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

Abstract

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 NOx to give N2. 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(Lt-Bu)]+ and [IrN(Lt-Bu)] (Lt-Bu=N(CHCHP-t-Bu2)2). Spectroscopic characterization and quantum chemical calculations for [IrN(Lt-Bu)] indicate a considerable nitridyl, {Ir=N}, radical character. The clean formation of IrI–N2 complexes via binuclear coupling is rationalized in terms of nitrido redox non-innocence in [IrN(Lt-Bu)].

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Figure 1: Electron-rich nitrido complexes.
Figure 2: Synthetic scheme.
Figure 3: Molecular and electronic structure of iridium nitrido complexes.
Figure 4: EPR spectroscopic characterization and bonding in [IrN(Lt-Bu)].
Figure 5: Qualitative orbital interactions that lead to N–N coupling.

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Acknowledgements

The authors thank the Deutsche Forschungsgemeinschaft (Emmy-Noether Programm, SCHN950/2-1) and the European Research Council (Grant Agreement 202886) for funding.

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M.G.S. performed and S.S. supervised the synthetic work. M.G.S., B.A., E.J.R., B.d.B. and S.S. carried out the spectroscopic examinations and F.W.H. the crystallographic characterizations. B.d.B. performed the quantum chemical study. The paper was co-written by B.d.B. and S.S. and all the authors discussed the results and commented on the manuscript.

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Correspondence to Bas de Bruin or Sven Schneider.

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The authors declare no competing financial interests.

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Crystallographic data for compound 7b7b (CIF 36 kb)

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Crystallographic data for compound 10 (CIF 32 kb)

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Crystallographic data for compound 11 (CIF 19 kb)

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Scheibel, M., Askevold, B., Heinemann, F. et al. Closed-shell and open-shell square-planar iridium nitrido complexes. Nature Chem 4, 552–558 (2012). https://doi.org/10.1038/nchem.1368

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