Article

Boron chelates obtained from salicylaldehyde and 2prime-hydroxyacetophenone azines are colored compounds with potential applications in analytical chemistry. Up to now these complexes have not been studied by X-ray crystallography, although two structures with a six- or a seven-membered chelate ring are possible. This contribution presents the X-ray analysis of 2prime-hydroxyacetophenone azine and its corresponding new mono(diphenylboron) chelate with a six-membered boron heterocyclic ring. With these data structural changes of the ligand on chelate formation and structural differences in comparison to salicylaldehyde azomethine boron chelates are discussed.Key words: boron complex, borinate, azine, azomethine.

Reaction of ketoximes with aliphatic aldehydes and diphenylborinic acid. Crystal and molecular structure of a diphenylboron chelate derived from the pivaldehyde adduct to cyclohexanone oxime

Various ketoximes have been reacted with aliphatic aldehydes in the presence of oxybis(diphenylborane) in order to assess the influence of increasingly bulky residues on the nature of the products. Crystals of 5-tert-butyl-2-cyclohexylidene-3,3-diphenyl-1,4-dioxa-2-azonia-3-boratacyclopentane, 4c, are monoclinic, a = 14.0647(9), b = 11.416(1), c = 14.756(1) Å, β = 115.696(4)°, Z = 4, space group P21/c. The structure was solved by direct methods and refined by full-matrix least-squares procedures to R = 0.038 (Rw = 0.038) for 2511 reflections with I >= 3σ(I). A bulky substituent at the aldehyde favors α-hydroxyalkylation at the oxime oxygen atom and subsequently leads to the formation of BOCON diphenylboron chelates, whereas formaldehyde reacts by N-alkylation of the oximes, resulting in COBON diphenylboron chelates.Key words: ketoximes, organoboron compounds, crystal structure.

Synthesis of C-aryl-N-(2-hydroxyphenylmethyl)-nitrones and their reaction with diphenylborinic or carboxylic acid derivatives. Crystal and molecular structures of a free nitrone ligand and its diphenyl–boron chelate

The syntheses of a number of aromatic aldonitrones of N-(2-hydroxyphenylmethyl)hydroxylamine and their subsequent reactions with diphenylborinic or carboxylic acid derivatives are reported. Crystals of 8-(4-dimethylaminophenylmethylene)-6,6-diphenyl-5,7-dioxa-8-azonia-6-borata-5H-6,7,8,9-tetrahydrobenzocycloheptene, 2b, are triclinic, a = 10.6802(8), b = 11.1809(4), c =10.1520(3) Å, α = 105.847(3)°, β = 92.567(4)°, γ = 84.610(5)°, Z = 2, space group PĪ, and those of C-(4-dimethylaminophenyl)-N-(2-hydroxyphenylmethyl)nitrone, 6e, are monoclinic, a = 12.2319(8), b = 7.071(1), c = 17.2005(9) Å, β = 107.520(4)°, Z = 4, space group P21/a. The structures were solved by direct methods and refined by full-matrix least-squares procedures to R = 0.035 and 0.032 (Rw = 0.036 and 0.032) for 3379 and 1800 reflections with I ≥ 3σ(I), respectively. Compound 2b is representative of a new type of heterocyclic B,N-betaine. The solid state structure of 6e (the precursor to 2b) shows that only small topological changes, but significant changes in the electron distribution, occur upon the formation of the diphenylboron chelate. Keywords: aromatic aldonitrones, organoboron compounds, crystal structures.