“…Contributions to this area were reviewed 20 years ago [21], but a few examples are presented here for the purpose of perspective, and also to introduce some recent illustrative results from DFT calculations. For example, while COT, first reported by Willstä tter in 1911 [22], was shown to react with Fe(CO) 5 to give 1, in which the COT is bound as a 1,3-diene, and in which the Fe(CO) 3 unit undergoes a facile peripheral perambulation around the ring [23,24], OFCOT forms the previously mentioned complex 2 in which the coordination mode is quite different and the molecule is non-fluxional [25].…”