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Cooperative H2 activation at a nickel(0)–olefin centre
Catalytic olefin hydrogenation is ubiquitous in organic synthesis. In most proposed homogeneous catalytic cycles, reactive M–H bonds are generated either by oxidative addition of H 2 to a metal centre or by deprotonation of a non-classical metal dihydrogen (M–H 2 ) intermediate. Here we provide evid...
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Published in: | Nature chemistry 2024-03, Vol.16 (3), p.417-425 |
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Main Authors: | , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Catalytic olefin hydrogenation is ubiquitous in organic synthesis. In most proposed homogeneous catalytic cycles, reactive M–H bonds are generated either by oxidative addition of H
2
to a metal centre or by deprotonation of a non-classical metal dihydrogen (M–H
2
) intermediate. Here we provide evidence for an alternative H
2
-activation mechanism that instead involves direct ligand-to-ligand hydrogen transfer (LLHT) from a metal-bound H
2
molecule to a metal-coordinated olefin. An unusual pincer ligand that features two phosphine ligands and a central olefin supports the formation of a non-classical Ni–H
2
complex and the Ni(alkyl)(hydrido) product of LLHT, in rapid equilibrium with dissolved H
2
. The usefulness of this cooperative H
2
-activation mechanism for catalysis is demonstrated in the semihydrogenation of diphenylacetylene. Experimental and computational mechanistic investigations support the central role of LLHT for H
2
activation and catalytic semihydrogenation. The product distribution obtained is largely determined by the competition between (
E
)–(Z) isomerization and catalyst degradation by self-hydrogenation.
Activation of H
2
by a metal–olefin complex is characterized experimentally and computationally using a nickel pincer complex, showing that the reaction proceeds via a direct ligand-to-ligand hydrogen transfer mechanism. An application of this cooperative H
2
-activation mechanism is demonstrated in the nickel-catalysed semihydrogenation of diphenylacetylene. |
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ISSN: | 1755-4330 1755-4349 |
DOI: | 10.1038/s41557-023-01380-1 |