Teng, Q. Q.; Wu, W. Q.; Duong, H. A.; Huynh, H. V., Ring-expanded N-heterocyclic carbenes as ligands in iron-catalysed cross-coupling reactions of arylmagnesium reagents and aryl chlorides Chemical Communications 2018, 54 (47), 6044-6047.
The structure–activity relationship of expanded-ring N-heterocyclic carbenes (NHCs) in the iron-catalysed Kumada aryl–aryl coupling reaction was explored. This was achieved by comparing the catalytic performance of Fe-NHC catalysts generated in situ containing NHCs that differ in steric bulk. In particular, the influences of ring sizes (5–8) and N-aryl substituents were explored in terms of spectroscopic and structural features, which affect their %Vbur values. The three best performing ligands were found on a diagonal of a 5 × 4 structural matrix revealing an optimal steric bulk and significant influences of subtle steric variations on the catalytic activities.
This work was funded by ‘‘GSKEDB Singapore Partnership for Green and Sustainable Manufacturing’’, the Institute of Chemical and Engineering Sciences (ICES), Agency for Science, Technology and Research (A*STAR), Singapore and the National University of Singapore (NUS, WBS R143000580592).