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Synthesis and Characterization of Pyrazolyl‐Functionalized Imidazolium‐Based Ionic Liquids and Hemilabile (Carbene)palladium(II) Complex Catalyzed Heck Reaction
Author(s) -
Wang Ruihu,
Zeng Zhuo,
Twamley Brendan,
Piekarski Melissa M.,
Shreeve Jean'ne M.
Publication year - 2007
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200600828
Subject(s) - chemistry , carbene , catalysis , palladium , amide , alkyl , ionic liquid , heck reaction , medicinal chemistry , reagent , polymer chemistry , organic chemistry
Neat reactions of 1‐(pyrazolylmethyl)imidazole with an excess of alkyl or polyfluoroalkyl halides at 100 °C followed by subsequent metathetical reactions with LiN(SO 2 CF 3 ) 2 or KPF 6 at 25 °C gave rise to a series of monoquaternary salts 3a – 3k . These salts can be also prepared through treatment of 1‐alkylimidazole with 1‐(chloromethyl)pyrazole hydrochloride in the presence of base, followed by anion exchange with LiN(SO 2 CF 3 ) 2 or KPF 6 . Their phase‐transition temperature, thermal stability, density and solubility in common solvents have been investigated. Most of the bis(trifluoromethanesulfon)amide salts are room‐temperature ionic liquids. The effect of anions and of alkyl substituents bonded to the imidazolium cation on the physicochemical properties was examined. Using 3‐butyl‐1‐(pyrazolylmethyl)imidazolium chloride ( 2d ), the precursor of 3‐butyl‐1‐(pyrazolylmethyl)imidazolium bis(trifluoromethanesulfon)amide ( 3d ), as a reactant, a hemilabile (N‐heterocyclic carbene)palladium(II) complex 4 was synthesized through a (carbene)silver(I) transfer reagent. It was characterized by single‐crystal X‐ray diffraction analysis. The catalytic activity and recyclability of 4 in 3d were preliminarily evaluated by consecutive Heck reactions using different substrates. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)