Oxidation of Hypophosphorous Acid by a Ruthenium(VI) Nitrido Complex in Aqueous Acidic Solution. Evidence for a Proton-Coupled N-Atom Transfer Mechanism

作者：Li, Ji-Rui; Xu, Li-Ping; Jiang, Hui-Mei; Wang, Feng-Qin; Xie, Jianhui; Man, Wai-Lun; Wang, Qian^*; Zhuo, Shuping^*; Lau, Tai-Chu^*

来源：Inorganic Chemistry, 2022.

DOI：10.1021/acs.inorgchem.2c01627

• ELECTRON-TRANSFER
• NITROGEN ATOM
• METAL NITRIDE
• REACTIVITY
• KINETICS
• EXCHANGE
• CYCLOHEXADIENES
• AZIRIDINATION
• PHOSPHITE
• HYDROGEN

The oxidation of hypophosphorous acid (H3PO2) by a ruthenium(VI) nitrido complex, [(L)Ru-VI(N)(OH2)](+) ((RuN)-N-VI; L = N,N'-bis(salicylidene)-o-cyclohexyldiamine dianion), has been studied in aqueous acidic solutions at pH 0-2.50. The reaction has the following stoichiometry: 2[(L)Ru-VI(N)(OH2)](+) + 3H(3)PO(2) + H2O -> 2[(L)Ru-III(NH2P(OH)(2))(OH2)](+) + H3PO3. The pseudo-first-order rate constant, kobs, depends linearly on [H3PO2], and the second-order rate constant k(2) depends on [H+] according to the relationship k(2) = k[H+]/([H+] + Ka), where k is the rate constant for the oxidation of H3PO2 molecule and Ka is the dissociation constant of H3PO2. At 298.0 K and I = 1.0 M, k = (2.04 +/- 0.19) x 10(-2) M-1 s(-1) and Ka = (6.38 +/- 0.63) x 10(-2) M. A kinetic isotope effect (KIE) of 2.9 +/- 0.1 was obtained when kinetic studies were carried out with D3PO2 at pH 1.16, suggesting P-H bond cleavage in the rate-determining step. On the other hand, when the kinetics were determined in D2O, an inverse KIE of 0.21 +/- 0.03 (H3PO2 in H2O vs H3PO2 in D2O) was found. On the basis of experimental results and DFT calculations, the proposed mechanism involves an acid-catalyzed tautomerization of H2P(O)(OH) to HP(OH)(2); the latter molecule is the reacting species which reacts with RuVIN via a proton-coupled N-atom transfer pathway.

• 单位
  山东理工大学