COUPLING HAPTOTROPIC SHIFT TO ROTATION BARRIER IN SUBSTITUTED (CYCLOHEXADIENE)ML(N) - A REDOX-INDUCED ROTATION

Rotation about the central CC bond of ethyl-2,6-dioxocyclohexylidene)- 2,5-cyclohexadiene (CHD) has been shown to be possible upon coordinati on of CHD to a metal fragment. The coupling between the rotation about the central CC bond and the haptotropic shift of the CHD ligand to th e metal fragment has been suggested by the earlier experimental studie s and now is confirmed by Extended Huckel calculations. We show how th e energies and shapes of the d orbitals control the coordination mode of the CHD ligand and thus the rotation barrier around the CC bond.