Formation of an Asymmetric Acyclic Osmium−Dienylcarbene Complex

The styryl-allenylidene complex [Os{(E)-CHCHPh}(CCCPh2)(CH3CN)2(PiPr3)2]BF4 (2) reacts with HBF4 to give the styryl-alkenylcarbyne [Os{(E)-CHCHPh}(CCHCPh2)(CH3CN)2(PiPr3)2](BF4)2 (3), which in acetonitrile evolves into the dienylcarbene derivative [Os{C[(E)-CHCHPh]CHCPh2}(CH3CN)3(PiPr3)2](BF4)2 (4) by means of the concerted migration of the styryl ligand from the metal center to the carbyne Cα atom. A kinetic study and DFT calculations on the transformation of 3 into 4 are reported.