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Photosensitized, energy transfer-mediated organometallic catalysis through electronically excited nickel(II)

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Science  27 Jan 2017:
Vol. 355, Issue 6323, pp. 380-385
DOI: 10.1126/science.aal2490

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A nickel's worth of transferred energy

Traditional organic photochemistry often relies on sensitizers, molecules that efficiently absorb light and then transfer the energy to other compounds to spur reactivity. Welin et al. leveraged this approach to stimulate an organometallic nickel catalyst. They photoexcited an iridium complex with blue light. The ensuing energy transfer to nickel enabled C–O bond formation, coupling aryl halides with carboxylic acids. A similar approach could generate a variety of additional reactivity patterns through photosensitized transition metal catalysis.

Science, this issue p. 380

Abstract

Transition metal catalysis has traditionally relied on organometallic complexes that can cycle through a series of ground-state oxidation levels to achieve a series of discrete yet fundamental fragment-coupling steps. The viability of excited-state organometallic catalysis via direct photoexcitation has been demonstrated. Although the utility of triplet sensitization by energy transfer has long been known as a powerful activation mode in organic photochemistry, it is surprising to recognize that photosensitization mechanisms to access excited-state organometallic catalysts have lagged far behind. Here, we demonstrate excited-state organometallic catalysis via such an activation pathway: Energy transfer from an iridium sensitizer produces an excited-state nickel complex that couples aryl halides with carboxylic acids. Detailed mechanistic studies confirm the role of photosensitization via energy transfer.

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