Contributions to the Chemistry of Boron, 227. The P-centered Chemistry of [(Di-tert-butylphosphanyl)imino]-(2,2,6,6-tetramethylpiperidino)borane

The elements oxygen, sulfur, and selenium add to the P atom of the title borane 1. In contrast to the formation of tmp-B=N-P(X)tBu(2) (X = S, Se), the P oxide (X = O) dimerizes to [tmp-B=N-P(O)tBu(2)](2) (5) with an eight-membered flat boat-shaped B2N2P2O2 ring. Borane 1 reacts readily with Mel to yield a phosphonium salt 8 and with BBr3 to give an adduct 9 with a B-P bond. In contrast, bis(dichloroboryl)methane not only adds to 1 to generate a coordinate B-P bond but also chloroborates the B=N triple bond, the final product being a new five-membered heterocycle 10. Similarly; the BH3 component of BH3 . SMe(2) first adds to the P atom of 1 followed by reaction of a second mol of BH3 . SMe(2) which hydroborates the B=N triple bond. Finally, metal carbonyl fragments add only to the P atom of 1, demonstrating also that the chemistry of the molecule 1 is dominated by the basicity of its P center.