Mechanism of internal rotation in dicarbony(hexaethylbenzene)thiocarbonyl-chromium(0) and cyclopentadienyl(hexaethylbenzene)iron(II) hexafluorophosohate

Abstract

The variable-temperature ¹³C high-field n.m.r. spectrum of (heb)Cr(CO)₂(CS)(1)(heb = hexaethylbenzene)has been shown to be entirely explicable in terms of restricted ethyl group rotation about the arene, and a recent analysis in terms of restricted rotation about the arene–chromium bond cannot therefore be considered conclusive;furthermore, ethyl group rotation in [(heb)Fe(C₅H₅)]PF₆(2), previously claimed as too rapid at accessibly low temperatures for observation by even high-field n.m.r. spectroscopy, is in fact slowed sufficiently at 140K to result in the coexistence of multiple heb stereoisomers in equilibrium.