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.
Abstract:
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.
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Funding Info:
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).