Synthesis and characterisation of MOP-phosphonite complexes and their applications in asymmetric catalysis

Abstract

In this thesis we report our synthesis of user-friendly, chiral phosphonite ligands, based upon Hayashi’s MOP backbone, and their application in asymmetric catalytic transformations. Chapter 1 gives an introduction to organophosphorus ligands in catalysis and the use of air-stable primary phosphines as precursors in the synthesis of functionalised phosphorus compounds. Chapter 2 details our synthesis and characterisation of the enantiopure MOP-phosphonite ligands (S)-28a and (R)-28b containing two phenoxy substituents, (S)-29a and (R)-29b with a biphenoxy moiety and (S)-30a and (R)-30b with a 3,3'-dimethylbiphenoxy group. These ligands are proven to be very successful in high-yielding, regio- and enantioselective palladium-catalysed hydrosilylation reactions of substituted styrenes, affording important chiral secondary alcohols, with (S)-30a achieving ees of up to 95%. In-depth NMR studies reveal the hemilabile nature of the bonding of (R)-30a in a palladium 2-methylallyl complex, where the phosphonite ligand acts as a chelating P,C-π-donor. In Chapter 3 we compare our series of novel ligands via experimental and computational methods in an effort to quantify their differing structural and electronic profiles. Four [Rh(LP)(η2:η2-cod)Cl] and two [Rh(LP)2]BF4 complexes were synthesised and characterised by NMR spectroscopy, HRMS and, in all but one case, by X-ray crystallography. Rh() complexes were used as catalysts in industrially relevant asymmetric hydrogenation and hydroformylation reactions. Pd() complexes were successfully employed in asymmetric Suzuki-Miyaura cross-coupling reactions yielding binaphthyl products and two of the [Pd(LP)2Cl2] catalysts were isolated and characterised by X-ray crystallography. The final chapter details the preparation of copper, silver and gold complexes of our MOP-phosphonites. Six [Au(LP)Cl] complexes were prepared as was the complex [Au((S)-30a)2]SbF6. Six [Ag(LP)OTf] complexes were synthesised, as were six [Cu(LP)(MeCN)2]PF6 complexes. Extensive NMR and X-ray crystallographic analyses undertaken on these compounds reveals that any M–π interactions appear weak, if present at all.