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(heteroaren e)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 produ ct ratio is conserved over a wide range of temperatures, rendering con formational 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 statist ical ratio of 2.1, the deviation from the exact ratio probably stemmin g from the distorted hexagonal shape of the phosphinine ring. The uneq uivocal EPR assignment for the individual rotamers of [2,4,6-(t-Bu)3-e ta6-C5H2P]V suggests that the parent complex [eta6-C5H5P]2V in rigid s olution (DME, 38 K) assumes the antiperiplanar conformation.