THEORETICAL-STUDIES OF ORGANOMETALLIC COMPOUNDS, PART 30 - STRUCTURE AND BONDING OF LOW-VALENT (FISCHER-TYPE) AND HIGH-VALENT (SCHROCK-TYPE) TRANSITION-METAL CARBYNE COMPLEXES

Quantum mechanical ab initio calculations are reported for 13 low-vale nt (Fischer-type) and 13 high-valent (Schrock-type) tungsten carbyne c omplexes. The geometries have been optimized at the HF and MP2 levels of theory with relativistic effective core potentials for the heavy at oms with valence basis sets of DZP quality. Tungsten-carbyne bond diss ociation energies are predicted at CCSD(T) with MP2 optimized geometri es, The electronic structure of the complexes and the metal-ligand bon ding have been analyzed with the help of the NBO method, the topologic al analysis of the electron-density distribution and the CDA method. T he LnW-CR bonds of the Fischer and Schrock carbyne complexes are much stronger than those of related carbene complexes. The strength of the LnW-CR bond is strongly influenced by the nature of R, Substituents wi th p(pi) lone-pair electrons yield lower bond dissociation energies, T his can be explained by a bonding model that uses the (1)Sigma(+) grou nd state of CR+ as reference state for the ligand of the Fischer compl exes and the (4)Sigma(-) excited state of CR as reference state for th e ligand of Schrock complexes.