Regiospecific acylation of cycloplatinated complexes. Scope, limitations, and mechanism.

Abstract

Recently we have discovered a regioselective acylation of cyclometalated platinum complexes in which the cyclometalated platinum complex was selectively acylated by reacting with acetic anhydride in acetic acid. It was further discovered that the acylated complex could also be directly prepared in a cascade intramolecular cycloplatination-acylation reaction by reacting the organic ligand with potassium tetrachloroplatinate in a mixture of acetic acid and acetic anhydride. The scope, limitations and mechanism of this newly discovered reaction were investigated. This was done by designing, synthesizing, cycloplatinating and acylating a series of ligands with structural modifications. Optimization of the reaction conditions indicated that many other solvents such as acetonitrile, benzonitrile, 1,2-dichloroethane, and chlorobenzene could be used in the acylation reaction. The reaction showed great tolerance to various linker groups, as well as many electron donating/withdrawing groups. Based on the mechanistic studies conducted, the most likely mechanism of the acylation reaction involves electrophilic attack at the metalated carbon, platinum migration, and re-aromatization.