The oxidation mechanism of dimethylamine borane (DMAB) as a reductant for an electroless deposition
process was studied by an ab initio molecular orbital method. Two types of reaction pathways, via either
three-coordinate borane molecules obtained by primary dehydrogenation reactions, or five-coordinate ones
by primary additions of OH- for the oxidation of the DMAB, were examined. While the former pathway
corresponds to the general oxidation mechanism of the reductant proposed by Meerakker, the present theoretical
results support the latter one. Furthermore, it was clarified that an electron emission occurs when OH- adds
to the four-coordinate compounds, which agrees with the Meerakker's mechanism. Results of the normal-mode analyses showed that the five-coordinate compounds are the transition states. The optimized geometries
of monoanion five-coordinate molecules are nearly bipyramidal. The charge and spin-population analyses
indicated that the axial bondings in the five-coordinate compounds are stabilized by the three-center three- or
four-electron bondings. During the oxidation reaction of the DMAB, the change in the net charge of B is
much smaller than that in the formal oxidation number, which is due to a great covalence. The existences of
the five-coordinate borane molecules, which are first clarified by the present study, could be the key points
of the catalytic activities of the deposited metals.