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

Crystals of 8-methyl-6,6-diphenyl-5,7-dioxa-8-azonia-6-borata-6,7-dihydro-5H-benzocycloheptene are triclinic, a = 12.917(1), b = 13.285(1), c = 10.567(1) Å, α = 94.183(8), β = 90.094(5), γ = 72.176(6)°, Z = 4, space group . The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.045 and R w = 0.042 for 2914 reflections with I ≥ 2σ(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)OB = 1.559(6), (C)OB = 1.496(3), CB = 1.610(4) Å.