Bromination of Triphenyl Phosphine Borine

Abstract

IN most compounds containing hydrogen linked to boron, the hydrogen atoms have a more or less pronounced electronegative or hydridic character. This is evident in the mildness of the conditions required for their reaction with water or hydrogen chloride to give molecular hydrogen. In the phosphinoborine ring polymers, however, the BH2 groups are exceptionally inert towards hydrolysis. Burg et al. have attributed this to a diminution in the hydridic character of the hydrogen atoms, caused by partial utilization of the B–H bonding electrons in forming π bonds between the boron and phosphorus atoms1–3. Triphenyl phosphine borine, (C6H5)3P.BH3, is another unusually inert boron hydride derivative. Since our preliminary report that it resisted hydrolysis4, we have found that it is not affected by refluxing for 1 hr. with 6 N hydrochloric acid; nor, when dissolved in benzene, does it react with hydrogen chloride gas at room temperature. This stable (m.p. 188°) and easily prepared compound appeals to us as a material with which to investigate the chemical behaviour of deactivated hydrogen atoms attached to boron. We here report the first of a series of experiments by means of which we hope to characterize more fully the type of reactivity possessed by these hydrogen atoms.