Synthesis and Reactivity of a Transition Metal Complex Containing Exclusively TEMPO Ligands: Ni(η2-TEMPO)2

The reaction of Ni(COD)2 with two equivalents of the TEMPO radical at 68 °C affords the 16 e– “bow-tie” complex Ni(η2-TEMPO)2, 1, in 78% yield. Compound 1 reacts with tert-butyl isocyanide and phenylacetylene at room temperature to yield the 16 e– distorted square planar nickel complexes Ni(η2-TEMPO)(η1-TEMPO)(CNtBu), 2, and Ni(η2-TEMPO)(η1-TEMPOH)(CCPh), 4, respectively. The facile reactivity of 1 is aided by the transition of the TEMPO ligand from an η2 to η1 binding mode. Complex 4 is an unusual example of hydrogen atom transfer from phenylacetylene to a coordinated TEMPO ligand.