The fluxional behaviour of hexaphenylbenzene chromium tricarbonyl: a variable-temperature 13C NMR spectroscopic study

Article abstract of DOI:10.1016/0022-328X(90)85275-4

The 125 MHz 13C NMR spectrum of (C6Ph6)Cr(CO)3 reveals that the metal is ?-bonded to a peripheral ring.At -80 deg.C this chromium-bonded phenyl exhibits slowed rotation on the NMR time-scale and is effectively orthogonal to the central ring.The fluxional process is shown to involve rotation of the Cr(CO)3-complexed phenyl ring; the activation energy barrier is ca. 12.2 kcal mol^-1, a value much lower than those previously reported for non-complexed hexa-aryl benzenes bearing ortho or meta methyl or methoxy substituents.