Selective conversion of an ethylene to an ethylidene ligand in reactions of a hydrido(ethylene) complex of tantalum with iodofluorocarbons. Molecular structure of [Ta(η5−C5H5)2(η1−CHCH3)I]

Abstract

Reactions of [TaCp2(C2H4)H] (3) with perfluoro-n-butyl iodide or perfluorobenzyl iodide cleanly yield the iodo(ethylene) complex [TaCp2(C2H4)I] (4) together with the hydrofluorocarbons CF3CF2CF2CF2H and C6F5CF2H, respectively. In sharp contrast, reactions of 3 with perfluoro-iso-propyl iodide or pentafluorophenyl iodide cleanly afford the isomeric iodo(ethylidene) complex [TaCp2(CHCH3)I] (5). No interconversion of 4 and 5 is observed under these reaction conditions, indicating that each is formed under conditions of kinetic control. The structure of 5 has been confirmed by X-ray crystallography. Similar results to give much more thermally sensitive products are observed for the niobium analogues. Possible mechanisms for these highly selective reactions are discussed.