Balakrishna Bugga, PhD student under the supervision of Prof. Anton Vidal, has defended his PhD Thesis entitled ‘Development of P-OP Ligands with New Structural Motifs for Rhodium- and Iridium- Mediated Asymmetric Hydrogenations’ (assigned to the Organic and Analytical Chemistry Department of the Universitat Rovira i Virgili) publicly on September 9th at the ICIQ Library.
The members of the evaluation committee were: Prof. Asunción Barbero (Universidad de Valladolid), Prof. Antonio Frontera (Universitat de les Illes Balears) and Prof. Patrick Gámez (Universitat de Barcelona).
The thesis deals with design and synthesis of enantiopure phosphine-phosphite (P-OP) ligands with new phosphite fragments and coordination studies with rhodium and iridium precursors for asymmetric hydrogenations. The resulting P-OP-rhodium and iridium complexes were efficiently employed in asymmetric hydrogenations of an array of structurally diverse substrates. The synthetic rout of highest performing Rh(P-OP) precatalysts has been optimized by developing a chromatography-free synthesis involving the crystallization of the target [Rh(P-OP)] precatalysts as the purification method. Studies on [Ir(P-OP)]-mediated asymmetric hydrogenations of a variety of seven-membered heterocycles those contain C=N bonds have revealed that these iridium complexes are excellent catalysts (up to full conversion; up to 97% ee). The unexpected inversion in enantioselectivity has been rationalized by means of DFT calculations, which have identified the position of the Cl-ligand in catalytically relevant iridium structures and a number of non-covalent interactions (i.e. N-H···Cl, C-H···π and C-H···H-Ir interactions) as key features in the rationalization of the stereochemical outcome of the reactions. As regards to the hydrogenation of functionalized alkenes, [Rh(P-OP)] precatalysts incorporating new phosphite fragments have been prepared. High catalytic activity (>99% conversion) and excellent enantioselectivity (up to >99%) were achieved.