Alkyne-to-Vinylidene Transformation on trans-(Cl)Rh(phosphine)2: Acceleration by a Heterocyclic Ligand and Absence of Bimolecular Mechanism

Abstract
Alkyne-to-vinylidene transformation on square-planar trans-(Cl)Rh(phosphine)2 has been proposed to proceed by a mechanism with a key step being bimolecular transfer of hydridic H to an alkynyl carbon. Labeling studies reported here are inconsistent with this pathway. In addition, an imidazolyl substituent accelerates the transformation.