A theoretical study of the complexes formed by monosubstituted phosphines (XH2P) and the methyl radical (CH3) has been carried out by means of MP2 and CCSD(T) computational methods. Two minima configurations have been obtained for each XH2P:CH3 complex. The first one shows small P–C distances and, in general, large interaction energies. It is the most stable one except in the case of the H3P:CH3 complex. The second minimum where the P–C distance is large and resembles a typical weak pnicogen bond interaction shows interaction energies between −9.8 and −3.7 kJ mol–1. A charge transfer from the unpaired electron of the methyl radical to the P–X σ* orbital is responsible for the interaction in the second minima complexes. The transition state (TS) structures that connect the two minima for each XH2P:CH3 complex have been localized and characterized.
