Reactivity Comparison of Primary Aromatic Amines and Thiols in E–H Insertion Reactions with Diazoacetates Catalyzed by Iridium(III) Tetratolylporphyrin

Abstract

A detailed kinetic study is described for the insertion of carbenes from methyl diazoacetate into the N–H bond of aniline, using Ir(TTP)CH3 (TTP = tetratolylporphyrinato) as a catalyst. Aniline strongly coordinates to the Ir center with a binding constant of K = (2.5 ± 0.5) × 104 at 296 K, forming an inactive hexacoordinate complex, (aniline)Ir(TTP)CH3. The rate of N–H insertion is first order in both diazo ester and catalyst. When the true amount of active, five-coordinate Ir(TTP)CH3 is taken into account, the insertion rate is found to be independent of the aniline concentration. This indicates that the rate-limiting step in the catalytic cycle occurs prior to the nucleophilic attack of aniline on an Ir carbene complex to generate a coordinated ylide. Thus, with N–H insertion catalyzed by Ir(TTP)CH3, aniline is both a strong ligand and a potent nucleophile. This is in contrast to the analogous catalytic insertion of carbenes into S–H bonds. p-Toluenethiol is a more weakly binding ligand toward Ir(TTP)CH...