Theoretical Study of the Mechanism of CO and Acetylene Migratory Insertions into Pt–Cp* Bonds

Density functional theory computation for the reaction of Cp*Pt­(CO)­I with PMe₃ indicates that insertion of CO into the Pt–Cp* bond of Cp*Pt­(CO)­(PMe₃)I proceeds via interaction of a π orbital of Cp* with a π* orbital of CO. A similar pathway is predicted for an insertion reaction of the acetylene complex Cp*Pt­(C₂H₂)­(PMe₃)­I. The conventional mechanism for CO and acetylene insertions, involving direct insertion into the Pt–C bond, is shown to be inoperative in this system

A Mechanistic Investigation of the Gold(III)-Catalyzed Hydrofurylation of C–C Multiple Bonds

The gold-catalyzed direct functionalization of aromatic C–H bonds has attracted interest for constructing organic compounds which have application in pharmaceuticals, agrochemicals, and other important fields. In the literature, two major mechanisms have been proposed for these catalytic reactions: inner-sphere <i>syn</i>-addition and outer-sphere <i>anti</i>-addition (Friedel–Crafts-type mechanism). In this article, the AuCl₃-catalyzed hydrofurylation of allenyl ketone, vinyl ketone, ketone, and alcohol substrates is investigated with the aid of density functional theory calculations, and it is found that the corresponding functionalizations are best rationalized in terms of a novel mechanism called “concerted electrophilic ipso-substitution” (CEIS) in which the gold­(III)-furyl σ-bond produced by furan auration acts as a nucleophile and attacks the protonated substrate via an outer-sphere mechanism. This unprecedented mechanism needs to be considered as an alternative plausible pathway for gold­(III)-catalyzed arene functionalization reactions in future studies

Theoretical Investigation into the Mechanism of Cyanomethylation of Aldehydes Catalyzed by a Nickel Pincer Complex in the Absence of Base Additives

Density functional theory (DFT) was used to study the reaction mechanism of cyanomethylation of aldehydes catalyzed by nickel pincer complexes under base-free conditions. The C-bound cyanomethyl complex, which was initially thought to be the active catalyst, is actually a precatalyst, and in order for the catalytic reaction to commence, it has to convert to the less-stable N-bound isomer. The carbon–carbon bond formation then proceeds via direct coupling of the N-bound isomer and the aldehyde to give a zwitterionic intermediate with a pendant alkoxide function, which is further stabilized by hydrogen-bonding interaction with water molecules (or alcohol product). The N-bound alkoxide group of the zwitterionic intermediate is subsequently substituted by MeCN via an associative mechanism, followed by deprotonation of the coordinated MeCN to afford the final product. It was found that the transition structure for the exchange reaction (substitution of MeCN for the alkoxide group) is the highest energy point on the catalytic cycle, and its energy crucially influences the catalyst efficiency. The Ni complexes ligated by bulky and weak trans-influencing pincer ligands are not appropriate catalysts for the cyanomethylation reaction due to the involvement of very-high-energy transition structures for the exchange reaction. In contrast, benzaldehydes with electron-withdrawing substituents are capable of stabilizing the exchange reaction transition structure due to the increased stability of the zwitterionic intermediate, leading to acceleration of the catalytic reaction