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

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-dihydro- carby-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.