THE STRUCTURE OF 1,2-DIARYL-1,2-BIS(DIMETHYLAMINO)DIBORON COMPOUNDS AND RELATED SPECIES - BORON-NITROGEN ANALOGS OF BUTA-1,3-DIENES

The 1,2-dihalogenodiborane(4) compound Br(Me2N)BB(NMe2)Br 1 reacts with Li(mes) (mes = C6H2-Me3-2,4,6) or LiPh to form the derivatives Br(Me2N)BB(NMe2)(mes) 2, (mes)(Me2N)BB(NMe2)(mes) 3, and the previously reported (synthesised by a different route) species Ph(Me2N)BB(NMe2)Ph 4 in moderate yields. Compounds 2-4 are thermally stable, colourless, crystalline solids. All compounds were characterized by X-ray crystallography and NMR spectroscopy. Their structures have B-B bond lengths that vary from 1.682(16) angstrom in 1 to 1.717(15) angstrom in 3. In addition, all compounds display high angles (from 58.9 to 88.7-degrees) between the planes at the boron atoms and short B-N distances that are near 1.39 angstrom. The structures of 1-4 represent, apparently, the first such acyclic examples for diborane(4) derivatives of the type B2X2(NR2)2 where X = halogen or aryl group. Crystal data: 130 K: 1, Br(Me2N)BB(NMe2)Br, monoclinic, space group P2(1), a = 6.789(2), b = 7.720(2), c = 10.012(4), beta = 103.06(3)-degrees, Z = 2, R = 0.048 for 1109 [l > 2.0-sigma(l)] data; 2, Br(Me2N)BB(NMe2)(mes), monoclinic, space group C2/c, a = 24.890(14), b = 7.662(4), c = 18.500(12), beta = 116.36(4)-degrees, Z = 8, R = 0.063 for 1910 [l > 2.0-sigma(l)] data; 3 (mes)(Me2N)BB(NMe2)(mes), orthorhombic, space group Pbcn, a = 37.983(14), b = 14.167(5), c = 12.282(4) angstrom, Z = 12, R = 0.095 for 1829 [l > 3.0-sigma(l)] data; 4, Ph(Me2N)BB(NMe2)Ph, orthorhombic, space group P2(1)2(1)2(1), a = 8.579(2), b = 12.920(4), c = 13.925(3) angstrom, Z = 4, R = 0.045 for 1776 [l > 4.0-sigma(l)] data.