Dinitrogen-Facilitated Reversible Formation of a Si–H Bond in a Pincer-Supported Ni Complex

Binding of dinitrogen
to transition metal complexes typically involves
coordination to a vacant site or a ligand substitution reaction with
no formal change in oxidation state at the metal. Here, we report
that dinitrogen binding to a PSiP pincer-supported Ni­(II) hydride
results in reduction to a dinuclear Ni(0) bridging dinitrogen complex
containing two Si–H agostic interactions and a monomeric Ni(0)
terminal dinitrogen complex containing a Si–H agostic interaction,
a rare example of dinitrogen facilitating formal reduction at the
metal center and the formation of a Si–H bond. The process
is reversible, and formation of the dinitrogen complexes is enthalpically
driven. DFT calculations support the proposed equilibrium and provide
information about the nature of the bonding in the unusual Ni(0) dinitrogen
complexes. Similar behavior is also observed when CO binds to the
Ni­(II) hydride, but in this case the reaction is irreversible.