AsiaChem | Chemistry in Japan | December 2021 Volume 2 Issue 1

28 | December 2021 www.facs.website Examples of cooperative metal/organo synergistic catalysis are also available as a result of the extensive studies on organocatalysis in the last two decades.11 Krische reported an early example in which a nucleophilic phosphine catalyst was integrated into the intramolecular Pd-catalyzed allylic alkylation reaction (Scheme 4a).12 An intermolecular variant employing an enamine catalyst was then reported by Córdova (Scheme 4b)13. More recently, carbene catalysts have been shown to participate in Pd chemistry to enable the allylic acylation reaction through the reaction of π-allylpalladium with the Breslow intermediate, as demonstrated by Ohmiya and coworkers (Scheme 4c)14. Photoredox catalysis in organic synthesis has been developed significantly in the last ten years.15 This strategy can also be successfully combined with transition metal catalysis to enable highly challenging cross-coupling-type transformations. Molander,16 Doyle, and MacMillan17 pioneered cooperative Ni/Ir photoredox catalysis to achieve novel cross-coupling-type reactions. For example, simple amino acids can participate in the Ni-catalyzed cross-coupling reaction through oxidative decarboxylation to generate radical species, which react with arylnickel intermediates to provide the products upon C–C bond-forming reductive elimination (Scheme 5). Although the proposed catalytic cycle does not involve reaction between two distinct organometallic intermediates, this particular type of cooperative catalysis has found to be highly general to overcome the limitations of cross-coupling chemistry.18 Cooperative double activation catalysis Another effective cooperative catalytic strategy is the use of two metal complexes that react with a single substrate (double activation) to promote bond-cleaving and/or -forming events that are inaccessible or sluggish using a conventional single metal catalyst (Scheme 6a). Scheme 2: The concept behind cooperative synergistic catalysis, and examples of Pd/Cu catalysis. Scheme 3: Other examples of cooperative synergistic metal/ metal catalysis. Scheme 4: Cooperative synergistic Pd/organo catalysis.

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