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Nitrenium ions as ligands for transition metals

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Abstract

Unlike N-heterocyclic carbenes (NHCs), which are now used ubiquitously in metal-based chemistry, the nitrogen-derived analogue (in which a carbon is replaced with the isoelectronic nitrogen cation, a nitrenium ion) has remained elusive as a ligand for metals. This is especially intriguing, because several other main-group analogues of NHCs have been prepared, and have been shown to coordinate with transition-metal complexes. Here, we describe the preparation of several N-heterocyclic nitrenium ions that are isoelectronic and isostructural to NHCs, and study their ligand properties. The formation of relatively strong nitrenium–metal bonds is unambiguously confirmed, in solution by selective 15N-labelling experiments, and in the solid state by X-ray crystallography. Experimental and computational studies of the electronic properties of this novel type of ligand suggest that they are poor σ-donors and good π-acceptors.

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Figure 1: General representation of N-heterocyclic p-block carbenoids.
Figure 2: Nitrenium-based ligands, complexes and their 15N NMR spectra in solution.
Figure 3: Solid-state structures of 4a and 6 (hydrogen atoms are omitted for clarity).
Figure 4: Preparation of carbonyl complexes 10 and 11 and their solid-state structures.
Figure 5: Electronic characteristics of nitrenium–metal bonding.

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Acknowledgements

The authors acknowledge financial support from the US–Israel Binational Science Foundation (grant no. 2008391), the Israel Science Foundation (grant no. 1292/07) and the FIRST Program of the Israel Science Foundation (grant no. 1514/07). The authors are also grateful to G. Molev for fruitful discussions and D. Milstein for ongoing support.

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Y.T. designed and performed the experiments, and wrote the manuscript. M.A.I. performed the DFT calculations. M.B. collected single-crystal X-ray crystallographic data and solved the structures. M.G. designed and managed the project.

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Correspondence to Mark Gandelman.

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The authors declare no competing financial interests.

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Supplementary information (PDF 479 kb)

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Crystallographic data for compound 4a (CIF 22 kb)

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Crystallographic data for compound 6 (CIF 21 kb)

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Crystallographic data for compound 10a (CIF 21 kb)

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Crystallographic data for compound 11a (CIF 33 kb)

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Tulchinsky, Y., Iron, M., Botoshansky, M. et al. Nitrenium ions as ligands for transition metals. Nature Chem 3, 525–531 (2011). https://doi.org/10.1038/nchem.1068

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