Molybdenum and Tungsten Imido Alkylidene N-Heterocyclic Carbene Catalysts Bearing Cationic Ligands for Use in Biphasic Olefin Metathesis.

Ionic Mo- and W-imido alkylidene N-heterocyclic carbene (NHC) olefin metathesis catalysts, [Mo{N-2,6-(Me2 )C6 H3 }(CHCMe2 Ph)(IMesH2 )(OTf)(PPS)]OTf (3), [Mo(N-2,6-(Me2 )C6 H3 )(CHCMe2 Ph)(IMesH2 )(OC6 F5 )(PPS)][B(ArF )4 ] (5), [Mo(NtBu)(CHCMe2 Ph)(4,5-dichloro-1,3-dimethylimidazol-2-ylidene)(OTf)(2,6-Ph-4-{2,4,6-Ph-pyridinium}phenolate)][OTf] (9), [Mo(NtBu)(CHCMe2 Ph)(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=CF3 SO3 , 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)(CHCMe2 Ph)(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 -C6 H3 )(CHCMe2 Ph)(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 -C6 H3 )(CHCMe2 Ph)(N-2,5-Me2 C4 H2 )(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.