Investigation Into The Scope, Limitations, And Mechanistic Aspects Of A Regioselective Acylation Of Cycloplatinated Complexes

Abstract

In the reaction of N-isopropyl-N-phenyl-2,2'-bipyridin-6-amine with potassium tetrachloroplatinate, the selective C-H bond activation was complicated by the low selectivity of sp² C-H bond activation in acetonitrile and low yield of sp³ C-H activation in acetic acid. The product resulting from the highly selective sp³ activation was collected in low yield due to competing side reactions. Following C[superscript]iPr-N bond dissociation, the platinum complex (2a, X = NH, R = H) was regioselectively acylated. It was later discovered that 2a could be regioselectively acylated by reacting with acetic anhydride in acetic acid. Furthermore, the acylated platinum complex (3a, X = NH, R = H) was also prepared in a cascade intramolecular cycloplatination-acylation reaction by reacting the organic ligand (1a, X = NH, R = H) with potassium tetrachloroplatinate in a mixture of acetic acid and acetic anhydride. A series of ligands with structural modifications have been designed, synthesized, cycloplatinated, and acylated to investigate the scope of this reaction, and to shed light on the mechanism of the acylation. The reaction showed great tolerance to various linker groups (X), as well as many electron donating/withdrawing groups (R) on the phenyl ring. Reaction conditions were optimized and a variety of solvents were useful in this reaction, including acetonitrile, benzonitrile, and 1,2-dichloroethane. Alternate electrophiles such as benzoyl chloride were also useful in the acylation reaction. Experimental results of the acylation reaction of a library of substrates (2) will be reported, and the mechanistic implications of these results will be discussed.