Comprehensive Study of the Reactions Between Chelating Phosphines and Ni(cod)2

A comprehensive study of the reactions of chelating phosphines with Ni­(cod)2 to form (phosphine)­Ni­(cod), (phosphine)2Ni, or mixtures thereof is presented. A series of (phosphine)­Ni­(cod) complexes were isolated and characterized. The structural differences between the (phosphine)­Ni­(cod) and (phosphine)2Ni complexes were examined using X-ray crystallography and 1H and 31P NMR spectroscopy. In addition, the effects of ring size, rigidity, and bulk of the phosphine backbone on the formation of either (phosphine)­Ni­(cod) or (phosphine)2Ni were investigated. These studies show that the Ni–P bond lengths in both the (phosphine)­Ni­(cod) and (phosphine)2Ni complexes and the size of the ring formed by the chelating phosphine and Ni are crucial in determining whether or not (phosphine)­Ni­(cod) complexes can be isolated. Other factors such as π-stacking interactions were found to have marginal influence.