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Ligand Effects in Transition Metal Dihydrogen Complexes: A Theoretical Study 1

1996; American Chemical Society; Volume: 15; Issue: 21 Linguagem: Inglês

10.1021/om9601920

1520-6041

Stefan Dapprich, Gernot Frenking,

Crystallography and molecular interactions

Ab initio calculations at the MP2 and CCSD(T) level of theory using effective core potentials for the heavy atoms have been carried out in order to investigate systematically the trans influence of different ligands L upon H2 coordination in the dihydrogen complexes ML(CO)4(H2) (M = Cr, Mo, W; L = CO, SiO, CS, CN-, NC-, NO+, N2, H-, F-, Cl-, PH3). The optimized geometries and the theoretically predicted M−H2 bond dissociation energies are reported. The ligands L are characterized in terms of their donor and acceptor capability using the CDA partitioning scheme. Strong σ-donor ligands in the trans position enhance the M−H2 bonding, while strong π-acceptors weaken the M−H2 bond. There is a good correlation between the calculated acceptor strength of L and the distance r(H−H) and the M−(H2) bond dissociation energy De, respectively. Finally, the dihydrogen complexes are compared with the related classical hydrides ML(CO)4(H)2.