Oxidative addition of an aryl halide to a Rh(I) complex with a PCP pincer ligand

JUAN PELLEGRINO; CECILIA M. GALLEGO; FABIO DOCTOROVICH

CABA

Simposio; Exploring the Frontiers of Chemistry: Challenges for the 21st Century; 2019

Organometallic catalysts have enabled simple preparation routes for obtaining a great variety of organiccompounds, which are used in different areas, such as health, technology, energy, agriculture, etc. Therupture of carbon-halogen (C-X) bonds is frequently a key step in the catalytic formation of C-C bonds. Mostcatalytic cycles consist in a series of elemental steps where several electrons (typically, two) are exchangedbetween a metallic center and its ligands, with oxidative additions (OA) and reductive eliminations being themost representative processes of this kind.In this work, we have studied the oxidative addition reaction of an aryl halide (2-fluoroiodobenzene) with aRh(I) complex with a pincer-type ligand: Rh(PCPt-Bu2) [1], with PCPt-Bu2 (PCP) being 1,3-bis(di-tbutylphosphinomethyl)benzene. Complex [1] was obtained by the reaction between Rh(PCP)(H)(Cl) [0] andthe strong base KHMDS in an Ar atmosphere. In a N2 atmosphere, the resulting product was found to beRh(PCP)(N2). Reduction of [0] in the presence of an aryl halide substrate led to formation of an Rh(I)intermediate which coordinates the substrate(Rh(PCN)(PhX) [2]), which slowly reacts by oxidative addition toyield a Rh(II) complex of the halide, Rh(PCN)(X) [3], as was detected by 1H NMR. The aryl radical thatresults from this reaction then reacts with a benzene molecule from the solvent, and the H? radical resultingfrom this reaction coordinates complex [3] to form Rh(PCN)(H)(X) [4]. This reactivity is unusual for Rh(I)complexes, where the normal product of OA would be the Rh(III) with both the aryl and the halide as ligands.Moreover, the coupling product that results from the aryl radical and the solvent is also relevant for organicsynthesis. By adding excess substrate and base, this reactivity gives place to a catalytic cycle, wherecomplex [4] is again reduced and reacts with excess substrate. Some preliminary studies of this cycle have been performed.