THEORETICAL-STUDY OF TRANSITION-METAL COMPOUNDS WITH MOLYBDENUM-PHOSPHORUS AND TUNGSTEN-PHOSPHORUS TRIPLE BONDS

Quantum mechanical calculations at the HF, MP2, DFT (B3LYP), and CCSD( T) levels of theory using quasirelativistic effective core potentials for the metal and valence basis sets of DZP quality are reported for t he transition metal complexes [M(P)(NH2)(3)] (1, 2), [M(PS)(NH2)(3)] ( 3, 4), [M(P)(NH2)(3)(NH3>)] (5, 6), [M(P)(N3N)] (7, 8; N3N = [(HNCH2CH 2)(3)N](3-)), and [(M(PS)(NH2)(3)(NH3)] (9, 10) with M = Mo, W. The B3 LYP-optimized geometries of 1-10 are in good agreement with experiment . Bond dissociation energies for the LnMP-S bonds calculated at B3LYP an 8-10 kcal/mol higher than the CCSD(T) values. The LnMP-S and M-NH3 bonds of 9 and 10 are predicted to be stronger than the respective bon ds of 3-6. P-31 NMR chemical shifts and the anisotropic components hav e been calculated using the IGLO and GIAO approaches. The results are in accord with experimental data. The bonding situation of the complex es has been analyzed with the help of the NBO partitioning scheme. The phosphido complexes LnMP have metal drop P triple bonds, while the ph osphorus-sulfide complexes have LnM=P=S double bonds. This formally re duces the number of coordination sites at the metal, which explains th e significantly shorter and stronger bond with an amine trans to the M =P=S moiety.