Bonding Situation in “Early‐Late” Transition Metal Complexes Cl 3 M – M ′(PCl 3 ) 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‐ζ quality basis sets have been carried out for the “early‐late” transition metal complexes Cl 3 M – M ′(PCl 3 ) 4 ( M = Ti, Zr, Hf; M ′ = Co, Rh, Ir) and the derivatives R 3 M – M ′L 4 ( R = Cl, NH 2 ; L = PCl 3 , PH 3 , CO). The calculations demonstrate that the metal–metal bond strength in R 3 M – M ′L 4 can be strongly influenced by the nature of the ligands R and L. The intrinsic interaction energy Δ E int and the bond dissociation energy of the M – M ′ bonds in Cl 3 M – M ′(PCl 3 ) 4 are much smaller than in the previously investigated species (H 2 N) 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 Cl 3 M – M ′(PCl 3 ) 4 which have bipyramidal structures have C 3 symmetry. The M –Co bonds in Cl 3 Zr–Co(PCl 3 ) 4 and Cl 3 Hf–Co(PCl 3 ) 4 and to a lesser degree in Cl 3 Ti–Co(PCl 3 ) 4 are unusually long because of direct interactions between the equatorial PCl 3 groups and the group 4 atoms Zr, Hf. The analysis of the metal–metal interactions suggests that Cl 3 M – M ′(PCl 3 ) 4 has M – M ′ single bonds.