Syntheses and characterizations of linear triborazanes.

Reaction of the amine boranes NH2(R)BH3, where R = H, Me, and Bz, with 1/3 equiv of sodium hexamethyldisilazane produced the five-membered, linear aminoborane anions Na(+)[BH3N(R)HBH2N(R)HBH3(-)], where R = H (1), Me (1Me), and benzyl (1Bz). Reactions of 1 and 1Me with ammonium chloride and methylammonium chloride, respectively, resulted in elimination of NaCl and H2 to produce the linear triborazanes BH3(RNHBH2)2N(R)H2, where R = H (2) and Me (2Me), with the structure of 2 crystallographically confirmed. The reactions of 1 and 1Me with pyridine-HCl produced the pyridine-capped aminoboranes H3B(RNHBH2)2(NC5H5), where R = H (3) and Me (3Me). 2 and 2Me proved to be stable up to 90 °C but produced a mixture of products when heated above 90 °C. 2 was selectively monochlorinated at the terminal boron when treated with 1 equiv of HCl and dichlorinated when reacted with a second 1 equiv of HCl.