Regioselectivity in the reactions of dimolybdenum and ditungsten σ,η2(4e)-allenylidene complexes with nucleophilic and electrophilic reagents; crystal structure and dynamic behaviour of the cationic complex [W2(η-HC2CMe2)(CO)4(η-C5H5)2][BF4

Abstract

Reaction of the σ,η2(4e)-allenylidene complexes [M2(σ,η2-CCCMe2)(CO)4(η-C5H5)2](M = Mo or W) with K[BHBus3] or HBF4·Et2O results in attack on the γ- or the α-carbon atom forming [M2(σ,η2-CCPri)(CO)4(η-C5H5)2]– and [M2(µ-HC2CMe2)(CO)4(η-C5H5)2]+, respectively; the X-ray crystal structure and solution dynamic behaviour of the cations are discussed in relation to the species [Co3(CCH2)(CO)9]+, and it is shown that the Mo2 cation undergoes an unusual fragmentation reaction on treatment with ButLi.