A convenient route to mono-alkyl substituted phosphanylboranes HRP-BH2- NMe3, prospective precursors to poly(alkylphosphinoboranes)

A simple method is reported for accessing borylphosphonium iodides [RH2P–BH2∙NMe3]I (1a: R = Me, 1b: R = Et, 1c: R = Pr) by the addition of iodoalkanes to PH2–BH2∙NMe3. Complexes 1a-c were characterized by multinuclear NMR spectroscopy, and 1a and 1b were characterized by single crystal Xray diffraction. It was possible to synthesize the Lewis base stabilized organosubstituted phosphanylborane MePH–BH2∙NMe3 (2) from [MePH2–BH2∙NMe3]I (1a). Thermolysis of 2 generated a short and soluble poly(alkylphosphinoborane) polymer (4) consisting of at least 40 repeat units as identified by ESI-MS. These results are promising for the future preparation of a wide range of Lewis base stabilized phosphanylboranes, which are of interest as precursors to poly(alkylphosphinoborane) polymers, which are otherwise difficult to access via conventional metal catalyzed methods.