| π-Face Donation from the aromatic N-substituent of N-Heterocyclic Carbene Ligands to Metal and Its Role in Catalysis. | |
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MedLine Citation:
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PMID: 22524408 Owner: NLM Status: Publisher |
Abstract/OtherAbstract:
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In this work we calculate the redox potential in a series of Ir and Ru complexes bearing a N-heterocyclic carbene (NHC) ligand presenting different Y groups in the para position of the aromatic N-substituent. The calculated redox potentials excellently correlate with the experimental E1/2 potentials, offering a handle to rationalize the experimental findings. Analysis of the HOMO of the complexes before oxidation suggests that electron donating Y groups destabilizes the metal centered HOMO. Energy decomposition of the metal-NHC interaction indicates that electron donating Y groups reinforce this interaction in the oxidized complexes. Analysis of the electron density in the reduced and oxidized states of representative complexes indicates a clear donation from the Cipso of the N-substituents to an empty d orbital on the metal. In case of the Ru complexes this mechanism involves the Ru-alkylidene moiety. All these results suggest that electron donating Y groups render the aromatic N-substituent able to donate more density to electron deficient metals through the Cipso atom. This conclusion suggests that electron donating Y groups could stabilize higher oxidation states during catalysis. To test this hypothesis we investigated the effect of differently donating Y groups in model reactions of Ru-catalyzed olefin metathesis and Pd-catalyzed C-C cross-coupling. Consistently with the experimental results, calculations indicate an easier reaction pathway if the N-substituent of the NHC ligand presents an electron donating Y group. |
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Authors:
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Raffaele Credendino; Laura Falivene; Luigi Cavallo |
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Publication Detail:
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Type: JOURNAL ARTICLE Date: 2012-4-23 |
Journal Detail:
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Title: Journal of the American Chemical Society Volume: - ISSN: 1520-5126 ISO Abbreviation: - Publication Date: 2012 Apr |
Date Detail:
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Created Date: 2012-4-24 Completed Date: - Revised Date: - |
Medline Journal Info:
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Nlm Unique ID: 7503056 Medline TA: J Am Chem Soc Country: - |
Other Details:
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Languages: ENG Pagination: - Citation Subset: - |
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