σ-Borane complexes of nickel, palladium and platinum: A theoretical study

Abstract

Quantum chemical calculations at the gradient corrected DFT level using the exchange correlation functionals BP86 of the complexes [(dmpe)M(HBR 2)] (M = Ni, Pd, Pt; R = Et, Me) are reported. The calculated electronic and molecular structures of the complexes [(dmpe)M(HBR 2)] (M = Ni, Pd; R = Et, Me) are consistent with [(dmpe)M(η 2-HBR 2)] being Ni(0) and Pd(0) complexes in which both hydrogen and boron of the [HBR 2] ligands have a bonding interaction with the metal preserving B–H bond character. The results of the theoretical investigation suggest that the complex [(dmpe)Pt(HBEt 2)] is a platinum(II) hydride boryl complex rather than σ-borane complex, while complex [(dmpe)Pt(HBMe 2)] with some residual B–H interaction, is an example of elongated σ-borane complex. The nature of the metal–ligand interactions is quantitatively analyzed with an energy decomposition analysis. The bond dissociation energy is slightly larger in [(dmpe)M(η 2-HBMe 2)] than in [(dmpe)M(η 2-HBEt 2)] (M = Ni, Pd). The values of interaction energy, Δ E int as well as orbital interactions Δ E orb decrease on going from nickel to palladium. For M-η 2-H-BR 2 (M = Ni, Pd) bonds, the contribution of electrostatic attractions Δ E elstat are greater than the orbital interactions, Δ E orb. The repulsive terms Δ E Pauli were larger in each case. All four [(dmpe)M(HBR 2)] (M = Ni, Pd; R = Et, Me) complexes exhibit about 40–44% covalent bonding of the borane ligand to the metal fragment. For the platinum complexes [(dmpe)Pt(HBR 2)] (R = Et, Me), the preparation energy, Δ E prep as well as interaction energy, Δ E int and its components, Δ E Pauli, Δ E elstat, and Δ E orb are large, since the HBR 2 unit near the dissociation limit. The complex [(dmpe)Pt(HBMe 2)] is intermediate between σ-borane complexes and hydride boryl complex.