A comprehensive study of the reactions of chelating phosphines with Ni(cod) 2 to form (phosphine)Ni(cod), (phosphine) 2 Ni, 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) 2 Ni complexes were examined using Xray crystallography and 1 H and 31 P 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) 2 Ni were investigated. These studies show that the Ni−P bond lengths in both the (phosphine)-Ni(cod) and (phosphine) 2 Ni 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.

A general synthetic route to the first Xantphos nickel alkyne and alkene complexes has been discovered. Various Ni complexes were prepared and characterized. NMR experiments indicate benzonitrile undergoes ligand exchange with a Xantphos ligand of (Xant)2Ni, a compound that was previously believed to be unreactive. The Ni π-complexes were also shown to be catalytically competent in cross coupling and cycloaddition reactions. (Xant)2Ni is also catalytically active for these reactions when activated by a nitrile or coordinating solvent.

A series of (dppf)Ni(ketene) complexes were synthesized and fully characterized. In the solid state, the complexes possess η-(C,O) coordination of the ketene in an overall planar configuration. They display similar structure in solution, except in some cases, the η-(C,C) coordination mode is also detected. A combination of kinetic analysis and DFT calculations reveals the complexes undergo thermal decomposition by isomerization from η-(C,O) to η-(C,C) followed by scission of the C═C bond, which is usually rate limiting and results in an intermediate carbonyl carbene complex. Subsequent rearrangement of the carbene ligand is rate limiting for electron poor and sterically large ketenes, and results in a carbonyl alkene complex. The alkene readily dissociates, affording alkenes and (dppf)Ni(CO). Computational modeling of the decarbonylation pathway with partial phosphine dissociation reveals the barrier is reduced significantly, explaining the instability of ketene complexes with monodentate phosphines.

Electronically variant (dppf)Ni(ketene) complexes were synthesized and characterized to perform kinetic analysis on their decomposition through a decarbonylation/disproportion process to Ni− CO complexes and alkenes. Ligands containing electron-donating groups stabilized such complexes, whereas an electron-withdrawing group was found to destabilize them. Hammett analysis on the decomposition reaction revealed the buildup of negative charges in the rate-determining step, which corroborates past computational models.