Synthesis of organoborane catalysts for living polymerization of sulfur ylides to produce polymethylene polymers

Organoboranes catalyze the polyhomologation reaction, the repetitive homologation, of dimethylsulfoxonium methylide to afford tris(polymethylene)organoborane polymer architectures. Oxidation of the resultant polymeric organoborane produces ω-hydroxypolymethylene in yields typically ranging from 80–100%. Polymers produced by this method displays a monomodal distribution by gel permeation chromatography with a polydispersity <1.1. The fundamental aspects of this reaction are discussed, including the synthesis of dimethylsulfoxonium methylide and organoboranes, mechanistic studies, and the preparation of high molecular weight polymethylene. The synthesis of ylide complexes with boranes BH₃, BF₃, BPh₃, B(C₆F₅)₃ produced solids that were analyzed by nuclear magnetic resonance, X-ray analysis, and thermal analysis with differential scanning calorimetry and modulated differential scanning calorimetry. The onset temperature of reaction was correlated to the activation energy for 1,2-migration from the solid state for ylide complexes of BH₃, BF₃, B(C₆F₅). The solid-state kinetics of the 1,2-migration for complexes ylide-BPh₃ and B(C ₆F₅)₃ were analyzed by the methods of Kissinger and Doyle. Ligands on boron that prevent polyhomologation along the blocking group, but allow polyhomologation along the remaining primary alkyl groups were explored. Mesityl, tert-butyl, sulfur, and oxygen-containing boranes were explored in the polyhomologation reaction. Alkyl thiaborolanes show selective polyhomologation of the primary alkyl group following two consecutive 1,2-sulfur migrations. Calculations and experiments were used to confirm that B-CH2SMe and B-CH2SPh groups could be used as blocking groups in the polyhomologation reaction. The polyhomologation reaction was applied to the synthesis of a variety of telechelic polymers containing fluorescent groups and biological molecules with molecular weights up to 20,000 and polydispersities <1.1.