Spectroscopic investigations of catalytic iridium carbonyl species in sodium chloroaluminate melts

Abstract

In situ spectroscopic studies of the iridium chemistry occurring during the catalytic hydrogenation of carbon monoxide employing IrCl(CO) 3 and Ir 4(CO) 12 in an aluminum chloride-sodium chloride (63:37 mole%) melt were performed. Infrared, UV-visible, Raman, and 1H NMR data indicate that similar monomeric species are generated during catalysis. Infrared investigation of the introduction of IrCl(CO) 3 into molten AlCl 3:NaCl (63:37) under CO:H 2 (1:3 mole ratio) and the reaction between IrCl(CO) 3 and carbon monoxide in an acidic melt suggest the initial formation of an iridium-carbonyl species followed by the generation of a hydridocarbonyl complex in the initial stage of the catalysis. Infrared data also indicate that the method of introduction for Ir 4(CO) 12 into the AlCl 3:NaCl medium under 1 atm of CO:H 2 (1:3 mole ratio) has a marked effect on the spectra observed. In an acidic melt IrCl(CO) 3 reacts with hydrogen to form hydrogen chloride, methane and metallic iridium.