Bonding Situation in "Early-Late" Transition Metal Complexes Cl3M-M′(PCl3)4 (M = Ti, Zr, Hf; M′ = Co, Rh, Ir) - Theoretical Study for a Ligand Fine Tuning of M-M′ Bonds

Density functional theory calculations using the BP86 functional in combination with triple-xi quality basis sets have been carried out for the "early-late" transition metal complexes Cl3M-M '(PCl3)(4) (M = Ti, Zr, Hf; M ' = Co, Rh, Ir) and the derivatives R3M-M ' L-4 (R = Cl, NH2; L = PCl3, PH3, CO). The calculations demonstrate that the metal-metal bond strength in R3M-M ' L-4 can be strongly influenced by the nature of the ligands R and L. The intrinsic interaction energy Delta E-int and the bond dissociation energy of the M-M ' bonds in Cl3M-M '(PCl3)(4) are much smaller than in the previously investigated species (H2N)(3)M-M '(CO)(4). The M-M ' bonds become stronger in both sets of compounds when the metal atoms become heavier. The equilibrium geometries of Cl3M-M '(PCl3)(4) which have bipyramidal structures have C-3 symmetry. The M-Co bonds in Cl3Zr-Co(PCl3)(4) and Cl3Hf-Co(PCl3)(4) and to a lesser degree in Cl3Ti-Co(PCl3)(4) are unusually long because of direct interactions between the equatorial PCl3 groups and the group 4 atoms Zr, Hf. The analysis of the metal-metal interactions suggests that Cl3M-M '(PCl3)(4) has M-M ' single bonds.