Who Wins: Pesci, Peters, or Deacon? Intrinsic Reactivity Orders for Organocuprate Formation via Ligand Decomposition

Abstract

There are three metal-mediated ligand decomposition reactions that give rise to organometallics: (i) decarboxylation of a metal carboxylate, “the Pesci reaction”; (ii) desulfination of a metal sulfinate, “the Peters reaction”; (iii) desulfonation of a metal sulfonate, “the Deacon reaction”. Despite growing interest in their use in applications in organic synthesis, little is known about the relative ease of thermal extrusion of CO 2 versus SO 2 versus SO 3 in metal complexes. Here the intrinsic reactivity orders for organocuprate formation via ligand decomposition have been studied in the gas phase for the first time. A combination of low-energy collision-induced dissociation experiments in an ion trap mass spectrometer and DFT calculations was used. Simple ligand competition experiments in the heterocopper complexes [MeXOCuOYMe] − (where X = CO or SO and Y = SO or SO 2 ), formed via electrospray ionization, show that desulfination occurs more easily than decarboxylation, which in turn is more facile than desulfonation. This is consistent with DFT calculations at the M06/SDD/cc-pVTZ//M06/cc-pVDZ level of theory, which show that the barriers associated with the transition states follow the order SO 2 < CO 2 < SO 3 .