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-(Me )C H }(CHCMe Ph)(IMesH )(OTf)(PPS)]OTf (3), [Mo(N-2,6-(Me )C H )(CHCMe Ph)(IMesH )(OC F )(PPS)][B(Ar ) ] (5), [Mo(NtBu)(CHCMe Ph)(4,5-dichloro-1,3-dimethylimidazol-2-ylidene)(OTf)(2,6-Ph-4-{2,4,6-Ph-pyridinium}phenolate)][OTf] (9), [Mo(NtBu)(CHCMe Ph)(4,5-dichloro-1,3-dimethylimidazol-2-ylidene)(2,6-Ph-4-{2,4,6-Ph-pyridinium}phenolate)][B(Ar ) ] (10, PPS=pyridiniumpropanesulfonate, IMesH =1,3-dimesitylimidazolin-2-ylidene, OTf=CF SO , B(Ar ) =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)(CHCMe Ph)(4,5-dichloro-1,3-dimethylimidazol-2-ylidene) (THF)(2,6-Ph-4-{2,4,6-Ph-pyridinium}phenolate)][OTf] (11) and [Mo(N-2,6-Me -C H )(CHCMe Ph)(N-{1,4-diphenyl-1,3,4-triazol-2-ylium}-N-phenyl-amido) ][OTf] (14) along with ionic [W(N-2,6-iPr -C H )(CHCMe Ph)(N-2,5-Me C H )(IiPr)(2,6-tBu-4-PPh -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.