METAL-COMPLEXES OF HETEROARENES .5. BIS(ETA-6-PHOSPHININE)METAL COORDINATION - IS THERE CONFORMATIONAL PREFERENCE

By means of metal-atom ligand-vapor co-condensation the bis(heteroarene)metal complexes [2,4,6-(t-Bu)3-eta6-phosphinine]2M (M = V, Cr) have been prepared in order to explore the rotamer distribution. Since the tert-butyl groups block rotational interconversion, the original product ratio is conserved over a wide range of temperatures, rendering conformational analysis through magnetic resonance possible. EPR spectra of the vanadium complex and NMR spectra of the chromium analogue both point to a rotamer ratio synclinal:antiperiplanar close to the statistical ratio of 2.1, the deviation from the exact ratio probably stemming from the distorted hexagonal shape of the phosphinine ring. The unequivocal EPR assignment for the individual rotamers of [2,4,6-(t-Bu)3-eta6-C5H2P]V suggests that the parent complex [eta6-C5H5P]2V in rigid solution (DME, 38 K) assumes the antiperiplanar conformation.