Ethylene rotation in chiral octahedral rhenium(I) complexes

A series of complexes of the type [TpRe(CO)(L-D)(eta (2)-ethylene)] has bee n synthesized where Lo is (BuNC)-Bu-t, PMe3, pyridine, 1-methylimidazole, o r NH3 (increasing in electron-donating ability of L-D). The rates of the pr opeller-like rotation of ethylene about the ethylene-rhenium bond have been determined using spin saturation transfer experiments at low temperatures (-85 to -60 degreesC). It was found that the DeltaG(double dagger) values c orrelate with both the C dropO stretching frequencies and Re(II/I) reductio n potentials for these complexes, indicating that the barrier to rotation i s primarily electronic in nature.