Reactions of FeCH2(1+) and CoCH2(1+) with Olefins in the Gas Phase. Studies Involving Olefin Metathesis

Article abstract of DOI:10.1021/ja00295a007

Reactions of the title carbenes with several olefins and alkynes are reported.Ethene reacts with MCH2(1+) yielding exclusively M(1+) formation (C3H6 elimination).Reaction of ethene with MCD2(1+) yields the metathesis products FeCH2(1+) and CoCH2(1+) in 20percent and 2percent yields, respectively.Formation of the metathesis product MC2H4(1+) dominates for propene with no MCH2(1+) produced from MCD2(1+).Formation of MC2H4(1+) is believed to proceed through an ethene-ethylidene intermediate that rearranges to a bis(ethene) complex followed by elimination of ethene.Absence of MCH2(1+) formation from reaction of MCD2(1+) with propene suggests that the alkene-alkylidene conversion is the key step in metathesis of olefins larger than ethene.Several other pathways compete with metathesis such as cyclopropanation, olefin homologation, dehydrogenation, and various C-C bond cleavages.Both carbenes react with butadiene, generating M-c-C5H6(1+) and M-c-C5H5(1+), implying D⁰(Co(1+)-C5H5) > 76+/- 7 kcal/mol and D⁰(Fe(1+)-C5H5) > 87 +/- 5 kcal/mol.Finally, ethyne and propyne react with MCH2(1+) to yield M(1+) as the only product.