Structural studies of organoboron compounds LXI. Synthesis of (alkylideniminoxy)- diarylboranes and crystal and molecular structure of dimeric (ethylideniminoxy)-bis(4-methoxyphenyl)borane [3,3,6,6-tetrakis(4-methoxyphenyl)-2,5-diethylidene-1,4-dioxa-2,5-diazonia-3,6-diboratacyclohexane]

Oxime diarylborinates, 4, were obtained from several aliphatic and aromatic aldoximes as well as from cyclic ketoximes by acylation with a diarylborinic acid or anhydride (R₂B-X, R = aryl, X = OH or OBR₂). Compounds 4 could also be synthesized by condensation of an (aminoxy)-diarylborane, which supposedly has a cyclodimeric BONBON structure, with an aldehyde or with a ketone. Crystals of 3,3,6,6-tetrakis(4-methoxyphenyl)-2,5-diethylidene-1,4-dioxa-2,5-diazonia-3,6-diboratacyclohexane, 4b, are monoclinic, a = 7.9182(9), b = 19.7582(9), c = 9.6779(8) Å, β = 91.598(8)°, Z = 2, space group P2₁/n. The structure was solved by direct methods and refined by full-matrix least-squares procedures to R = 0.033 and R_w = 0.034 for 2344 reflections with I ≥ 3σ(F²). A dimeric structure featuring a central six-membered BONBON ring has been established for the oxime diarylborinate 4b. This represents the first structurally characterized example of a monocyclic BONBON ring.