Synthesis, structure of iron(III)-containing imidazolium salts and their catalytic activity in the alkylation of aryl Grignard reagents

Abstract

A series of iron(III)-containing imidazolium salts of the general formula [DRim] [FeX 4 ] (R = 2,6-diisopropylphenyl, IPr, X = Cl, 1; R = IPr, X = Br, 2; R = tertbutyl, t Bu, X = Cl, 3; R = isopropyl, i Pr, X = Cl, 4; R = benzyl, Bn, X = Cl, 5; R = Bn, X = Br, 6) have been prepared in high yields via reactions of anhydrous ferric halides with equivalent of the corresponding N,N-dihydrocarby-limidazolium halides, where 2-6 are novel ones. All of the complexes were characterized by elemental analysis, Raman spectroscopy, electrospray ionization mass spectroscopy, and X-ray crystallography for 1 and 2. All of them were non-hygroscopic and air-stable, with four of them existing as solids (1-4) and two as liquids (5 and 6) at room temperature. A preliminary catalytic study on the coupling of 4-tolylmagnesium bromide with cyclohexyl bromide revealed that 1 and 3 possessed the highest activity. In comparison, 2, 4 and 5 exhibited moderate activity and the least active complex was 6. shown to be capability in this regard. Fe(acac) 3 (acac = acetylacetonate) are also active [10], although the addition of an amine additive was required to achieve a higher yield of the cross-coupled product [11]. Notably, an easily prepared iron(III)-containing imidazolium salt [bmim] [FeCl 4 ] (bmim = 1-butyl-3-methylimidazolium cation) can be used as a recyclable catalyst for the aryl Grignard cross-coupling of alkyl halides [12]. The use of imidazolium chloride can modify the highly hygroscopic FeCl 3 into an non-hygroscopic and air-stable complex, which provides a practical strategy for the design of iron(III)-based catalyst with potential large-scale applications [11].[bmim] [FeCl 4 ] has already been successfully used as a catalyst in other organic transformations, including the Friedel-Crafts sulfonylation of aromatics [13], a Biginelli condensation for the synthesis of dihydropyrimidinones [14], 2,5-norbornadiene dimerization [15], oxidative desulfurization of fuels [16], the glycolysis of poly(ethylene terephthalate) [17], and the regioselective benzylation of arenes and heteroarenes [18].

Iron Catalysis in Organic Synthesis

“…Six different iron(III)-containing imidazolium salts of the type shown in Figure have been synthesized and studied for the model transformation: a reaction of cyclohexyl bromide and p -tolylmagnesium bromide . While all iron-containing imidazolium salts gave high to excellent conversions, it could be shown that the efficiency of the catalyst can be adjusted by modification of the substituents at the imidazole ring.…”

Research on Iron-Containing Magnetic Ionic Liquids in Extraction-Deash of Coal Direct Liquefaction Residues Using Ultrasonic Oscillation

“…Synthesis of iron-containing magnetic ionic liquids. In this research, three kinds of iron-containing magnetic ionic liquids were synthesized, which were non-hygroscopic and air-stable [8]. They were [bmim]FeCl 4 , [bPy]FeCl 4 and [bmP]FeCl 4 .…”

Development of Fe(III)-containing ether-functionalized imidazolium ionic liquids for aryl Grignard cross-coupling of alkyl halides

“…In a continuation of our work focused on the development of Fe(III)-containing imidazolium ILs for use in the cross-coupling of aryl Grignard reagents with alkyl halides [9][10][11][12], we report here on the use of ether-functionalized imidazolium salts in the facile synthesis of a series of Fe(III)-containing ILs 1-6, and their use as catalysts in cross-coupling the aryl Grignard with alkyl halides with -hydrogens. Ether-functionalized imidazolium salts have demonstrated attractive physicochemical properties for particular applications, e.g.…”