title: The pivotal role of symmetry in the ruthenium-catalyzed ring-closing metathesis of olefins.
abstract: 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 (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 influences the overall activity of the catalyst, but also gave relevant and more general indications on the crucial steps of the RCM of olefins.
authors.affiliation: Dipartimento di Chimica e Biologia, Università degli Studi di Salerno, Via Ponte Don Melillo, 84084 Fisciano, Salerno, Italy.
authors.forename: Chiara
authors.initials: C
authors.lastname: Costabile
authors.forename: Annaluisa
authors.initials: A
authors.lastname: Mariconda
authors.forename: Luigi
authors.initials: L
authors.lastname: Cavallo
authors.forename: Pasquale
authors.initials: P
authors.lastname: Longo
authors.forename: Valerio
authors.initials: V
authors.lastname: Bertolasi
authors.forename: Francesco
authors.initials: F
authors.lastname: Ragone
authors.forename: Fabia
authors.initials: F
authors.lastname: Grisi