title: Molybdenum and Tungsten Imido Alkylidene N-Heterocyclic Carbene Catalysts Bearing Cationic Ligands for Use in Biphasic Olefin Metathesis.
abstract: Ionic Mo- and W-imido alkylidene N-heterocyclic carbene (NHC) olefin metathesis catalysts, [Mo{N-2,6-(Me2)C6H3}(CHCMe2Ph)(IMesH2)(OTf)(PPS)]OTf (3), [Mo(N-2,6-(Me2)C6H3)(CHCMe2Ph)(IMesH2)(OC6F5)(PPS)][B(ArF)4] (5), [Mo(NtBu)(CHCMe2Ph)(4,5-dichloro-1,3-dimethylimidazol-2-ylidene)(OTf)(2,6-Ph-4-{2,4,6-Ph-pyridinium}phenolate)][OTf] (9), [Mo(NtBu)(CHCMe2Ph)(4,5-dichloro-1,3-dimethylimidazol-2-ylidene)(2,6-Ph-4-{2,4,6-Ph-pyridinium}phenolate)][B(ArF)4]2(10, PPS=pyridiniumpropanesulfonate, IMesH2=1,3-dimesitylimidazolin-2-ylidene, OTf=CF3SO3, B(ArF)4=tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) were prepared from betaine-type ligands. Also, the first bis-NHC and a nitron-based bis(amido) bistriflate imido alkylidene complex, [Mo(NtBu)(CHCMe2Ph)(4,5-dichloro-1,3-dimethylimidazol-2-ylidene)2(THF)(2,6-Ph-4-{2,4,6-Ph-pyridinium}phenolate)][OTf]2(11) and [Mo(N-2,6-Me2-C6H3)(CHCMe2Ph)(N-{1,4-diphenyl-1,3,4-triazol-2-ylium}-N-phenyl-amido)2][OTf]2(14) along with ionic [W(N-2,6-iPr2-C6H3)(CHCMe2Ph)(N-2,5-Me2C4H2)(IiPr)(2,6-tBu-4-PPh3-phenolate)] (17, IiPr=1,3-diisopropylimidazol-2-ylidene) are reported. With these new catalysts, the first biphasic reaction setup with Group 6 metal alkylidene NHC complexes was successfully established using a pyrrole/heptane mixture as a liquid phase. Productivities under biphasic conditions were comparable to those of reactions in 1,2-dichloroethane or toluene. Metal concentrations of <2 ppm migrated into the nonpolar heptane phase as measured by inductively coupled plasma-optical emission spectroscopy.
authors.affiliation: Institute of Polymer Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
authors.forename: Iris
authors.initials: I
authors.lastname: Elser
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 Organic Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Frey
authors.affiliation: Institute of Polymer Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
authors.forename: Michael R
authors.identifier: http://orcid.org/0000-0001-6472-5156
authors.initials: MR
authors.lastname: Buchmeiser
keywords: betaines; biphasic catalysis; carbene ligands; metathesis; molybdenum