Structural studies of organoboron compounds. XXVI. 8-Methyl-6,6-diphenyl-5,7-dioxa-8-azonia-6-borata-6,7-dihydro-5H-benzocycloheptene

Abstract

. Can. J. Chem. 65, 1457Chem. 65, (1987. Crystals of 8-methyl-6,6-diphe~yl-5,7-dioxa-8-azonia-6-borata-6,7-dihydro-5H-be11~0~ycloheptene are triclijc, a = 12.917(1), b = 13.285(1), c = 10.567(1) A, a = 94.183(8), P = 90.094(5), y = 72.176(6)", Z = 4, space group P 1. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.045 and R,,, = 0.042 for 2914 reflections with I 2 2u(I). The envelope-like conformation adopted by the seven-membered chelate ring places one B-phenyl group above the plane of the fused-ring system facilitating a thermally-induced 1,4-migration of a B-phenyl group to the nitrone carbon atom. Mean bond lengths (corrected for libration) are (N)O-B = 1.559 (6)

Structural studies of organoboron compounds. XXXII. 5,5-Difluoro-2,2-pentamethylene-1,4,6-trioxa-3a-azonia-5-borata-1,2,3,4,5,6-hexahydrobenzo[h]azulene and 2,2-pentamethylene-5,5-diphenyl-1,4,6-trioxa-3a-azonia-5-borata-1,2,3,4,5,6-hexahydrobenzo[h]azulene

“…The N-0 bond distances in 6 and 8 (1.369(2) and 1.368(4) A, respectivelylare similar to that observed for the nitrone group in 9 (1.364(3) A) and, as mentioned above for the nitrone c=N+ bond in 9 (22), indicate the increased iminium salt character of the imidate N-oxide group within the B,N-betaine complexes 6 and 8.…”

“…The boron chelates of salicylaldehyde nitrones like 7 or 9, however, do possess the same seven-membered ring skeleton as observed for 6 and 8 (8,22). The structural dimensions of the chelate ring BONCCCO of 9, established by X-ray analysis (22), are strikingly similar to those observed for 6 and 8 (especially so for the latter as expected). The seven-membered chelate ring in 8 has a distorted envelope-like conformation very similar to that observed for 9 while that in 6 has a different conformation, best described as a "twist-envelope" (see Table 5).…”

“…Sevenmembered boron chelates are rare in the literature (8). The boron chelates of salicylaldehyde nitrones like 7 or 9, however, do possess the same seven-membered ring skeleton as observed for 6 and 8 (8,22). The structural dimensions of the chelate ring BONCCCO of 9, established by X-ray analysis (22), are strikingly similar to those observed for 6 and 8 (especially so for the latter as expected).…”

“…22 and references therein), the two 0-B bond lengths in 6 and 8 are significantly different from one another. As is generally the case, the 0-B bonds to the N-oxide oxygen atoms are longer than those to the phenolate 4~ibration corrected bond lengths (esd's assumed equal to those of the uncorrected values) are employed in the discussion and are compared with similarly treated (16) distances unless otherwise stated.…”

Structural studies of organoboron compounds. XXXVII. 8,8-Pentamethylene-6-phenyl-6,9-epoxy-5,7-dioxa-8-azonia-6-borata-6,7,8,9-tetrahydro-5H-benzocycloheptene

“…The BONCO ring in 4 has a distorted half-chair conformation (see Table 4 The seven-membered BONCCCO ring in 4 may be compared with those observed in diphenylboron chelates of salicylaldehyde nitrones (14,15) and certain salicylohydroxamic acid derivatives (16) having the general structure 9. The main difference between these seven-membered rings in 9 and 4, apart from substantial conform$tional differences, is the longer C(7)-N distance in 4 (1.569 A) relative to the corresponding C=N double bond in 9 (1.291 A for the salicylaldonitrone with X = H and R = Me) (15). The N-0 and C(6)-C(7) bonds are also longer in 4.…”