Cyclooctatetraene complexes valence tautomerism

The complex CgHgMo(CO)3 also displays this phenomenon (379a) NMR of this in toluene solution shows a sharp singlet at 70° C, which becomes broadened (half-width 25 cps) at room temperature and freezes to a complex pattern at — 30°C. This is therefore the first known complex of cyclooctatetraene whose proton magnetic resonance shows observable change from rapid to arrested valency tautomerism. 

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