THE INSERTION OF ACETYLENE INTO THE PALLADIUM CARBON BOND OF SQUARE-PLANAR PD(II) COMPLEXES - A THEORETICAL INVESTIGATION

Ab-initio SCF, CAS-SCF and CI calculations have been carried out for t he acetylene insertion into the Pd-C bond of the [PdCl(NH3)(CH2)(C2H2) ] Model system. The acetylene is found to bind quite weakly to the pal ladium atom and inserts with an activation barrier of 17 kcal mol-1. T he geometry of the transition state corresponds to a monohapto coordin ation of the acetylene. No intermediate seems to be involved on the re action path, at least for the C2H2 system. The effects of substitution of one hydrogen atom by more electron attracting substituents and of a CH group by a metal organic entity are briefly analysed, The stereoc hemical course of the reaction is also investigated in connection with the geometry of the various isomers known for the isolobal C3H5+ orga nic system.