Synthesis of the new chiral (R)- and (S)-aminodiphosphine ligands sec-butylbis(2-(diphenylphosphino)ethyl)amine, sec-butylbis(2-(dicyclohexylphosphino)ethyl)amine and (alpha-methylbenzyl)bis(2-(dicyclohexylphosphino)ethyl)amine and their organometallic chemistry when combined with iridium

The new chiral aminodiphosphine ligands (R)- and (S)-sec-butylbis(2-(diphenylphosphino)ethyl)amine, (R)- and (S)-sec-butylbis(2-(dicyclohexylphosphino)ethyl)amine and (R)- and (S)-(alpha-methylbenzyl)bis(2-(dicyclohexylphosphino)ethyl)amine have been synthesized from optically pure (R)-(-)- and (S)-(+)-sec-butylamine or (R)-(+)- and (S)-(-)-(alpha-methylbenzyl)amine. The reactions between these PNP* ligands and [Ir(COD)(OMe)](2) have been investigated in either aprotic or protic solvents (COD = cycloocta-1,5-diene). Depending on the substituents at either the carbon stereocenter or the phosphorus donors, iridium products with different structures and/or stabilities are obtained. Among the new complexes, there are monohydride, dihydride, and trihydride species. It is observed that (i) cyclohexyl substituents on the phosphorus donors favor the formation of complexes where the PNP* ligand adopts a meridional conformation; (ii) phenyl groups attached to the carbon stereocenter lead to the formation of thermodynamically stable ortho-metalated products. Irrespective of the phosphorus substituents, this C-H insertion reaction is reversible at room temperature. Both the new ligands and the iridium complexes have been characterized by various chemico-physical techniques, including multinuclear NMR spectroscopy. The structure of the monohydride complex [IrH(COD)(PNP*-5a)] (PNP*-5a = (R)-(-)-sec-butylbis(2-(diphenylphosphino)ethyl)amine) has been determined by single-crystal X-ray diffraction. The PNP*-5a ligand uses only the two phosphorus atoms for coordination, which is completed by a terminal hydride ligand and by the two olefinic ends of a COD molecule.