Closed-shell and open-shell square-planar iridium nitrido complexes.

Coupling reactions of nitrogen atoms represent elementary steps to many important heterogeneously catalysed reactions, such as the Haber-Bosch process or the selective catalytic reduction of NO(x) to give N(2). For molecular nitrido (and related oxo) complexes, it is well established that the intrinsic reactivity, for example nucleophilicity or electrophilicity of the nitrido (or oxo) ligand, can be attributed to M-N (M-O) ground-state bonding. In recent years, nitrogen (oxygen)-centred radical reactivity was ascribed to the possible redox non-innocence of nitrido (oxo) ligands. However, unequivocal spectroscopic characterization of such transient nitridyl {M=N(•)} (or oxyl {M-O(•)}) complexes remained elusive. Here we describe the synthesis and characterization of the novel, closed-shell and open-shell square-planar iridium nitrido complexes IrN(L(t-Bu)) and [IrN(L(t-Bu))] (L(t-Bu)=N(CHCHP-t-Bu(2))(2)). Spectroscopic characterization and quantum chemical calculations for [IrN(L(t-Bu))] indicate a considerable nitridyl, {Ir=N(•)}, radical character. The clean formation of Ir(I)-N(2) complexes via binuclear coupling is rationalized in terms of nitrido redox non-innocence in [IrN(L(t-Bu))].