Generation of Tricooordinate Boron Anions and Synthetic Use of Novel Boron Compounds

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The generation and reactions of tricoordinate boron anions have been investigated using phosphine-boranes. Tricyclohexylphosphine-monoiodoboranes were reduced by two equivalents of lithium 4,4'-di-tert-butylbiphenylide (LDBB) in tetrahydrofuran at -78ﾟC.The generated chemical species reacted with a variety of electrophiles such as chlorotrimethylsilane, diphenyl disulfide, methyl trifluoromethanesulfonate, ethylene oxide, benzaldehyde, diethyl carbonate, and carbon dioxide to affordphosphine-boranes possessing a sub stituent at the boron atom. Reaction of tri-tert-butylphosphine-monoiodoborane with LDBB,followed by treatment with water or benzyl bromide, provided di-tert-butylphosphine-borane or benzyl (di-tert-butyl) phosphine-borane, respectively. These reactions clearly indicate that tricoordinate boron anions were generated as the reactive intermediates.Phosphine-boranes possessing trifluoromethanesulfonyloxy group at the boron atom were synthesized by treatment of phosphine-borans with trifluoromethanesulfonic acids. The structures of the obtained compounds were unequivocally determined by single crystal X-ray analyzes. These compounds underwent nucleophilic substitution reaction with various nucleophiles such as organocopper reagents to give B-substituted phosphineboranes in good yields.Novel heterocyclic compounds containing P-B-S linkages were also synthesized, and their structures and chemical properties were characterized.