The first example of ethenediolate isomerisation was documented by Evans and co-workers in 1985 (Scheme 14). The cerium ethenediolate ( ) was shown to non-reversibly convert to the more thermodynamically stable trans-isomer (76), over a period of seven months at 100 °C or two weeks at 190 °C under vacuum. Both isomers were fully characterised including by single crystal X-ray analysis.