Density functional theory study on structural isomers and bonding of model complexes M(CO)₅(BH₃·PH₃) (M = Cr, Mo, W) and W(CO)₅(BH₃·AH₃) (A = N, P, As, Sb)

The influence of group 15 various substituents and effect of metal centers on metal-borane interactions and structural isomers of transition metal-borane complexes W(CO)₅(BH₃·AH₃) and M(CO) ₅(BH₃·PH₃) (A = N, P, As, and Sb; M = Cr, Mo, and W), were investigated by pure density functional theory at BP86 level. The following results were observed: (a) the ground state is monodentate, η¹, with C₁ point group; (b) in all complexes, the η¹ isomer with C_S symmetry on potential energy surface is the transition state for oscillating borane; (c) the η² isomer is the transition state for the hydrogens interchange mechanism; (d) in W(CO)₅(BH₃·AH₃), the degree of pyramidalization at boron, interaction energy as well as charge transfer between metal and boron moieties, energy barrier for interchanging hydrogens, and diffuseness of A increase along the series A = Sb < As < P < N; (e) in M(CO)₅(BH₃·PH₃), interaction energy is ordered as M = W > Cr > Mo, while energy barrier for interchanging hydrogens decreases in the order of M = Cr > W > Mo.