Research objectives and content
Recently the Osborn group has shown that the Rh(l) and Ir(l) complexes of tridentate ligands of a particular structure are surprisingly active in hydrogenation of unsaturated C=C, C=O, and C=N bonds and that the chiral analogues of C 2 symmetry give good enantioselectivities in such reactions.
We propose develope the use of both achiral and chiral ligands to study the following catalytic reactions:
1 Study the complexes of tridentate ligands with Ru(ll) and their resultant cataytic properties. Such complexes may find particular application in the asymmetric hydrogenation of ketones. Although catalyst systems are known to yield high enantioselectivities in the reduction of appropriately functionalised ketones the conditions of the reduction still requires high hydrogen pressures to be affective. Our work would aim to improve on this situation since a) the tridentate ligands permit the creation of the chiral pocket about the incoming substrate - and a greater shape recognition for unfunctionalised substrates, b) electron rich ligands such should show increased activity and c) our synthetic approach can easily be extended to other beckbone structures. 2 Catalysed allylation reactions have been very well studied and elaborate bidentate ligands developed by Trost to obtain high
enantioselectivities. The use of tridentate ligands will introduce two interesting effects. Firstly, the Pd/allyl cationic intermediate will undoubtedly be the monohapto (a) form. The Osborn Group has shown with achiral tridentate analogues that nucleophilic attack and the overall catalysis are both more rapid than in known Pd systems with bidentate ligands. We will extend these studies to the chiral C2 tridentate ligand systems. Secondly the chiral pocket generated by some tridentate ligands can interact better with the external nucleophile and achieve a more generally applicable catalyst than is knows at present.
3 As mentioned above we intend to use our synthetic strategy of attaching ligands functions to rigid backbones for the elaboration of other tridentate ligands such as derivatives of xanthenes and the like. Training content (objective, benefit and expected impact)
The applicant will learn synthetic methodology (often under anaerobic conditions-globe box and vacuum line use) in both organic (ligand synthesis) and organometallic chemistry. The use of modern spectroscopic methods (particularly multinuclear NMR and MS) will also be involved. Training in the methods and scientific approaches of research in homogeneous catalysis will be especially useful for the future career of the applicant.
Links with industry / industrial relevance (22)
Although the laboratory has close contacs with industry (mainly Rhone-Poulenc and Ciba-Geigy) this project has no funding as yet from-industrial sources. However from 1987 to 1993 the laboratory has collaborated with Ciba-Geigy on the Ir(I) catalysed asymmetric hydrogenation of imines which has recently started up commercially which has therefore led to the understanding of industrial methods and criteria.