Computational Methods in Organometallic Catalysis. Yu Lan

Computational Methods in Organometallic Catalysis - Yu Lan


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donate two electrons to its reaction partner for the formation of new covalent bond. Alternatively, an electrophile, which is a molecule with formal unoccupied orbitals, can accept two electrons from its partner for the formation of new covalent bond. Thereinto, coupling reactions could be categorized as redox‐neutral cross‐coupling with an electrophile and a nucleophile, oxidative coupling with two nucleophiles, and reductive coupling with two electrophiles (Scheme 1.1).

Chemical reaction depicts some selected examples of nucleophiles.

      Superficially, at least, the reaction between nucleophile and electrophile could construct a covalent bond undoubtedly. However, the familiar nucleophiles and electrophiles, used in cross‐coupling reactions, are usually inactive, which could not react with each other rapidly. Moreover, when more active nucleophiles and electrophiles are used in coupling reactions, it would become out of control, which would not selectively afford target products. In effect, introducing transition metal catalysis can perfectly solve this problem. The appropriate transition metal can be employed to selectively activate the nucleophiles and electrophiles and stabilize some others, which led to a specially appointed cross‐coupling reaction.

      High‐valence transition metal can obtain electrons from nucleophile, which led to the transformation of nucleophile into electrophile. The newly generated electrophile can couple with other nucleophiles to form covalent bond, which is named oxidative coupling reaction [51–53]. Meanwhile, the reduced transition metal can be oxidized by exogenous oxidant for regeneration. Correspondingly, low‐valence transition metal can donate electrons to electrophile leading to the transformation of electrophile into nucleophile, which can react with another electrophile to form covalent bond. Accordingly, it is named reductive coupling reaction. The oxidized transition metal also can be reduced by exogenous reductant.

      The d orbital of some transition metals could be filled by unpaired electrons, which led to a unique catalytic activity in radical‐involved reactions. The homolytic cleavage of transition metal–carbon (or some other atoms) bond is an efficient way for the generation of a radical species, which can promote further transformations. On the other hand, free radical can react with some transition metal leading to the stabilization of radical, which can cause further radical transformations [54–57]. Moreover, nucleophiles and electrophiles, activated by transition metals, also can react with radical to form new covalent bonds.

      Although there is no electron barrier due to the appropriate symmetry of frontier molecular orbitals, a great deal of uncatalyzed pericyclic reactions would occur under harsh reaction conditions, which could be often attributed to the low‐energy level of highest occupied molecular orbitals (HOMOs) and high‐energy level of lowest unoccupied molecular orbitals (LUMOs) in reacting partners. Transition metals can play as a Lewis acid, which could significantly reduce the LUMO of coordinated organic moiety. Therefore, it has been widely adopted to catalyze pericyclic reactions, which leads to moderate reaction conditions and adjustable selectivity [58–62]. Moreover, the node of d orbital can change the symmetry of a conjugative compound, which involves a transition metal. Therefore, transition metal itself also could participate in a pericyclic reaction to reveal unique catalytic activity.

      1.1.2 A Brief History of Organometallic Chemistry

Schematic illustration of a brief history of organometallic chemistry.

      Source: Based on Didier [63].

      In 1890, Ni(CO)4 was found as the first metal carbonyl complex by L. Mond et al. in the study of the corrosion of stainless steel valves by CO [69]. Next year, Fe(CO)5 was also found by the same


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