title: Neutral and Cationic Molybdenum Imido Alkylidene N-Heterocyclic Carbene Complexes: Reactivity in Selected Olefin Metathesis Reactions and Immobilization on Silica.
abstract: The synthesis and single-crystal X-ray structures of the novel molybdenum imido alkylidene N-heterocyclic carbene complexes [Mo(N-2,6-Me2C6H3)(IMesH2)(CHCMe2Ph)(OTf)2] (3), [Mo(N-2,6-Me2C6H3)(IMes)(CHCMe2Ph)(OTf)2] (4), [Mo(N-2,6-Me2C6H3)(IMesH2)(CHCMe2Ph)(OTf){OCH(CF3)2}] (5), [Mo(N-2,6-Me2C6H3)(CH3CN)(IMesH2)(CHCMe2Ph)(OTf)](+)BArF(-) (6), [Mo(N-2,6-Cl2C6H3)(IMesH2)(CHCMe3)(OTf)2] (7) and [Mo(N-2,6-Cl2C6H3)(IMes)(CHCMe3)(OTf)2] (8) are reported (IMesH2=1,3-dimesitylimidazolidin-2-ylidene, IMes=1,3-dimesitylimidazolin-2-ylidene, BArF(-)=tetrakis-[3,5-bis(trifluoromethyl)phenyl] borate, OTf=CF3SO3(-)). Also, silica-immobilized versions I1 and I2 were prepared. Catalysts 3-8, I1 and I2 were used in homo-, cross-, and ring-closing metathesis (RCM) reactions and in the cyclopolymerization of α,ω-diynes. In the RCM of α,ω-dienes, in the homometathesis of 1-alkenes, and in the ethenolysis of cyclooctene, turnover numbers (TONs) up to 100,000, 210,000 and 30,000, respectively, were achieved. With I1 and I2, virtually Mo-free products were obtained (<3 ppm Mo). With 1,6-hepta- and 1,7-octadiynes, catalysts 3, 4, and 5 allowed for the regioselective cyclopolymerization of 4,4-bis(ethoxycarbonyl)-1,6-heptadiyne, 4,4-bis(hydroxymethyl)-1,6-heptadiyne, 4,4-bis[(3,5-diethoxybenzoyloxy)methyl]-1,6-heptadiyne, 4,4,5,5-tetrakis(ethoxycarbonyl)-1,7-octadiyne, and 1,6-heptadiyne-4-carboxylic acid, underlining the high functional-group tolerance of these novel Group 6 metal alkylidenes.
authors.affiliation: Institute of Polymer Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart (Germany).
authors.forename: Suman
authors.initials: S
authors.lastname: Sen
authors.affiliation: Institute of Polymer Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart (Germany).
authors.forename: Roman
authors.initials: R
authors.lastname: Schowner
authors.affiliation: Institute of Polymer Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart (Germany).
authors.forename: Dominik A
authors.initials: DA
authors.lastname: Imbrich
authors.affiliation: Institute of Organic Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart (Germany).
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Frey
authors.affiliation: Institute of Chemical Technology, University of Stuttgart, Pfaffenwaldring 55, 70569 (Germany).
authors.forename: Michael
authors.initials: M
authors.lastname: Hunger
authors.affiliation: Institute of Polymer Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart (Germany). michael.buchmeiser@ipoc.uni-stuttgart.de.|Institute of Textile Chemistry and Chemical Fibers, Körschtalstr. 26, 73770 Denkendorf (Germany). michael.buchmeiser@ipoc.uni-stuttgart.de.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Buchmeiser
keywords: N-heterocyclic carbenes; alkylidene; immobilization; molybdenum; olefin metathesis