Molybdenum Imido Alkylidene N‐Heterocyclic Carbene Complexes: Structure–Productivity Correlations and Mechanistic Insights

Abstract

Abstract 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 ‐C 6 H 3 )((1‐ R ‐phenethyl)‐3‐mesitylimidazolidin‐2‐ylidene)(CHR)(OTf) 2 (R=CMe 2 Ph, 1 ) is the first enantiomerically pure Mo–imido alkylidene NHC catalyst. With [Mo( N ‐2,6‐Me 2 ‐C 6 H 3 )(IMes)(CHR)(CH 3 CN)(OTf)(CH 3 CN) + 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 (TOF 4 min ) of 8860 min −1 was determined. Productivity and E / Z ‐selectivity were correlated with catalyst structure. For 1 , Mo( N ‐3,5‐Me 2 ‐C 6 H 3 )(IMesH 2 )(CHR)(OTf) 2 ( 9 ) and Mo( N ‐3,5‐Me 2 ‐C 6 H 3 )(IMes)(CHR)(OTf) 2 ( 10 ), productivity was correlated with the coalescence temperature of the two triflates, determined by variable‐temperature 19 F NMR spectroscopy. The square‐planar conformer is postulated to be the most relevant for the catalyst activation.