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.