Carbon−Carbon Bond Formation between Adjacent Alkenyl Ligands:  η³-Allyl Iridium(III) and η⁴-Butadiene Iridium(I) Complexes from a cis-Bis(alkenyl) Iridium(III) Complex

A carbon−carbon bond is formed between the α-carbons of the alkenyl ligands of the cis-bis(ethenyl)iridium complex [Ir(−CHCH₂)₂(CH₃CN)₂(PPh₃)₂]⁺ (2) to produce the η³-allyl complex [Ir(η³-CH₃CHCHCH₂)(NCCH₃)₂(PPh₃)₂]²⁺ (4) in the reaction of 2 with H⁺, and η⁴-butadiene complexes Ir(η⁴-CH₂CHCHCH₂)(A)(PPh₃)₂ (A = −CHCH-⁺NEt₃ (6), −C⋮CR (7)) in reactions of 2 with terminal alkynes (RC⋮CH; R = H, Ph, and p-C₆H₄CH₃) in the presence of NEt₃. The deuterium labeling experiments suggest an initial attack of H⁺ on the β-carbon of an ethenyl ligand to lead to the C−C bond formation between the α-carbons of the two alkenyl groups of 2 to produce 4.