N-BONDED TRIAZOLE DERIVATIVES OF BORON - CYCLOTETRAKIS(TRIAZOLYLBORANES)

ASED molecular orbital calculations on the formation of monomeric 1-azolylboranes by the process BH3 + Haz-->H-2 + H2B(az) (Haz = pyrazole, imidazole, 1,2,3-triazole, 1,2,4-triazole, 1,2,5-triazole) indicate that the reaction is energetically favorable and that the charge densities at the nitrogen atoms not involved in bonding to boron are essentially the same as those in the unsubstituted azole. The experimentally observed oligomerizations of 1-triazolylboranes via nonadjacent nitrogen atoms are supported by the calculated data. The oligomerization process is dominated by kinetic rather than thermodynamic factors. The tetrameric 1-triazolylborane [(CH3)2B(ut)]4 (Hut = 1,2,3-triazole, 1a) crystallizes in the monoclinic system in space group C2/c (No. 15) with a = 16.541 (2) angstrom, b = 12.819 (5) angstrom, c = 12.615 (1) angstrom, beta = 105.34 (1)-degrees, and Z = 4 at 296 (1) K. [(CH3)2B(bt)]4 (Hbt = benzotriazole, 1b) crystallizes in the monoclinic system in space group P2(1/c) (No. 14) with a = 9.2125 (9) angstrom, b = 10.282 (2) angstrom, c = 18.897 (3) angstrom, beta = 93.39 (1)-degrees, and Z = 2 at 296 (1) K. The structures are compared with those of several related porphine-like macrocycles, i.e., tetraoxaquaternanes.