The effects of back-bonding to phosphines on the trans influence in [Mo(NH)Cl 3(PR 3) 2] 0,±1 (R  H, Me and F)

Abstract

Approximate density Functional Theory calculations were used to study the trans influence in [Mo(NH)Cl 3(PR 3) 2] 0,±1 (R  H, Me and F complexes. The geometries of the complexes have been fully optimized in the C 2 v point grou The extent of the lengthening of the bond between the metal and the trans chloride relative to the cis chlorides appears to diminish as the electronic occupation of the molybdenum d orbitals is increased from d 0 to d 2. In addition, the angular distortion of the cis ligands away from the imido group also decreases as the metal d orbital occupation increases. These findings are in agreement with structural characterization of related complexes. The reason for the structural changes in these complexes has been identified as back-bonding from the metal to the phosphine σ★ orbitals in the d 2 complexes. The d 2 electrons reside in a molecular orbital that is bonding with respect to metal-phosphine interactions, and anti-bonding with respect to metal- cis chloride interactions. The angular distortion is kept to a minimum in the d 2 complexes in order to maximize the overlap between the metal d xy orbital and the phosphine σ★ orbitals. As a consequence the metal- cis chloride bonds lengthen. The bonding energies between the [Mo(NH)Cl 3] − and (PR 3) 2 fragments have been calculated. The extent of back-bonding to the phosphines has been determined to be greatest when the phosphine is PF 3. Inclusion of d polarization in the phosphorus basis set slightly increases the extent of back-bonding to the phosphines.