A Convenient Route to Monoalkyl-Substituted Phosphanylboranes (HRP–BH2–NMe3): Prospective Precursors to Poly[(alkylphosphino)boranes]

A simple method to access borylphosphonium iodides [RH2P–BH2·NMe3]I (1a: R = Me; 1b: R = Et; 1c: R = nPr) by the addition of iodoalkanes to PH2–BH2·NMe3 was developed. Complexes 1a–c were characterized by multinuclear NMR spectroscopy, and 1a and 1b additionally by single-crystal X-ray 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 soluble, low-molecular-mass poly(alkylphosphinoborane) 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[(alkylphosphino)boranes] and are otherwise difficult to access by conventional metal-catalyzed methods.