An iridium-mediated C–H activation/CO2-carboxylation reaction of 1,1-bisdiphenylphosphinomethane

Abstract

The reaction of 1,1-bisdiphenylphosphinomethane (dppm, 4 eq.) with [IrCl(coe)₂]₂ results in a solvent dependent equilibrium from which the complexes [IrCl(dppm)(dppm-H)(H)] (1) and [Ir(dppm)₂]Cl (2) were isolated. When 2 is dissolved in methanol, [IrCl(dppm)₂(H)][OCH₃] (4) is formed as dominant species in solution. The C–H activation reaction which leads to 1 and 4 can be suppressed by adding an additional dppm ligand per iridium center resulting in the formation of [Ir(dppm)₃]Cl (5). If the reaction of dppm with [IrX(coe)₂]₂ (X = Cl, I) is performed under an atmosphere of CO₂ the complexes [IrX(dppm)(H){(Ph₂P)₂C–COOH}] (6: X = Cl; 7: X = I) are formed by a CH activation/CO₂ carboxylation sequence. The reaction of 6 with NH₄PF yields [IrCl(dppm)₂(H)]PF₆.(10). Additionally the lithium compounds [Li(dme)₂(dppm-H)] (3) and [Li(dme){(Ph₂P)₂CHCOO}]₂ (8) were prepared for comparison. The molecular structures of the compounds 1, 3, 5, 7, 8 and of the related iridium complex [IrCl(dppm)₂(H)]I (11) are reported.