- Heterogenization of Pd-NHC complexes onto a silica support and their application in Suzuki-Miyaura coupling under batch and continuous flow conditions
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The heterogenisation of a new family of Pd-NHC complexes is reported via a straightforward and efficient synthetic procedure. These silica-immobilised materials were successfully applied as catalysts in the Suzuki-Miyaura coupling of aryl chlorides and bromides under mild conditions. The materials exhibited improved stability when the catalytic reaction was run under anhydrous conditions and could be recycled up to five times without significant loss of activity. When the reaction was run within a continuous flow microreactor, these catalysts showed good activity after at least two hours on stream.
- Martnez, Alberto,Krinsky, Jamin L.,Peafiel, Itziar,Castilln, Sergio,Loponov, Konstantin,Lapkin, Alexei,Godard, Cyril,Claver, Carmen
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- Modular synthesis of functionalisable alkoxy-tethered N-heterocyclic carbene ligands and an active catalyst for buchwald-hartwig aminations
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Modular syntheses of functionalised, alkoxy-tethered 1,3-bis(2,4,6- trimethylphenyl)imidazolium (IMes*H+) and 1,3-bis(2,6- diisopropylphen-l)imidazolium (IPr*H+) derivatives 1,3-bis(4-alkyl- -2,4,6-trimethylphenyl)imidazolium (IXyOR*H+) and 1,3-bis(4-alkyl-oxy-2,6-diisopropylphenyl)imidazolium (IPrOR*H +) are reported. A reliable synthesis of the key starting material 4-amino-3,5-diisopropylphenol is also described. Etherification of hydroxydecorated ligand intermediates before formation of the imidazolium core and subsequent modification, or direct etherification of the versatile synthon IPrOH·HCl, allowed access to various linker types including triethoxysilyl, primary amino and norbornenyl, which are not accessible by other methods. An IPrOR-palladium(II) complex was prepared, and its catalytic activity was evaluated in challenging Buchwald- Hartwig aminations of aryl chlorides. This precatalyst displayed excellent activity and selectivity under mild reaction conditions, achieving in some cases a 10-fold improvement in TOF relative to the IPr-based version. An unexpected activity profile was observed wherein sterically demanding anilines were coupled more easily than those lacking orthosubstitution.
- Krinsky, Jamin L.,Martinez, Alberto,Godard, Cyril,Castillon, Sergio,Claver, Carmen
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p. 460 - 474
(2014/05/20)
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