ENTHALPY CHANGES IN OXIDATIVE ADDITION-REACTIONS OF RHODIUM(I) AND IRIDIUM(I) COMPLEXES

Titration calorimetric methods have been used to determine enthalpies of oxidative addition reactions of iodine, tetrachloro-1, 2-benzoquinone, tetracyanoethylcne, sulfur dioxide, and dimethyl acctylenedlcar boxy late with rhodium and iridium complexes of the type trans-[MX(CO)L2] in benzene solution, X represents an anion and L represents triphcnylarsine or a series of tertiary phosphorus ligands spanning a range of cone angles, θ, from 107 to 170° and a range of electronic parameters, v (after C. A. Tolman), from 2056.4 to 2085.3 cm-1. The data have been fitted to an empirical relation of the type -ΔH = A0 + A1θ + A2v. Single parameter correlations were also attempted. Enthalpies for additions to trans-[MCl(CS)PPh3)2] were obtained for comparison with those of the carbonyl analogues. Enthalpies for addition of I2, C2(CN)4, and o-O2C6Cl4 to trans-[IrCl(CO)(PPh3)2 were also measured in the solvents 1, 2-dichloroethane and acetonitrile (I2 only). Enthalpies for the addition of HCl, HBr, Cl2, Br2, o-(O2)C6H4SCl, and o-(O2N)C6H4CH2C(O)Cl to Vaska's complex and in some cases trans-[IrCl(CO)(PMePh2)2] were measured in benzene. The Cl2, Br2, and I2 data were used to calculate approximations of the iridium-halogen bond energies. A new preparation for the complex trans-[IrCl(CO)(PMe2Ph)2] has been developed. © 1979, American Chemical Society. All rights reserved.