Multifunctional Ionic Liquids from Rhodium(I) Isocyanide Complexes: Thermochromic, Fluorescence, and Chemochromic Properties Based on Rh−Rh Interaction and Oxidative Addition

Abstract

Square-planar rhodium(I) isocyanide complexes exhibit unique chemical reactivities such as the formation of Rh−Rh bonds and oxidative addition. This paper details the syntheses and properties of multifunctional ionic liquids containing RhI isocyanide complexes [Rh(nBuNC)4]X (X=Tf2N (=N(SO2CF3)2−), Nf2N (=N(SO2C4F9)2−), FSA (=N(SO2F)2−), CF3BF3−). Salts with Tf2N and Nf2N were liquids, whereas those with FSA and CF3BF3 were solids at room temperature. The salts exhibited thermochromism in the liquid state, changing from orange at high temperatures to blue-purple at lower temperatures. This is based on the equilibrium between monomer, dimer, and other oligomers associated with Rh−Rh bond formation. The salts also exhibited fluorescence. Exposure of the Tf2N salt to methyl iodide vapor produced ionic liquid mixtures [Rh(nBuNC)4]x[Rh(nBuNC)4IMe](1−x)[Tf2N], concomitant with a color change from purple to red, orange, and yellow, extending the thermochromic color range. The reaction of the Tf2N salt and iodine produced mononuclear and polynuclear iodine adducts. Thus, these liquids exhibit thermochromism, fluorescence, vapochromism, chemical reactivities, and characteristic properties of ionic liquids.