Synthesis and X-ray crystal structure of the dimolybdenum acetaldehyde complex [Mo2(η-MeCHO)(CO)4(η-C5H5)2]

Abstract

The reaction of [Mo(MeCHO)(CO)₂(η-C₅H₅)]^–1 with [C₇H₇][BF₄] gives the three organometallics [Mo₂(µ-η²-MeCHO)(CO)₄(η-C₅H₅)₂]2, [{Mo(CO)₃(η-C₅H₅)}₂] and [Mo(CO)₂(η³-C₇H₇)(η-C₅H₅)], the first of which has been characterised by X-ray crystallography [monoclinic, space group P2₁/c, a= 8.265(4), b= 15.191(13), c= 13.511(9)Å, β= 97.89(5)°, R 0.0362 for 2104 independent reflections for which I/σ(I) > 3.0]. The molecule consists of two Mo(CO)₂(η-C₅H₅) groups linked by a Mo–Mo bond [2.9670(8)Å] and bridged by an acetaldehyde ligand (η² through both C and O to one metal atom, σ through the oxygen to the second metal). The same three products arise in the reaction of 1 with [Mo(CO)₃(η-C₇H₇)][BF₄], together with [{Mo(CO)₃(η⁶-C₇H₇)}₂]. Addition of LiBEt₃H to [Mo₂(µ-η²-MeCO)(CO)₄(η-C₅H₅)₂]BF₄ gives a high yield of 2, as does the reaction of HBF₄·OEt₂ with 1. The reaction of complex 1 with any of (CF₃CO)₂O, HCCCH₂Br, PhCH₂Br, [M(CO)₃(η-C₅H₅)][BF₄](M = Mo or W), CH₂Cl₂, [Fe(η-C₅H₅)₂][PF₆] and Fe₂(SO₄)₃ lead to low yields of 2. The tungsten complex [W₂(µ-η²-MeCHO)(CO)₄(η-C₅H₅)₂] is produced in low yield in the reaction of Li[W(H)(COMe)(CO)₂(η-C₅H₅)] with HBF₄·OEt₂.