Fate of Aryl/Amido Complexes of Rhodium(III) Supported by a POCOP Pincer Ligand: C–N Reductive Elimination, β-Hydrogen Elimination, and Relevance to Catalysis

Abstract

Rhodium complexes supported by the aryl/bis(phosphinite) POCOP pincer ligand undergo reactions that constitute a RhI/RhIII synthetic cycle for C–N coupling analogous to the classical Pd0/PdII Buchwald–Hartwig chemistry. (POCOP)Rh(Ar)(X) complexes (X = Cl, Br) can be readily obtained by oxidative addition of ArX to the (POCOP)Rh fragment generated in situ from (POCOP)Rh(H)(Cl) (1) and NaOtBu. (POCOP)Rh(Ar)(X) complexes react with anilines and diphenylamine in the presence of an equimolar amount of NaOtBu to give RhIII aryl/amido complexes (POCOP)Rh(Ar)(NHAr′) and (POCOP)Rh(Ar)(NPh2). The intermediate (POCOP)Rh(p-F3CC6H4)(OtBu) (7) was isolated and shown to react irreversibly with p-MeC6H4NH2 to give (POCOP)Rh(p-F3CC6H4)(NHC6H4Me-p) (5). The latter undergoes reductive elimination of the diarylamine product p-F3CC6H4NHC6H4Me-p upon heating. The kinetics of this reaction point to a first-order process, and DFT calculations located a transition state for concerted C–N reductive elimination. Complex 1 effected ...