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Published on: July 27, 2022
Solvent-Dependent Carbon-to-Metal Hydrogen Atom Transfer Reactivity of a Square Planar Rhodium(II) Alkynyl Complex
Thomas M Hood1, Sophie H Dewick1, Anjali John1
1Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K.
Abstract:
We report on the synthesis and characterization of the square planar rhodium-(II) alkynyl complex [Rh-(PNP-tBu)-(CCtBu)]+ and its transformation into the vinylidene derivative [Rh-(PNP-tBu)-(CCHtBu)]+ by reaction with 9,10-dihydroanthracene. Computational analysis supports a mechanism involving carbon-to-metal hydrogen atom transfer followed by 1,3-hydride migration, and intermediate formation of the associated rhodium-(III) alkynyl hydride [Rh-(PNP-tBu)-H-(CCtBu)]+ has been substantiated experimentally. Study of [Rh-(PNP-tBu)-(CCtBu)]+ in the solid state by EPR spectroscopy, supplemented by multireference CAS-(9,6)/NEVPT2 calculations, enabled assignment as a metal-centered radical to be corroborated, while analysis of frozen glass solutions revealed the presence of square pyramidal solvent adducts of tetrahydrofuran, 2-methyltetrahydrofuran, 1,2-difluorobenzene, fluorobenzene, and α,α,α-trifluorotoluene. Consistent with a carbon-to-metal hydrogen atom transfer mechanism, the extent of solvent coordination measured by EPR spectroscopy inversely correlates with the rate at which the metalloradical reacts with 9,10-dihydroanthracene.
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