Synthesis and characterization of cationic rhodium complexes of aminophosphine and investigation of their catalytic activity in transfer hydrogenation of ketones

Synthesis and development of new ligands based on P(III) and containing P-N bond have been an important study. Especially, a number of studies on aminophosphine ligands have been carried out for 40 years. Catalytic applications of transition metal complexes of ligands possessing P-N-P and HN-P framework have been attracting considerable interest in industrial process. Their properties, such as attachment of different substituents to P or N atoms, changes in P-N-P or P-NH bond angle and conformational variability on phosphorous atom increase versatility of these ligands. Bidentate bis(phosphine)amine ligands containing P-N-P moiety are more stable than monodentate ligands having HN-P group and have been more studied. However, ligands possessing HN-P moiety are more efficient in catalysis. Furthermore, complexes of these type ligands prepared from a catalytically popular transition metal such as Rh, have been employed in a variety of industrial catalytic processes such as hydrogenation, hydroformylation, allylic alkylation, polymerization, olygomerization. Hydrogenation of aromatic ketones to obtain secondary alcohols is a relatively simple method, whereas transfer hydrogenation of these reactions is more interesting than molecular hydrogenation. Catalytic activities of both cationic Rh(I) and half-sandwich Cp*-Rh(III) complexes of P-N-P based ligands and Rh(I) complexes of HN-P based ligands in transfer hydrogenation of aromatic ketones to secondary alcohols are rather promising. In the present study, firstly, 7 aminophosphine and bis(phosphino)amine ligands were prepared from commercial amines 2-isopropylamine, 4-isopropylamine, 2,6-diisopropylamine 2-thiophenemethylamine and 2-furfurylamine according to the literature. Then, cationic Rh(I) and half-sandwich Cp*-Rh(III) complexes of the bis(phosphino)amines and Rh(I) complexes of NH-P ligands were synthesized. All ligands and complexes were characterized by IR and NMR spectroscopy as well as element analysis. Secondly, catalytic activities of these complexes were investigated in transfer hydrogenation of acetophenone and its derivatives. Key Words: Bis(Phosphino)Amine, Aminophosphine, Homogenous Catalysis, Transfer Hydrogenation, Rhodium.