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.