Synthesis and characterization of ferrocenyl-based C2 symmetric phosphinite ligands and their transition metal complexes and investigation of their catalytic activities in asymmetric transfer hydrogenation reactions

Asymmetric catalysis has become a growing field of study as the demand for more enantiomerically pure compounds arises. The design and synthesis of new chiral ligands for transition metals have played a significant role in the development of the asymmetric transfer hydrogenation reactions. Asymmetric catalysis requires that a chiral catalyst be used in order to transfer its chirality to the substrat. An effective asymmetric catalyst will quickly produce a chiral product in good yield with high enantiomeric purity of the desired enantiomer. In particular, asymmetric transfer hydrogenation of prochiral ketones to provide chiral alcohols has received a great deal of attention in the last decade or so. Compounds containing chiral metallocene ligands, in particular chiral ferrocenyl ligands, are one 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 group 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 chiral phosphines and aminophosphines form transition metal complexes which have already been identified as active catalysts in a variety of enantioselective reactions including hydrogenation, hydrosilylation, cross-coupling reactions and aldol condensation. Although some ferrocenyl aminoalcohols, phosphines, aminophosphines and iminodiphosphines have been employed successfully as ligands in ruthenium(II)-promoted transfer hydrogenation of ketones, a screening of catalytic activity of ferrocenyl phosphinites in this reaction is limited. In the present work, the ciral C2-symmetric ferrocenylaminoalcohols were prepared from the chiral compounds having different aril and alkyl groups, The new C2-symmetric bis phosphinite compounds were synthesized by the reaction of C2-symmetric ferrocenylaminoalcohols with Ph2PCl. Ru(II), Rh(I) and Ir(III) metal complexes of preparedphosphinite ligands were synthesized and characterized. Finally, use of these transition metal complexes as catalysts in asymmetric transfer hydrogenation reactions of aryl/alkyl and alkyl/alkyl ketones were investigated.