Structure of monosilylated benzhydroxamic acids in crystals and solutions

O-tert-butyldimethylsilyl (1) and O-tert-butyldiphenylsilyl (2) benzhydroxa mates were prepared and their structure in the solid state was determined b y X-ray diffraction and NMR spectroscopy (N-15, C-13 and Si-29). The soluti on NMR spectra indicate some processes. In chloroform, both compounds isome rize to an equilibrium mixture of hydroxamic (A) and hydroximic (B or C) de rivatives at room temperature. The exact structure of the hydroximic deriva tive could not be determined. The ratio between the isomers is affected by the solvent. In benzene solutions the hydroximic isomer is preferred wherea s in acetonitrile the opposite is true. In dimethylsulfoxide the NMR lines are broad but slow heating to 80 degreesC or above produces disilylated der ivatives of the type Z-O-1,O-4-bis(tert-butyldimethylsilyl)-benzhydroximate . The changes in structure are only partially reversible, the nature of the process responsible for line broadening is not clear. (C) 2001 Elsevier Sc ience B.V. All rights reserved.