Silica‐Supported Molybdenum Alkylidyne N‐Heterocyclic Carbene Catalysts: Relevance of Site Isolation to Catalytic Performance

Abstract

AbstractThe immobilization of the molybdenum alkylidyne complex [(p‐OMe‐C6H4C≡)Mo(OCMe(CF3)2)3⋅DME] (DME=1,2‐dimethoxyethane) on silica using a silica‐supported N‐heterocyclic carbene (NHC), that is, 1,3‐di(isopropyl)imidazol‐2‐ylidene, is reported. Two different types of silica, that is, silica 60 and partially dehydroxylated silica 60 obtained via heating to 650 °C (SiO2‐650) were used. In both cases, excess silanol groups were end‐capped with trimethylsilyl chloride. Immobilization of both the NHC precursor and the metal alkylidyne was followed by 19F magic angle spinning (MAS) and 13C cross‐polarization magic angle spinning (CPMAS) NMR and inductively‐coupled optical emission spectroscopy (ICP–OES). The metal alkylidyne supported on both types of silica was active in alkyne metathesis and showed activity for a series of functional 2‐alkynes. Most importantly, the metal alkylidyne supported on SiO2‐650 displayed a substantially higher alkyne metathesis activity than the homogeneous analog or the one supported on regular silica, which is attributed to a site isolation effect and, as a result, reduced bimolecular decomposition.