Modelling and synthesis of alicyclic bidentate n– and o chelating ligands

Abstract

The well-defined ruthenium-carbene complexes reported by Grubbs and co-workers were the first ruthenium catalysts to show good activity and selectivity in metathesis of acyclic and cyclic olefins. Unfortunately the use of the Grubbs type catalysts is limited to the small scale synthesis of polymers and essential organic reactions, due to cost and instability of the catalyst at elevated temperatures. Some of the most successful Grubbs-type catalysts included hemilabile ligands. By releasing a free coordination site (the so-called "on-demand-open-site") for an incoming nucleophile, hemilabile ligands have the ability to increase the thermal stability and activity of a catalytic system, by stabilization of the transition metal centre. Previous studies indicated that the incorporation of a sterically hindered N and 0 chelating ligand increased the stability, activity and selectivity of Grubbs type complexes and increasing the electron density of the complex can influence the stability of a complex and therefore the catalytic performance. In this study alicyclic, bidentate N and 0 chelating ligands (16-19) were modelled in order to evaluate the hemilability of these ligands. The modelling was used as a comer stone from which the synthesis was conducted. Molecular modelling showed that of the four ligands identified only two (16 and 18) could potentially be hemilabile. 17 would rather form a transaunular ether compound. The modelling results were incondusive for ligand 19 and further investigation is necessary for this compound…