Cu(i)/(ii) based catalytic ionic liquids, their metallo-laminate solid state structures and catalytic activities in oxidative methanol carbonylation

Abstract

Three types of copper-containing catalytic ionic liquids (CILs) have been synthesised and fully characterised by spectroscopy, elemental, thermal and, in most cases, XRD analyses. Whereas type I ILs comprise copper exclusively in the cation (e.g. [Cu(Im12)4][PF6], Im12 = 1-dodecylimidazole), type II ionic liquids contain Cu(I) in both the cation and the anion (e.g. [Cu(Im12)2][CuBr2]) and type III ILs incorporate copper solely in form of halocuprate(I)/(II) anions (e.g. [DMIM][CuBr2], DMIM = 1-dodecyl-3-methylimidazolium). A limitation concerning the preparation of a series of type II ionic liquids has been observed by the formation of the neutral compound [Cu(Im12)I]6 instead of the expected IL [Cu(Im12)2][CuI2]. The novel ILs reveal a metallo-laminate structure in the crystalline state. The salts have a liquidus range of up to 300 °C before decomposition takes place. Their catalytic properties in the synthesis of dimethyl carbonate from MeOH, CO and O2 have been studied.