G3 molecular orbital calculations predict that the insertions of boron into the CH, NH, and CN bonds of methylamine to form CH2(BH)NH2, CH3N(BH)H, and CH3BNH2 are exothermic by 57.6, 93.9, and 111.8 kcal mol(-1), respectively. However, the addition of atomic boron to the N site of methylamine yeilds a weak additon complex CH3NH2..B, which is lower in energy than the reactants by only 17.2 kcal mol(-1). The dissociation of CH3N(BH)H to CH3 and HNBH has a low activation energy of 28.7 kcal mol(-1) and is the most energetically favored one amomg its three decomposition paths. One of the other two paths yielding the final product CH3NB has a rate-determining step with a high endothermicity of 111.4 kcal mol(-1), but the other leading to CNB has one with a high activation barrier of 105.7 kcal mol(-1) instead. The conversions of CH3BNH2 to the final products CH2BNH and CH2BNH2 are respectively controlled by their endothermicities of 96.9 and 47.7 kcal mol(-1).