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 a-carbons of the alkenyl ligands of the cis-bis(ethenyl)iridium complex [Ir(-CH=CH2)(2)(CH3CN)(2)(PPh3)(2)](+) (2) to produce the eta(3)-allyl complex [Ir(eta(3)-CH3CHCHCH2)(NCCH3)(2)(PPh3)(2)](2+) (4) in the reaction of 2 with H+, and eta(4)- butadiene complexes Ir(eta(4)-CH2=CHCH=CH2)(A)(PPh3)(2) (A = -CH=CH-+NEt3 (6), -Cequivalent to CR (7)) in reactions of 2 with terminal alkynes (RCequivalent toCH; R = H, Ph, and p-C6H4CH3) in the presence of NEt3. The deuterium labeling experiments suggest an initial attack of H+ on the beta-carbon of an ethenyl ligand to lead to the C-C bond formation between the alpha-carbons of the two alkenyl groups of 2 to produce 4.