaction of Cp2ZrCl2 with 2 equiv. of the lithium amide605 (Scheme 195). When the reaction is carried out in a 1 1 ratio, the monoamide zirconocene chloride is generated as the major product. Reaction of in situ-generated Cp 2Zr with 2-(methylmercapto)aniline yields monoamido zirconocene hydride 788, the spectroscopic data of which suggest an interaction between the S atom and the Zr center in this complex. The bis(amido) complex 787 serves as a precursor for the synthesis of amido rhodium and iridium complexes. 

Usefid reviews address alkyl zirconocene catalysts for the pol)mierisation of silanes to poly silanes by a a-bond metathesis mechanism, chiral titanates as promoters in aldol reactions, and MeTiCl3 as a reagent for chelate-controlled carbonyl addition reactions. 5 xhe reactions of terminally functionalized alkenes with zirconocene hydrides are reviewed. Thermochemical studies show that while the bond dissociation enthalpies of Zr—C6H13 and Zr— CgHjj in zirconocene systems are comparable, the insertion of cyclohexene into the Zr—bond is more exothermic than the insertion of hexene. 

As amply demonstrated by the success of the metathesis reaction [ 127], alkenes and alkynes are synthetically extraordinarily versatile functional groups for transition metal-mediated transformations. Hydrozirconation with readily available zirconocene hydrides allows the direct reductive conversion of... 

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