Fluorination of arylboronic esters enabled by bismuth redox catalysis

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Science  17 Jan 2020:
Vol. 367, Issue 6475, pp. 313-317
DOI: 10.1126/science.aaz2258

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Teaching bismuth to make and break bonds

One major reason why transition metals are good catalysts is that they can shuttle between oxidation states. This flexibility lets them slide in and out of chemical bonds; so, for instance, they can snip a bond between carbon and boron and then stitch a carbonfluorine bond in its place. Planas et al. now report that bismuth can also orchestrate such bond-swapping events. They implement a fully catalytic cycle for fluorination of aryl boronates, in which bismuth hops between its +3 and +5 oxidation states.

Science, this issue p. 313


Bismuth catalysis has traditionally relied on the Lewis acidic properties of the element in a fixed oxidation state. In this paper, we report a series of bismuth complexes that can undergo oxidative addition, reductive elimination, and transmetallation in a manner akin to transition metals. Rational ligand optimization featuring a sulfoximine moiety produced an active catalyst for the fluorination of aryl boronic esters through a bismuth (III)/bismuth (V) redox cycle. Crystallographic characterization of the different bismuth species involved, together with a mechanistic investigation of the carbon-fluorine bond-forming event, identified the crucial features that were combined to implement the full catalytic cycle.

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