Structural studies of organoboron compounds L. 4-(2-Hydroxy-2,2-diphenylacetyl)- 6,6-pentamethylene-2-phenyl-1,3-dioxa-4-aza-2-boracyclohexane and 4-[2,2-difluoro-5,5-bis(4-methoxyphenyl)-1,3-dioxa-2-borata-4-cyclopentylidene]- 6,6-pentamethylene-2-phenyl-1,3-dioxa-4-azonia-2-boracyclohexane

Abstract

The preparation of the organoboron compounds 4-(2-hydroxy-2,2-diphenylacetyl)-6,6-pentamethylene-2-phenyl-1,3-dioxa-4-aza-2-boracyclohexane, 6, 4-(2,2-difluoro-5,5-diphenyl-1,3-dioxa-2-borata-4-cyclopentylidene)-6,6-pentamethylene-2-phenyl-1,3-dioxa-4-azonia-2-boracyclohexane, 14a, and 4-[2,2-difluoro-5,5-bis(4-methoxyphenyl)-1,3-dioxa-2-borata-4-cyclopentylidene]-6,6-pentamethylene-2-phenyl-1,3-dioxa-4-azonia-2-boracyclohexane, 14b, are reported. Crystals of 6 are triclinic, [Formula: see text], a = 8.7348(5), b = 11.0529(6), c = 14.104(1) Å, α = 65.781(5)°, β = 72.147(6)°, γ = 79.928(6)°, Z = 2, ρc = 1.130 g cm−3, and crystals of 14b•1/2 CH2Cl2 are also triclinic, [Formula: see text], a = 11.799(1), b = 13.464(2), c = 10.047(2) Å, α = 103.28(2)°, β = 92.60(2)°, γ = 79.752(8)°, Z = 2, ρc = 1.285 g cm−3. The structures were solved by direct methods and were refined by full-matrix least-squares procedures to final R values of 0.040 and 0.060 for 3881 and 3221 reflections with I ≥ 3σ(I), respectively. Compound 6 has a six-membered cycloboronate structure, bond distances involving the trigonal planar boron atom being (N)O—B = 1.390(2), (C)O—B = 1.345(2), and B—C(phenyl) = 1.557(2) Å. Compound 14b represents a derivative of 6 in which an intramolecularly hydrogen-bonded hydrogen atom has been replaced by a difluoroboron moiety and represents the first structurally characterized compound containing both a phenylboronate and a difluoroboron chelate ring within the same molecule. Bond lengths in 14b involving the trigonal planar boron atom are (N)O—B = 1.403(5), (C)O—B = 1.326(5), and B—C(phenyl) = 1.550(5) Å and those involving the tetrahedral boron atom are O—B = 1.427(5) and 1.547(5), F—B = 1.353(5) and 1.382(5) Å.