Dierk Nanninga

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

Crystals of diphenylboron N-methylacethydroxamate are orthorhombic, a = 12.5478(8), b = 7.8735(3), c = 13.6809(5) A, 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) A.

Borchelate von Salicylaldoxim und Derivaten

Formation and structure of boron chelates of salicylaldoxime are studied with O-alkyloximes and O-acyloximes of salicylaldehyde. The six-membered ring chelates thus obtained are synthesized also by alkylation resp. acylation of the preformed salicylaldoxime boron chelates. Thermolysis of the difluoroboron or diphenylboron chelates gives fluoroboronic resp. phenylboronic acid derivatives of salicylaldoxime that are isolated as dimeric compounds.

Borchelate von salicylaldehydnitronen

Abstract Nitrones of salicylaldehyde react as bidentate ligands with various chelate-forming boron compounds resulting in seven-membered heterocycles with B,N-betaine structure. During the chelate-forming cyclization of the instable intermediate nitrone-adducts of the boron compounds suitable leaving groups from the boron are easily eliminated together with the phenolic proton of the salicylaldehyde moiety.

Nitrone von 2-formylphenylboronsäureestern

Abstract Reactions of 2-formylphenylboronic acid with N-substituted hydroxylamines lead to nitrones which undergo partial anhydride formation at the boronic acid group. The crystallized intermediates of variable composition are converted by esterification with catechol or ethylene glycol into stable defined arylboronate complexes with a cyclic B,N-betaine structure.