Synthesis of ferrocenyl-based chiral phosphinite ligands and Ru(II) complexes for reduction of aromatic ketones

Asymmetric catalysis has been a rapidly developing field to meet enantiomerically pure compounds. Obtaining chiral compounds as an enantiopure form is one of the most important aim of the modern organic chemistry. An efficient asymmetric catalyst affords a desired enantiomer in a high yield and in a short time. Use of chiral metal complexes as catalyst is considered as an economically applicable and powerful method to prepare optically active substances both in academic and industrially. A metal can exhibit an impelling enantioselectivity and activity when it coordinates to one or more chiral phosphorus ligands. Studies on developing efficient chiral phosphorus ligands, especially on those having chiral skeleton, are one of primary topics of asymmetric catalysis. The chemistry of phosphorus ligands such as, aminophosphines, phosphines, phosphites and phosphinites has also been intensively explored in recent years. These compounds are extremely attractive as potential ligands since various structural modifications are accessible via simple P-N, P-C and P-O bond formation. Many modified phosphine ligands and a variety of chiral phosphinite ligands have important applications in organometallic chemistry and catalysis, giving selective catalysts for hydroformylation, hydrosilylation and asymmetric transfer hydrogenation Compounds containing chiral metallocene ligands, in particular chiral ferrocenyl ligands, constitute an important class of asymmetric catalysts that has received significant attention in recent years due to the versatility of these catalysts in a variety of applications. The ferrocenyl moiety has been widely explored in different areas, from polymers to bioorganometallic chemistry. Among several applications, the use of ferrocene-based chiral ligands in asymmetric synthesis is the most prominent. Ferrocene-based aminophosphine ligands have been shown to be effective in the ruthenium(II)-catalysed asymmetric transfer hydrogenation of ketones. The enantioselectivity is mainly determined by the carbon centred chirality of the ligands, but the planar chirality is also important. Ferrocenyl iminodiphosphine ligands are also effective for the asymmetric transfer hydrogenation of methyl aryl ketones. Although some ferrocenyl aminoalcohols, aminophosphines and phosphines have been employed successfully as ligands in Ru(II)-promoted transfer hydrogenation of ketones, a screening of catalytic activity of ferrocenyl based phosphinites in this reaction has not yet reported so much. In the present work, the chiral ferrocenyl compounds prepared from chiral compounds having different R groups; the new phosphinite compounds were synthesized by the reaction of the chiral ferrocenyl aminoalcohols with Ph2PCl, and characterized. Finally, use of the Ru(II) complexes as catalysts in asymmetric transfer hydrogenation reactions of ketones investigated.