Reversible C-60 binding to dendrimer-containing Ir(CO)Cl(PPh(2)R)(2) complexes

The phosphine compounds PPh(2)(G-1) and PPh(2)(G-2), where G-1 is 3,5-bis(benzyloxy)benzyl and G-2 is 3,5-bis((3,5-bis(benzyloxy)oxy)benzyl, were synthesized. The complexes, trans-Ir(CO)Cl(PPh(2)(G-1))(2), 1, and trans-Ir(CO)Cl(PPh(2)(G-2))(2), 2, show reversible binding with C-60. Thermodynamic data on the reversible binding were obtained in chlorobenzene by line width analysis of the P-31{H-1} NMR spectra. The activation parameters Delta G(265)(double dagger) (kcal mol(-1)), Delta H-double dagger (kcal mol(-1)), and Delta S-double dagger (cal mol(-1) K-1) were calculated as 1.3, 18, and 20 for 1 . C-60 and 1.3, 24, and 42 for 2 . C-60. The thermodynamic quantities Delta G(265)degrees (kcal mol(-1)), Delta H degrees (kcal mol(-1)), and Delta S degrees (cal mol(-1) K-1) were determined to be -2.8, -25, and -105 for 1 . C-60 and -3.0, -18, and -57 for 2 . C-60. The rates of reaction with O-2 for 1 and 2 were measured and are comparable to that for trans-Ir(CO)Cl(PPh(3))(2) under similar conditions. The compound PdI2(PPh(2)(G-1))(2), 3, does not show reversible binding with C-60. Crystal structures were obtained for 1 (a = 10.218(1) Angstrom, b = 12.731(3) Angstrom, c = 13.116(2) Angstrom, alpha = 112.05(1)degrees, beta = 108.30(1)degrees, gamma = 102.22(1)degrees, V = 1392.2(4) Angstrom(3)) and 3 (a = 10.243(2) Angstrom, b = 12.689(2) Angstrom, c = 13.146(2) Angstrom, alpha = 112.33(1)degrees, beta = 108.96(1)degrees, gamma = 101.23(1)degrees, V = 1392.4(4) Angstrom(3)).