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.