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

Quantum chemical calculations at the gradient corrected DFT level using the exchange correlation functionals BP86 of the complexes [(dmpe)M(HBR2)] (M = Ni, Pd, Pt; R = Et, Me) are reported. The calculated electronic and molecular structures of the complexes [(dmpe)M(HBR2)] (M = Ni, Pd; R = Et, Me) are consistent with [(dmpe)M(eta(2)-HBR2)] being Ni(0) and Pd(0) complexes in which both hydrogen and boron of the [HBR2] 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(HBEt2)] is a platinum(II) hydride boryl complex rather than a-borane complex, while complex [(dmpe)Pt(HBMe2)] with some residual B-H interaction, is an example of elongated sigma-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(eta(2)-HBMe2)] than in [(dmpe)M(eta(2)-HBEt2)] (M = Ni, Pd). The values of interaction energy, Delta E-int as well as orbital interactions Delta E-orb decrease on going from nickel to palladium. For M-eta(2)-H-BR2 (M = Ni, Pd) bonds, the contribution of electrostatic attractions Delta E-elstat are greater than the orbital interactions, Delta E-orb. The repulsive terms Delta E-Pauli were larger in each case. All four [(dmpe)M(HBR2)] (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(HBR2)] (R = Et, Me), the preparation energy, Delta E-prep as well as interaction energy, Delta E-int and its components, Delta E-pauli, Delta E-elstat, and Delta E-orb are large, since the HBR2 unit near the dissociation limit. The complex [(dmpe)Pt(HBMe2)] is intermediate between sigma-borane complexes and hydride boryl complex. (C) 2007 Elsevier B.V. All rights reserved.