Structural studies of organoboron compounds. LVII. Synthesis and structure of bicyclic boron-nitrogen betaines. 1-Methyl-5-(3-nitrophenyl)-4,6,9-trioxa-1-azonia-5-boratabicyclo[3.3.1]nonane and 3,3,4-trimethyl-1-(3-nitrophenyl)-2,6,7-trioxa-3-azonia-1-boratabicyclo[2.2.2]octane

Abstract

The syntheses and structures of the bicyclic boron-nitrogen betaines 1-methyl-5-(3-nitrophenyl)-4,6,9-trioxa-1-azonia-5-boratabicyclo[3.3.1]nonane, 7a, and 3,3,4-trimethyl-1-(3-nitrophenyl)-2,6,7-trioxa-3-azonia-1-boratabicyclo[2.2.2]-octane, 14a, are reported. Crystals of 7a are orthorhombic, a = 20.256(2), b = 37.652(2), c = 6.642(1) Å, Z = 16, space group Fdd2, and those of 14a are orthorhombic, a = 21.402(2), b = 11.334(3), c = 11.248(2) Å, Z = 8, space group Pbca. The structures were solved by direct methods and were refined by full-matrix least-squares procedures to R = 0.038 and 0.045 (Rw = 0.036 and 0.053) for 975 and 1646 reflections with I ≥ 3σ(F2), respectively. The X-ray analyses establish the bicyclo[3.3.1]nonane and bicyclo[2.2.2]octane "cage" structures for 7a and 14a, respectively. Bond lengths involving the tetrahedral boron atom are (N)O—B = 1.519(5), (C)O—B = 1.444(6) and 1.443(6), C(aryl)—B = 1.602(5) Å for 7a; and (N)O—B = 1.530(3), (C)O—B = 1.446(3) and 1.455(3), C(aryl)—B = 1.608(3) Å for 14a. Weak [Formula: see text] interactions are the main feature of the crystal packing arrangements of both compounds.