‘A rendezvous with an old flame’: revisiting olefin hydrogenation with new rhodium and iridium catalysts

Abstract A novel tridentate hemilabile ligand 2 containing phosphine, imine and pyridyl donor groups has been prepared in analogy with the synthesis of the known related ligand 1 . The reaction of 1 or 2 with 〚Rh(COE) 2 Cl〛 2 resulted in the formation of the neutral complexes 〚Rh(L)Cl〛. By a method using 〚M(diene)Cl〛 2 as starting material, cationic complexes of the type 〚M(diene)(L)〛X were also obtained (M = Rh, diene = NBD, L =  1 , 2 ; M = Ir, diene = COD, L =  1 ; X = BF 4 , OTf). A comparative study of the catalytic activity of the new complexes towards the hydrogenation of various olefins has been reported. In particular, the catalysts of the type 〚Rh(L)Cl〛 are remarkably active when prepared in situ, especially for the reduction of hindered olefins.