The synthesis of Ru-based precatalysts with N-heterocyclic car- bene (NHC) ligands bearing syn- and anti-methyl groups on the NHC back- bone and aryl N-substituents with dif- fering steric bulk was carried out. The catalytic behavior of the monophospine Ru precatalysts (7a, 7b, 8a, and 8b) was compared to the corresponding family of phosphine-free catalysts (9a, 9b, 10a and 10b) in the ring-closing metathesis (RCM) of olefins. These catalysts showed high efficiency in RCM reactions and the syn-isomers 7a and 9a, 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 in- fluences the overall activity of the cata- lyst, but also gave relevant and more general indications on the crucial steps of the RCM of olefins.
The Pivotal Role of Symmetry in the Ruthenium-Catalyzed Ring-Closing Metathesis of Olefins
BERTOLASI, Valerio;
2011
Abstract
The synthesis of Ru-based precatalysts with N-heterocyclic car- bene (NHC) ligands bearing syn- and anti-methyl groups on the NHC back- bone and aryl N-substituents with dif- fering steric bulk was carried out. The catalytic behavior of the monophospine Ru precatalysts (7a, 7b, 8a, and 8b) was compared to the corresponding family of phosphine-free catalysts (9a, 9b, 10a and 10b) in the ring-closing metathesis (RCM) of olefins. These catalysts showed high efficiency in RCM reactions and the syn-isomers 7a and 9a, 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 in- fluences the overall activity of the cata- lyst, but also gave relevant and more general indications on the crucial steps of the RCM of olefins.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
