The barrier for the rotation of the alkene about the M-centroid vector is a measure of the strength of the M-alkene pi-bond. Low symmetry complexes are suitable for analysis of these rotational barriers associated with the metal-ethene bond.In CpRh(CH)(CF), the ethene ligand is observed to rotate with a barrier near 12 kcal/mol but no rotation is observed for about the Rh-CF bond.