Research Article

Synthesis of a copper-supported triplet nitrene complex pertinent to copper-catalyzed amination

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Science  13 Sep 2019:
Vol. 365, Issue 6458, pp. 1138-1143
DOI: 10.1126/science.aax4423

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Catching a copper nitrene

Nitrogen typically forms three bonds in its stable compounds. If only one bond is available, the resultant electron-deficient nitrene can react rapidly with hydrocarbons to fill out its valence shell. Metal-stabilized nitrenes have been widely implicated in carbon-nitrogen bond-forming reactions, but the putative intermediates have rarely been synthesized directly. Carsch et al. now report preparation of a copper nitrene complex from an azide precursor. X-ray absorption and diffraction studies support a triplet electronic state that does not engage in multiple bonding with the copper center.

Science, this issue p. 1138


Terminal copper-nitrenoid complexes have inspired interest in their fundamental bonding structures as well as their putative intermediacy in catalytic nitrene-transfer reactions. Here, we report that aryl azides react with a copper(I) dinitrogen complex bearing a sterically encumbered dipyrrin ligand to produce terminal copper nitrene complexes with near-linear, short copper–nitrenoid bonds [1.745(2) to 1.759(2) angstroms]. X-ray absorption spectroscopy and quantum chemistry calculations reveal a predominantly triplet nitrene adduct bound to copper(I), as opposed to copper(II) or copper(III) assignments, indicating the absence of a copper−nitrogen multiple-bond character. Employing electron-deficient aryl azides renders the copper nitrene species competent for alkane amination and alkene aziridination, lending further credence to the intermediacy of this species in proposed nitrene-transfer mechanisms.

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