Investigation of interactions in Lewis pairs between phosphines and boranes by analyzing crystal structures from the Cambridge Structural Database

The interactions between phosphines and boranes in crystal structures have been investigated by analyzing data from the Cambridge Structural Database (CSD). The interactions between phosphines and boranes were classified into three types; two types depend on groups on the boron atom, whereas the third one involves frustrated Lewis pairs (FLPs). The data enabled geometric parameters in structures to be compared with phosphine–borane FLPs with classical Lewis pairs. Most of the crystal structures (78.1%) contain BH₃ as the borane group. In these systems, the boron–phospho­rus distance is shorter than systems where the boron atom is surrounded by groups other than hydrogen atoms. The analysis of the CSD data has shown that FLPs have a tendency for the longest boron–phospho­rus distance among all phosphine–borane pairs, as well as different other geometrical parameters. The results show that most of the frustrated phosphine–borane pairs found in crystal structures are bridged ones. The minority of non-bridged FLP structures contain, beside phospho­rus and boron atoms, other heteroatoms (O, N, S for instance).