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The Pivotal Role of Symmetry in the Ruthenium‐Catalyzed Ring‐Closing Metathesis of Olefins
Author(s) -
Costabile Chiara,
Mariconda Annaluisa,
Cavallo Luigi,
Longo Pasquale,
Bertolasi Valerio,
Ragone Francesco,
Grisi Fabia
Publication year - 2011
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201100483
Subject(s) - carbene , catalysis , chemistry , ruthenium , ring closing metathesis , steric effects , phosphine , metathesis , aryl , olefin metathesis , ring (chemistry) , catalytic cycle , salt metathesis reaction , medicinal chemistry , combinatorial chemistry , stereochemistry , organic chemistry , alkyl , polymerization , polymer
The synthesis of Ru‐based precatalysts with N‐heterocyclic carbene (NHC) ligands bearing syn‐ and anti ‐methyl groups on the NHC backbone and aryl N‐substituents with differing steric bulk was carried out. The catalytic behavior of the monophospine Ru precatalysts ( 7 a , 7 b, 8 a , and 8 b ) was compared to the corresponding family of phosphine‐free catalysts ( 9 a, 9 b, 10 a and 10 b ) in the ring‐closing metathesis (RCM) of olefins. These catalysts showed high efficiency in RCM reactions and the syn ‐isomers 7 a and 9 a , in particular, proved to be among the most active catalysts in the formation of tetrasubstituted olefins through RCM. DFT studies on the entire RCM catalytic cycle of hindered olefins were performed to rationalize the different behaviors of catalysts with syn‐ and anti ‐methyl groups on the NHC backbone. Theoretical results not only disclosed how NHC symmetry influences the overall activity of the catalyst, but also gave relevant and more general indications on the crucial steps of the RCM of olefins.