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Silica‐Supported Molybdenum Alkylidyne N‐Heterocyclic Carbene Catalysts: Relevance of Site Isolation to Catalytic Performance
Author(s) -
Hauser Philipp M.,
Hunger Michael,
Buchmeiser Michael R.
Publication year - 2018
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201701654
Subject(s) - carbene , chemistry , silanol , carbyne , metathesis , alkyne , catalysis , magic angle spinning , molybdenum , salt metathesis reaction , polymer chemistry , nuclear magnetic resonance spectroscopy , organic chemistry , polymerization , polymer
The immobilization of the molybdenum alkylidyne complex [( p ‐OMe‐C 6 H 4 C≡)Mo(OCMe(CF 3 ) 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 (SiO 2‐650 ) 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 19 F magic angle spinning (MAS) and 13 C 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 SiO 2‐650 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.