DESIGN, SYNTHESIS AND APPLICATION OF NEW MONO- AND MULTI-DENTATE CHIRAL LIGANDS WITH DONOR PHOSPHOROUS FOR ASYMMETRIC HOMOGENEOUS CATALYSIS

The first member of a new non conventional class of phosphepines, the class of the heterobinepines, has been synthesized: the tetraMe bithieno-dihydro-phosphepine. The new ligand has been resolved into antipodes and fully characterized structurally and chiroptically. The dihedral angle between the two interconnected thiophene rings is one of the narrowest known for hindered biaromatic systems. A detailed electrochemical investigation has been performed in order to evaluate the electronic availability at the phosphorous atom of the new ligand, in comparison with other phosphepines characterized by carbocyclic atropisomeric scaffolds, like Biphenine, Binepine and DiMeO-Biphenine. The bithienophosphepine was recognized as a rather electron-poor phosphane. The reactivity and the enantioselection ability shown by the metal complexes of the new phosphane were compared with those exhibited by structurally related ligands, like Ph-Binepine. In particular the rhodium catalysed asymmetric hydrogenation of N-acyl-enaminoacids, the palladium catalysed asymmetric allylic alkylation of 1,3-diphenylpropenyl acetate and the platinum catalysed asymmetric hydroxycyclization of 1,6 enynes have been investigated. Only in the latter reaction fast rates and high enantiomeric excesses could be achieved. The synthetic accesses to an analogous biindolophosphepine and to a [2.2]paracyclophane monodentate phosphane have been investigated. The first chiral D2 symmetric tetraphosphane was synthesized: the [2.2]paracyclophane tetra-diphenylphosphane. The new ligand was resolved into antipodes at the level of the corresponding oxide and fully characterized from the structural and chiroptical point of view. The reactivity and the enantioselection ability shown by the metal complexes of the tetraphosphane have been compared with those exhibited by the structurally related ligand Phanephos. In particular the rhodium complexes of the two ligands have been compared in asymmetric hydrogenation reactions of carbon-carbon double bonds of several N-acyl-enaminoacids as substrates. The [2.2]paracyclophane-tetraphosphane has been employed to investigate the formation of rhodium and palladium complexes, demonstrating the feasibility of heterobimetallic complexes. The synthetic accesses to a bithiophene-based tetraphosphane has also been investigated. In collaboration with the research group of dr. Andrea Penoni of Università degli Studi dell’Insubria in Como, new protocols for the enantioselective PKRs have been studied. The ligands BINAP, tetraMe-BITIOP and BITIANP have been tested in conventional cobalt and rhodium catalysed asymmetric PKR and in non-conventional rhodium catalysed asymmetric PKR whit an aldehyde as CO supplier.