the reactions induce characteristic shifts of the stretching frequency of the coordinated carbon monoxide. These shifts are dependent on the amount of π-back bonding allowed by the newly associated ligands. The CO stretching frequencies for Vaska's complex and oxidatively added ligands have been documented in the literature. Vaska's complex: 1967 cm−1 Vaska's complex + O2: 2015 cm−1 Vaska's complex + MeI: 2047 cm−1 Vaska's complex + I2: 2067 cm−1 Oxidative addition to give Ir(III) products reduces the π-bonding from Ir to C, which causes the increase in the frequency of the carbonyl stretching band. The stretching frequency change depends upon the ligands that have been added, but the frequency is always greater than 2000 cm−1 for an Ir(III) complex. History The earliest mention of IrCl(CO)(PPh3)2 is by Vaska and DiLuzio. The closely related IrBr(CO)(PPh3)2 was described in 1959 by Maria Angoletta, who prepared the complex by the treating IrBr(CO)2(p-toluidine) with PPh3 in acetone solution. In 1957, Linda Vallerino had reported RhCl(CO)(PPh3)2. References Organoiridium compounds Carbonyl complexes Triphenylphosphine complexes Chloro complexes Substances discovered in the 1960s