A simple description of the bonding in transition-metal borane complexes

The mechanism of reactivity of transition-metal compounds towards borane complexes (BX 3) was investigated. It was found that the formation of the metal-boron bond required that a pair of electrons must be supplied by the metal and the metal center in the adduct adopted a d n-2configuration. It was also established that protonation of a d nmetal center results in a metal hydride with a d n-2configuration. It was evident that coordination of borane complexes (BX 3) would have the same effect on the d nconfiguration. It was indicated that similarities in oxidation number assignment complicate determination of the d nconfiguration. The formal d nconfiguration is a significant and useful concept in transition-metal chemistry, which can be maintained for compounds that feature σLewis acid ligands.