Tunable Binding of Dinitrogen to a Series of Heterobimetallic Hydride Complexes

The reaction of [Ru­(H)2(N2)2(PCy3)2] (1) with β-diketiminate
stabilized hydrides of Al, Zn, and Mg generates a series of new heterobimetallic
complexes with either H2 or N2 ligated to the
ruthenium center. Changing the main-group fragment of the M·Ru-N2 (M = Al, Zn, Mg) complexes can subtly alter
the degree of binding, and therefore activation, of the diatomic ligand,
as evidenced by the νNN absorptions in the
infrared data. Experimental and computational data rationalize this
tunable binding; decreasing the electronegativity of the main group
in the order Al > Zn > Mg infers greater ionic character of
these M·Ru-N2 complexes,
and this in
turn results in greater destabilization of the frontier molecular
orbitals of ruthenium and therefore greater Ru­(4d) → π*­(N2) back-donation.