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[BHBu^s₃] 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 Bu^tLi.