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

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=Tf2 N (=N(SO2 CF3 )2- ), Nf2 N (=N(SO2 C4 F9 )2- ), FSA (=N(SO2 F)2- ), CF3 BF3- ). Salts with Tf2 N and Nf2 N were liquids, whereas those with FSA and CF3 BF3 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 Tf2 N salt to methyl iodide vapor produced ionic liquid mixtures [Rh(nBuNC)4 ]x [Rh(nBuNC)4 IMe](1-x) [Tf2 N], concomitant with a color change from purple to red, orange, and yellow, extending the thermochromic color range. The reaction of the Tf2 N salt and iodine produced mononuclear and polynuclear iodine adducts. Thus, these liquids exhibit thermochromism, fluorescence, vapochromism, chemical reactivities, and characteristic properties of ionic liquids.