High‐Pressure NMR Studies of [(η3‐C5H5)(η5‐C5H5)Cr(CO)2]. Evidence for Concerted Ring Interchange

Not CO elimination/addition with “ring slippage” but rather a concerted straightening and bending of the two C5H5 rings in 2 is responsible for ring interchange. The reaction was studied by high-pressure 1H and 13C NMR measurements of 1/CO. The activation barrier for the ring interchange is 13.5 ± 1 kcal mol−1. An analysis of the electronic situation in 2 explains this unusual behavior.