Structure and Bonding of the Transition Metal Methyl and Phenyl Compounds MCH₃and MC₆H₅(M = Cu, Ag, Au) and M(CH₃)₂and M(C₆H₅)₂(M = Zn, Cd, Hg)

Quantum mechanical calculations of the geometries and metal—carbon bond dissociation energies using relativistic pseudopotentials with large valence basis sets for the metals are reported for MCH₃and MC₆H₅(M = Cu, Ag, Au) and for M(CH₃)₂and M(C₆H₅)₂(M = Zn, Cd, Hg). The Cu—CH₃bond length calculated at the MP2 level is significantly shorter (1.866 Å) than predicted in most previous studies. This is due to relativistic effects, which are important for accurate calculations of the geometries of copper compounds. The calculated Ag—C(phenyl) bond length (2.091 Å) is much longer than the experimental value of the alleged silver aryl complex (1.902 Å) reported by Lingnau and Strähle (Angew. Chem., Int. Ed. Engl. 1988, 27, 436). The other theoretical bond lengths are in excellent agreement with experimental values. It seems unlikely that the measured compound is a silver aryl complex. The calculated metal—carbon dissociation energies at CCSD(T) are slightly lower than the experimental values. The calculations predict that the M—C bond strengths of the group 11 methyl and phenyl compounds have the order Au > Cu > Ag, while the group 12 elements have the order Zn > Cd > Hg. The NBO method and the topological analysis of the electron density distribution show that the metal-carbon bonds are strongly polarized toward the carbon ends. The M-C polarization decreases from the first to the second and third transition metal rows. The NBO analysis gives only one M-C bond for the M(CH₃)₂and M(C₆H₅)₂compounds. The M—C bonds of the latter compounds are clearly more ionic than the group 11 methyl and phenyl compounds.