Dr Nancy Dervisi - PhD
3.3.0 bicyclic ligand frameworks
An area currently pursued in the group is the study of phosphine ligands based on 3.3.0 bicyclic frameworks. This project fits with our broader interest in the design of more rigid, sterically controlled chiral ligands derived from the hydrocarbon chiral pool (sugars in particular). Such ligands offer the advantages of predetermined backbone chirality with often rigid structure and high degree of peripheral functionalisation. Chelating diphosphine ligands derived from D-isomannide 1, a mannitol dehydration product, and their TM complexes 2 have been isolated. In this case, we have taken advantage of the predetermined backbone chirality of a naturally occurring polyol (mannitol) and prepared chelating diphosphines with 4 chiral centres in only two steps. Presently, we are in the process of preparing NHC (N-heterocyclic carbene) precursors 3 based on the isomannide framework.
Large ring N-heterocyclic Carbene Ligands
The strong s-donating properties of NHCs make them effective stabilizing ligands in organometallic chemistry as well as important ligands in some forms of catalysis. To date research has largely focused on five-membered ring carbenes. Previously, we reported the first examples of novel, saturated, seven-membered diazepanylidene carbenes and their transition metal complexes, in collaboration with Fallis & Cavell.
A simple, versatile and high yielding route from amidines was also devised, leading to 6- and 7- membered carbenes (and saturated 5-membered NHCs). This methodology allows the isolation of a range of carbenes, and hence metal complexes, which are not available via other routes.
Six-, and in particular, seven-membered ring carbenes are intriguing from several points of view. They are very basic, somewhat more basic than the saturated 5-membered-ring carbenes, which are in turn more basic than their unsaturated counterparts. Structurally they also offer some unique features. The saturated seven-membered ring is highly twisted providing an opportunity to design new chiral ligand systems and the large heterocyclic rings lead to large N-CNHC-N angles.
Hybrid P,S ligand systems
In this area we are involved in the synthesis and catalytic applications of hybrid P,S ligands; studying the effect of bulky substituents on the P,S backbone in relation to co-ordination and catalysis. Previously, we have reported their applications in palladium-catalysed C-C coupling reactions. Some of these catalysts desirable features are: air and water stability, high tofs’ and catalyst recyclability. Their water stability has enabled us to develop a biphasic Heck system where simple inorganic bases such as NaOH are used instead of organic bases.