Reaction of Phosphites with the Electrophilic Allenyl Complex [Fe₂(CO)₆(μ-PPh₂){μ-η¹:η²-(H)C_αC_βC_γH₂}]:  Stepwise Transformation of a μ-η¹:η²-Allenyl into a μ-η¹:η²-Acetylide vs Phosphite Activation

Abstract

Nucleophilic addition of P(OR)3 (R = Me, Et) to the electrophilic allenyl ligand in [Fe2(CO)6(μ-PPh2){μ-η1:η2-(H)CαCβCγH2}] (1) affords the β,γ-unsaturated phosphonate-bridged complexes [Fe2(CO)6(μ-PPh2)(μ-η1:η2-(CH3)CCH{PO(OR)2})], which we suggest result either from an Arbuzov-type dealkylation or a direct nucleophilic attack of water on the phosphorus atom of a zwitterionic phosphonium intermediate. In contrast, in the presence of PhC⋮CLi, which acts to remove extraneous water from the reaction mixture, P−Cα bond formation followed by a 1,3-hydrogen migration gives [Fe2(CO)6(μ-PPh2)(μ-η1:η1-(CH3)CC{P(OR)3})] as the dominant product.