26 | December 2021 www.facs.website Yoshiaki Nakao Yoshiaki Nakao studied chemistry at Kyoto University (PhD in 2005 under the tutelage of Profs. Tamejiro Hiyama and Eiji Shirakawa), Yale University (Prof. John F. Hartwig), and the MaxPlanck-Institut für Kohlen- forschung (Prof. Manfred T. Reetz). He has been a faculty member at Kyoto University since 2002 and is currently a full professor. He is interested in developing new reactions, reagents, and catalysts in order to streamline organic synthesis. He has received Mitsui Chemicals Catalysis Science Award of Encouragement in 2009, Merck–Banyu Lectureship Award in 2010, The Chemical Society of Japan Award for Young Chemists in 2011, The Young Scientist’s Prize from the Ministry of Education, Culture, Sports, Science and Technology in 2011, Tetrahedron Young Investigator Award in 2015, Mukaiyama Award in 2017, David Ginsburg Memorial Lectureship in 2018, and JSPS Prize in 2019 among others. Metal catalysis has driven innovation in organic synthesis during the last half-century. An alternative to the traditional strategy of developing catalysts with a single metal center is the combined use of more than one metal complex and design of their cooperative action to achieve new synthetic transformations. With the rich chemistry of metal catalysis that has been developed over the last five decades, as well as recent advancements in organocatalysis and emerging photoredox catalysis, one can imagine that cooperativity of these known catalytic approaches could enable novel synthetic transformations that have been highly challenging via conventional single-site metal catalysis. Cooperative Catalysis for Organic Synthesis By Yoshiaki Nakao https://doi.org/10.51167/acm00020 METAL CATALYSIS IS indispensable in contemporary organic synthesis for the production of useful substances, such as materials and drugs, for modern human life. Many useful metal-catalyzed organic reactions have enabled the cleavage and formation of covalent bonds, which is otherwise challenging, and led to innovation in organic synthesis through providing atom- and step-economical routes to target molecules. The potential of metal catalysts to further unveil novel chemical transformations is infinite because of the different reactivities of the metal elements of the periodic table and the diversity of ligands to finely tune the reactivity of the metal centers. Nevertheless, the development of totally new metal catalysts to allow novel and useful chemical reactions is often laborious. Transition metal complexes show a variety of different types of reactions, such as oxidative addition, transmetalation, olefin insertion, reductive elimination, etc. The reactivity and selectivity of these elemental reactions depend heavily on the electronic and steric features of the metal complexes and can be precisely controlled by their formal oxidative states and the ligands binding to the metal centers. Consequently, a variety of single-metal-based catalysts bearing different transition metals and ligands have been identified to achieve useful reactions such as cross-coupling, olefin metathesis, olefin/ alkyne-functionalization, and oxidation/reduction reactions, among others. These catalytic reactions consist of various elemental reactions such as those mentioned above. For example, the catalytic cycle of Pd-catalyzed cross-coupling reactions can be expressed roughly via three steps: oxidative addition of an electrophile, transmetalation with a nucleophile, and C–C bond-forming reductive elimination (Scheme 1). Each step favors different electronic and steric characteristics with regard to the Pd center. The initial oxidative addition proceeds faster with electron-rich Pd species, and thus electron-donating ligands are favored to make the Pd center nucleophilic, whereas electrophilic Pd(II) undergoes transmetalation efficiently. Although the rate of the reductive elimination step does not usually affect the overall reaction rate, it can be accelerated by ligands with electron-withdrawing π-accepting nature. Accordingly, an optimum catalyst must have well-balanced electronic and steric characteristics to enable the overall catalytic cycle. This may limit the scope of electrophiles and nucleophiles that can participate in the cross-coupling reactions.
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