Mechanistic studies of the reaction of Ir(III) porphyrin hydride with 2,2,6,6-tetramethylpiperidine-1-oxyl to an unsupported Ir-Ir porphyrin dimer.
Reaction of hydrido[5,10,15,20-tetrakis(p-tolyl)porphyrinato]iridium(III) (Ir(ttp)H) (1) with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) (2) at room temperature gave a 90% yield of the unsupported iridium(II) porphyrin dimer, Ir(II)(2)(ttp)(2) (3). Kinetic measurements revealed that the oxidation followed overall second-order kinetics: rate = k[Ir(ttp)H][TEMPO], k(25 °C) = 6.65 × 10(-4) M(-1). The entropy of activation (ΔS(‡) = -25.3 ± 2.5 cal mol(-1) K(-1)) and the kinetic isotope effect of 7.2 supported a bimolecular associative mechanism in the rate-determining hydrogen atom transfer from Ir(ttp)H to TEMPO.
Lee
Siu Yin
SY
Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, People's Republic of China.
Cheung
Chi Wai
CW
Hsu
I-Jui
IJ
Chan
Kin Shing
KS