Molybdenum Imido Alkylidene N-Heterocyclic Carbene Complexes: Structure-Productivity Correlations And Mechanistic Insights (Vol 8, Pg 2710, 2016)

The syntheses and single-crystal X-ray structures of a series of Mo-imido alkylidene N-heterocyclic carbene (NHC) complexes (1-15) and of the first complexes containing bidentate NHC-phenolate ligands (16-18) are reported. Mo(N-2,6-Me-2-C6H3)((1-R-phenethyl)-3-mesitylimidazolidin-2-ylidene)(CHR)(OTf) 2 (R=CMe2Ph, 1) is the first enantiomerically pure Mo-imido alkylidene NHC catalyst. With [Mo(N-2,6-Me-2-C6H3)(IMes)(CHR)(CH3CN)(OTf)(CH3CN)(+) B(Ar-F)(4)(-)] (7), turnover numbers up to 545 000 were achieved in the homometathesis (HM) of 1-octene and 1-nonene (<95% E). With 7 and 1-nonene, a turnover frequency (TOF4min) of 8860 min(-1) was determined. Productivity and E/Z-selectivity were correlated with catalyst structure. For 1, Mo(N-3,5-Me-2-C6H3)(IMesH(2))(CHR)(OTf) 2 (9) and Mo(N-3,5-Me-2-C6H3)(IMes)(CHR)(OTf)(2) (10), productivity was correlated with the coalescence temperature of the two triflates, determined by variable-temperature F-19 NMR spectroscopy. The square-planar conformer is postulated to be the most relevant for the catalyst activation.