Bidentate ligands are key components in many metal-mediated syntheses of organic molecules vital to pharmaceuticals and materials production; their chelate nature provides control and selectivity.
Related systems with two different donors (heteroditopic ligands) also give an asymmetric coordination environment that greatly alters a metals reactivity and catalytic behaviour. Continued ligand design remains crucial to the development of clean, efficient, sustainable manufacturing processes based on atom efficient metal-catalysed reactions.
A flexible synthetic strategy for the preparation of novel, bidentate phosphine-alkene ligands based on norbene skeletons (ALKENPHOS) will be developed, using simple P-N and -O bond-forming reactions. Two families of ligands will be prepared. A 7-aza-norbornene frame will provide rigid scaffolds offering an ideal metal binding pocket, while less rigid P-alkene ligands will be prepared from 2-hydroxy-norbene.
Both systems are a major departure from the types of heteroditopic ligands that have been prepared to date, presenting two very electronically and sterically different donor sites. This feature will provide control and unique reactivity for the resulting complexes by maximising the difference in Lewis basicity, pi-acidity and trans-influence between the two sites.
The easy synthesis of ALKENPHOS ligands allows for the easy introduction of chirality, important for their use in asymmetric catalysis. The readily available 1,1-binaphtholate-derived P-fragment is attractive since it is easily built-in and is very successful in asymmetric catalysis.
After quantification of their basicity/donor properties and preliminary coordination chemistry studies, the ALKENPHOS systems will be used in a range of homogeneous catalytic reactions that will exploit their novel composition and electronic character: alkene hydrogenation and the generally difficult to achieve but synthetically very attractive coupling of unactivated alkyl halides.
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