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 tmpBNP(X) t Bu 2 (X = S, Se), the P oxide (X = O) dimerizes to [tmpBNP(O) t Bu 2 ] 2 ( 5 ) with an eight‐membered flat boat‐shaped B 2 N 2 P 2 O 2 ring. Borane 1 reacts readily with Mel to yield a phosphonium salt 8 and with BBr 3 to give an adduct 9 with a BP bond. In contrast, bis(dichloroboryl)‐methane not only adds to 1 to generate a coordinate BP bond but also chloroborates the BN triple bond, the final product being a new five‐membered heterocycle 10 . Similarly, the BH 3 component of BH 3 ·SMe 2 first adds to the P atom of 1 followed by reaction of a second mol of BH 3 ·SMe 2 which hydroborates the BN 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.