Theoretical study on interaction of different coordination modes of BH4 ligand with transition metal in [TM(BH4)(CO)4]− (TM = Cr, Mo)

Density functional calculations were performed on bonding and structural features of [(ηn-BH4)TM(CO)4]− (n = 1, 2, 3; TM = Cr, Mo) complexes. Calculations show that the ground state is bidentate which is in good agreement with experimental results. It has been found that the bridge and terminal hydrogen atoms will interchange by two pathways: (i) twist of BH4 about one of the bridge B–H and (ii) twist of BH4 about one of the terminal B–H. The molecular orbital calculations and natural bond orbital methodologies for different isomers of these complexes have been evaluated. The final results indicate that case (i) is more preferable relative to another case.