FLUXIONALITY OF FE2(CO)4(ETA-C5H5)2 REVISITED

The rate constant k 3 for bridge-terminal CO exchange in the cis-bridged isomer of Fe2(CO)4(CP)2 (1b) is found by C-13 EXSY and DANTE studies to be close to zero at 224 and 234 K, and total band-shape simulations are also consistent with k13 being close to zero at higher temperatures. This result contradicts earner dynamic C-13 NMR studies and implies that the Adams-Cotton pathways to direct bridge-terminal exchange in lb through bridge-opened rotamers have an activation barrier higher than that previously assumed.