Siu Yin Lee

Publications (3)4.6 Total impact

• Article: 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.

  Siu Yin Lee, Chi Wai Cheung, I-Jui Hsu, Kin Shing Chan
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  ABSTRACT: 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.
  Inorganic Chemistry 10/2010; 49(20):9636-40. · 4.60 Impact Factor
• Article: Reactivity Studies of Iridium(III) Porphyrins with Methanol in Alkaline Media

  Chi Wai Cheung, Hong Sang Fung, Siu Yin Lee, Ying Ying Qian, Yun Wai Chan, Kin Shing Chan
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  ABSTRACT: Ir(ttp)Cl(CO) (1a; ttp = 5,10,15,20-tetrakis(p-tolyl)porphyrinato dianion) was found to cleave the C−O bond of CH3OH at 200 °C to give Ir(ttp)CH3 (3a). Addition of KOH promoted the reaction rate and gave a higher yield of Ir(ttp)CH3 in 70% yield in 1 day. Mechanistic studies suggest that, in the absence of KOH, Ir(ttp)Cl(CO) reacts with CH3OH initially to give Ir(ttp)OCH3, which then undergoes β-hydride elimination to produce Ir(ttp)H (4a). Ir(ttp)H further reacts slowly to cleave the C−O bond of CH3OH, likely via σ-bond metathesis, to give Ir(ttp)CH3. In the presence of KOH, Ir(ttp)Cl(CO) initially reacts with KOH more rapidly to give Ir(ttp)OH, which then cleaves the O−H bond of CH3OH by metathesis to give Ir(ttp)OCH3. Ir(ttp)OCH3 further isomerizes via β-hydride elimination/reinsertion to give Ir(ttp)CH2OH and concurrently undergoes base-assisted β-proton elimination to give Ir(ttp)−K+ (5a). Ir(ttp)CH2OH subsequently condenses with CH3OH to form Ir(ttp)CH2OCH3 (2). Finally, Ir(ttp)−K+ cleaves the C−O bond in CH3OH, most probably via nucleophilic substitution, to give Ir(ttp)CH3. Ir(ttp)CH2OCH3 also serves as the precursor of Ir(ttp)−K+ as it undergoes nucleophilic substitution by KOH to give Ir(ttp)−K+.
  02/2010;
• Article: Reactivity Studies of Rhodium(III) Porphyrins with Methanol in Alkaline Media

  Hong Sang Fung, Yun Wai Chan, Chi Wai Cheung, Kwong Shing Choi, Siu Yin Lee, Ying Ying Qian, Kin Shing Chan
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  ABSTRACT: Rh(ttp)Cl (1a) (ttp = 5,10,15,20-tetrakistolylporphyrinato dianion) was found to react with methanol at a high temperature of 150 °C in the presence of inorganic bases to give a high yield of Rh(ttp)CH3 (2a), up to 87%. Rh(ttp)H (1d) is suggested to be the key intermediate for the carbon−oxygen bond cleavage.
  07/2009;