Salen coordination compounds as Lewis acid catalysts
thesisposted on 15.12.2014, 10:35 by Pedro R. Villuendas
In this research a range of salen ligands have been synthesised with a variety of diamine backbones.;Derivatives of these ligands (M = Ni(II), Zn(II), Cu(II)) have subsequently been prepared and used as catalysts in the synthesis of enaminodiones, the enantioselective alkylation of carbonyls and imines, the enantioselective trifuoromethylation and the enantioselective Reformatsky reaction.;Yields better than 90% were achieved for the enaminodiones reaction for [Zn(salen)] derivatives in 24 hours and a range of substrates was studied. Once the best catalysts and conditions were determined, experiments were carried out in order to determine the recyclability of the catalyst by supporting it on Silica gel or FRPSG (Fluorous Reverse Phase Silica Gel). Unfortunately, only one catalyst could be recovered four times without loosing activity. ICP/MS showed large amounts of Zn in the organic phase.;In the enantioselective addition of ZnEt2 to benzaldehyde, the conversion was calculated by 1H NMR spectroscopy and the enantioselectivity was calculated using chiral GC. Non fluorous [Zn(Salen)] demonstrated to enhance enatioselectivity better than fluorous ones. However, results for one fluorous salen ligand were good enough to perform recycling experiments using FPSE (Fluorous Solid Phase Extraction).;In the enantioselective trifluoromethylation of benzaldehyde the conversions were calculated by 1H NMR spectroscopy and enantioselectivities were studied by chiral GC. Poor enantioselectivities were obtained and [M(salen)] complexes demonstrated not to be catalysts for this reaction. In the enantioselective Reformatsky reaction the conversion were calculated by 1H NMR spectroscopy and the enantioselectivity was calculated by using a chiral solvent. However, no enantioselectivity was induced in any case. In the enantioselective addition of ZnEt2 to benzaldehyde the conversion was calculated by 1H NMR spectroscopy and the enantioselectivity was calculated by HPLC. No enantioselectivity was induced using these catalysts.