SYNTHESIS AND THEORETICAL-ANALYSIS OF PALLADIUM(II) COMPLEXES CONTAINING A ETA(1) METALLACARBYNE LIGAND

Metallacarbyne complexes such as (eta(5)-C5H5)M(CO)(2)=CR (M = MO, W; R = p-Tol) afford simple adduct complexes when reacted with cyclopalladated compounds derived from benzo-(h)quinoline, 8-alkylquinoline, or N,N-dimethylnaphthylamine. The interaction between the metallacarbyne and the palladium atom occurs primarily via the carbyne carbon atom, suggesting a eta(1) interaction between the M=C unit and Pd(II). The bound metallacarbyne is easily displaced by two-electron donor ligands such as pyridine or trialkylphosphines: Comparison of the results of SCF calculations carried out on the [Cp(CO)(2)MoCH]-[PdCl2(NH3)], [Cp(CO)(2)MoCH][AlH3)], and [Cp(CO)(2)MoCHCH3](+) model systems indicates that the bonding between the metallacarbyne and the palladium complex is best described as involving a Lewis acid-Lewis base interaction together with a strong electrostatic component. It is suggested that these adducts are intermediates in the coupling reaction that occurs between the carbyne atom and the palladated carbon atom of the cyclopalladated complexes.