Crystal and molecular structure of diphenylboron N-methylacethydroxamate (4,5-dimethyl-2,2-diphenyl-1,3-dioxa-4-azonia-2-boratacyclopent-4-ene)

Abstract

Crystals of diphenylboron N-methylacethydroxamate are orthorhombic, a = 12.5478(8), b = 7.8735(3), c = 13.6809(5) Å, Z = 4, space group Pnam. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.037 and Rw = 0.054 for 1265 reflections with I ≥ 3σ(I). The molecule features a five-membered BO2CN ring which lies in the crystallographic mirror plane. The carbon and nitrogen atoms of the heterocyclic ring are positionally disordered. Mean bond lengths (corrected for libration) are: O—B, 1.550(2), B—C, 1.609(2), O—C/N, 1.340(3), C—N, 1.300(2), C/N—CH, 1.470(2), and C—C(phenyl), 1.394(8) Å.

Structural studies of organoboron compounds. XLIII. 4-[(1-Hydroxycyclohexyl)methyl]-2,2,5-triphenyl-1,3-dioxa-4-azonia-2-borata-4-cyclopentene

“…The short C=N distance4 of 1.312(2) A in 4 is similar to the corresponding values of 1.306, 1.300, and 1.309 A reported for 3 (I), 8 (8), and 9 (9), respectively. From plots of T-bond order vs. bond length for C-N bonds (12,13), these distances have T-bond orders between 0.70 and 0.85.…”

“…In contrast to the intramolecular condensation of the phenolic derivative 1 (R = OH) during the reaction with oxybis-(diphenylborane) leading to 3, the benzohydroxamic acid without the phenol function, 1 (R = H), does not give a similar cyclocondensate, 5, stabilization via a seven-membered chelate arrangement like that in 3 no longer being possible. The diphenylboron hydroxamate 4 represents another example of a stable "normal" hydroxamic acid chelate of the diphenylborenium cation (Ph2Bt), like 8 (8), 9 (9), 10 ( l o ) , and others (11).…”

Structural studies of organoboron compounds. XII. Crystal and molecular structures of (acetylacetonato)diphenylboron and (tropolonato)diphenylboron

“…The monoclinic form shown is the mirror image of the molecule described by the coordinates in Table 1 group (which contains C(10) in the triclinic form and C(4) in the monoclinic form). The asymmetric disposition of the phenyl rings in triclinic 1 (and in 2) is that usually observed in Ar2B chelates (1-3,6, 9) while the symmetric disposition observed in monoclinic 1 is less common (5,11). Bond angles at B and 0 atoms, bond distances involving 0 , and chelate ring conformations differ significantly between the two modifications of 1 (see Tables 3-5).…”

Structural studies of organoboron compounds. XVIII. Crystal and molecular structures of 2,2-diphenyl-1,3-dioxa-3a-azonia-2-borataindan and 4-cyclohexyl-6-methyl-2,2-diphenyl-1,3-dioxa-3a-azonia-2-borataindan

“…With the exception of the C(18) methyl substituent in 6b (displacement = 0.008(7) A), all substituents of the pyridine rings are significantly displaced from the mean plane of the ring in the same direction (displacements range from 0.013(1) A for O(2) in 6a to 0.083 (2) A for the same atom in 6b, mean 0.049 A). Unlike the planar five-membered OBONC rings in the closely related molecules 8 (13,14), the analogous rings in 6a and 6b both exhibit non-planar B-envelope conformations, the deviation from planarity being greater in the case of 6b (see Table 5). In view of the chemical similarities between 6 and 8, the non-planarity of the five-membered rings in the present structures is most likely a result of packing forces since intramolecular steric interactions are minimal.…”

“…In view of the B,N-betaine formulation 8 of appeared to be the betaine form 8, based on the analysis of the open-chain hydroxamic acid boron complexes, which has been bond distances which indicate an approximate contribution of verified by X-ray crystallographic analyses of the boron 75% by the resonance structure 8 (13,14). chelates 8 (X = F, Ph) of N-methylacethydroxamic acid (13, No X-ray structure analyses have yet been reported for 14), it was of special interest to determine which of the reso-2-hydroxypyridine N-oxide or for complexes of this ligand (6). nance structures 617 is the major contributor to the resonance The structure of an antibiotic with a comparable ring system4 hybrid.…”