Stereodynamics of ethyl group rotation in co-ordinated hexaethylbenzene: X-ray crystallographic and dynamic n.m.r. spectral studies on dicarbonyl(hexaethyl-benzene)trimethylphosphinechromium(0)

Abstract

The co-ordinated hexaethylbenzene (heb) of (heb)Cr(CO)₂(PMe₃) adopts a 1,2,3,5-distal-4,6-proximal methyl conformation, with an additional distal methyl found as a disorder in the crystal in approximately one molecule in five; the low-temperature n.m.r. spectra of (heb)Cr(CO)₂(PMe₃)(³¹P and ¹³C) are satisfactorily explained by slowed ethyl group rotation resulting in multiple heb steroisomers coexisting in equilibrium and Without invoking slowed rotation about the metal-arene bond.