Reactions of Organocopper Reagents with the Cationic Bridging Acylium Complex [C₅H₅(CO)Fe]₂(μ-CO)(μ-CHCO)⁺

The bridging acylium complex [C₅H₅(CO)Fe]₂(μ-CO)(μ-CHCO)⁺PF₆^- (2) reacted with organocuprates Li(RCuCN) at the acylium carbon to give the acyl-substituted μ-alkylidene complexes [C₅H₅(CO)Fe]₂(μ-CO)(μ-CHCOR) (6, R = CH₃; 7, R = (CH₂)₃CH₃; 8, R = C₆H₅). The acyl groups of complexes 6–8 display low carbonyl stretching frequencies indicative of strong electron donation from the Fe₂(μ-C) core onto the acyl substituents. The molecular structure of 8, determined by X-ray crystallography, supports these observations. Crystals of 8 are triclinic, space group PI, with a = 7.008 (2) Å, b = 12.392 (3) Å, c = 12.441 (3) Å, α = 118.37 (2)°, β = 91.09 (2)°, γ = 103.42 (2)°, and Z = 2. 6 reacted with CF₃S0₃CH₃ to give the O-methylated complex [C₅H₅(CO)Fe]₂(μ-CO)[μ-CHC(CH₃)OCH₃]⁺CF₃SO₃^- (12) resulting from methylation of the acetyl group of 6 at oxygen. Reaction of 2 with Li₂[(CH₃)₂CuCN] afforded the μ-alkenylidene complex [C₅H₅(CO)Fe]₂(μ-CO)[μ-C=(CH₃)₂] (13) via double nucleophilic addition. 13 reacted with Me₃O⁺BF₄^- to give the μ-alkylidyne complex [C₅H₅(CO)Fe]2(μ-CO)[μ-CC(CH₃)₃]⁺BF4^- (14).