Preparation Of Novel Tetraphosphonite And P/N Heterobidenate Ligand

Since the discovery of BINAP by Noyori in 1980's, this ligand successfully applied in a variety asymmetric hydrogenetation, and several large scale asymmetric syntheses are now carried out with BINAP. The development of tetraphosphine ligands and the bimetallic coorperativity have been summarized in this thesis. Tetraphosphine ligand(eLTTP) desinged by Stanley can simultaneously bridge and chelate two metal centers to create bimetallic complexes with considerable conformational flexibility. The racemic bimetallic Rh complex is an excellent hydroformylation catalyst for 1-alkenes ,giving both a high rate of reaction and high regioselectivity for linear aldehydes. Elightened by eLTTP, we hope to prepare a series of tetraphosphonite of linked-BINOL frame, which combine atropisomery and conformational flexibility.An enormous variety of chiral phosphine ligands has been developed, many of these ligands enduce very high enantioselectivity in rhodium and ruthenium-catalyzed hydrogenations. But both of them require the presence of a polar functional group next to the C=C bond, which can coordinate to the metal center. With unfunctionalized olefins, these catalysts generally show low reactivity and unsatisfactory enantioselectivity. Some years ago, some iridium complexes with chiral P, N ligands that overcome these limitations. Various unfunctionalized aryl-substituted olefins can be hydrogenated with high enantioselectivity and high catalytic efficiency using this type of catalysts. In asymmetric catalysis ligands the asymmetry induced by ligands in a reaction, is caused not just through the steric factors, but also by the electronic asymmetry on the metal centre from the presence of different donor atoms. Theπ-acceptor character of the phosphorus can stabilise a metal centre in a low oxidation state, while 6 -donor ability of nitrogen makes the metal be more susceptible to oxidative addition reactions. This combination can help to stabilise intermediate oxidation states or geometries which form during a catalytic cycle. We synthesized a series of Schiff base from an intermediate prepared in the tetraphosphonite section and different substituted amines, and then turn them to P/N heterobidenate ligands.