Nitrones and o×imes of bifunctional carbonyl compounds and their reaction products with diarylborinic acids. Crystal and molecular structure of e×amples of five-, si×-, and seven-membered boron chelates

Synthesis has been carried out of diarylboron chelates of 2- and 3-hydroxynitrones, of 2- and 3-hydroxyoximes, and of 2-carboxynitrones and a 2-carboxyoxime. The structures have been determined from spectroscopic data and from X-ray analyses of 5d, 9a, 11b, and 19. Crystals (at 180 K) of 5d are monoclinic, a = 10.543(2), b = 19.085(4), c = 10.2667(3) A, beta = 90.4978(7)%, Z = 4, space group P2(1)/c; those of 9a are orthorhombic, a = 10.9913(5), b = 14.9329(7), c = 10.2460(13) A, Z = 4, space group P2(1)2(1)2(1); those of 11b are monoclinic, a = 11.227(2), b = 9.967(2), c = 17.0537(4) A, beta = 105.4179(5)%, Z = 4, space group P2(1)/n; those of 19 are monoclinic, a = 11.1847(15), b = 13.715(3), c = 11.5559(5) A, beta = 104.8730(10)%, Z = 4, space group P2(1)/n. The structures were solved by direct methods and refined by full-matrix least-squares procedures to R(F, I greater than or equal to 3 sigma>(*) over bar * (I)) = 0.049, 0.047, 0.042, and 0.047, respectively, for CCD data for 5d, 9a, 11b, and 19. The four molecules contain five-, seven-, six-, and five-membered rings, respectively, with O-B-N groups in the 5d, 11b, and 19, and O-B-O in 9a; the rings exhibit various deviations from planarity, particularly the seven-membered ring.