Mechanism for the formation and structure of the iodoplatination product of propargyl acid in the Pt(IV)-I−-H2O system

Propargyl alcohol in aqueous Pt(IV) iodide solutions at 10–15°C gives the product of the addition of Pt^IV and iodide to the triple bond, isolated as Pt^IV(CH=Cl-CH₂OH)₂I₂(CH₃OH). The vinyl ligands in this complex are in cis position. The complex decomposes at 80°C to give E,E-2,5-diiodo-2,4-hexadiene-1,6-diol and PtI₂. The E, E structure of the diene indicates trans addition of Pt^IV and I^– to the alkyne in the iodoplatination steps.L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg St., 340114 Donetsk, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 4, pp. 234–237, July–August, 1996. Original article submitted October 17, 1995.     

Kinetics of tetraamminecopper(II)-catalysed oxidation of sulphur(IV) by peroxodisulphate in ammonia buffer

The kinetics of tetraamminecopper(II)-catalysed oxidation of SO^2– ₃ to SO^2– ₄ in ammonia buffers and in a nitrogen atmosphere obeys the rate law: –d[S^IV]/dt = k ₂[Cu^II][SO₃ ^2–][NH₃]^–1. There is spectrophotometric evidence for the formation of the intermediate complex [Cu(NH₃)₃(SO₃)] in a pre-equilibrium.     

Modeling water exchange on monomeric and dimeric Mn centers

Water exchange on Mn centers in proteins has been modeled with density functional theory using the B3LYP functional. The reaction barrier for dissociative water exchange on [Mn^IV(H₂O)₂(OH)₄] is only 9.6 kcal mol^–1, corresponding to a rate of 6×10⁵ s^–1. It has also been investigated how modifications of the model complex change the exchange rate. Three cases of water exchange on Mn dimers have been modeled. The reaction barrier for dissociative exchange of a terminal water ligand on [(H₂O)₂(OH)₂Mn^IV(-O)₂Mn^IV(H₂O)₂(OH)₂] is 8.6 kcal mol^–1, while the bridging oxo group exchange with a ring-opening mechanism has a barrier of 19.2 kcal mol^–1. These results are intended for interpretations of measurements of water exchange for the oxygen evolving complex of photosystem II. Finally, a tautomerization mechanism for exchange of a terminal oxyl radical has been modeled for the synthetic O₂ catalyst [(terpy)(H₂O)Mn^IV(-O)₂Mn^IV(O)(terpy)]³⁺ (terpy=2,2:6,2-terpyridine). The calculated reaction barrier is 14.7 kcal mol^–1.Contribution to the Björn Roos Honorary Issue     

Kinetics and mechanism of silver(I) catalysed autoxidation of aqueous sulphur(IV) in acetate buffered medium

The kinetics of the silver(I) catalysed autoxidation of aqueous sulphur(IV) an acetate buffered medium obey the rate law: –d[S^IV]/dt = D[Ag^I][S^IV]²[H⁺]^–1/(B+C[S^IV]). The rate is independent of [O₂] but strongly inhibited by EtOH. A free radical mechanism is proposed.     

Cesium dimethyltetrachloroplatinate,a complex of dimethylplatinum(IV). Synthesis and some reductive elimination reactions involving the monomethylplatinum(II) complex as an intermediate

The reduction of Pt(IV) complexes followed by the oxidative addition of dimethyl sulfate to Pt(II) affords Cs₂PtMe₂Cl₄, a complex of dimethylplatinum(IV). On treatment with such nucleophiles as Cl^–, Br^–, I^–, and PtCl₄ ^2– in aqueous solutions at 368 K this complex undergoes reductive elimination to give MeX and Pt^IIMe as a transient species. The latter is further converted to methane upon protolysis, whereas in the presence of an oxidant (Na₂PtCl₆) it gives rise to the Pt^IVMe species. The kinetics of decomposition of Cs₂PtMe₂Cl₄ in aqueous HCl-KCl systems (2M or 3M in Cl^–; [Pt^IVMe₂][Cl^–]) were studied. The reaction takes place as anS _N 2 attack of X^– on the carbon atom of a methyl group located with thetrans position with respect to the aqua-ligand of the [PtMe₂Cl₃(H₂O)]^– complex.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 389–395, February, 1993.     

Mechanism of oxidation of selenium(IV) by cobalt(III) in perchloric acid — a kinetic study

Summary The kinetics of Co^III oxidation of Se^IV have been studied in aqueous HClO₄. The order with respect to Co^m is two the order with respect to Se^IV is one at low concentrations; two at high concentrations. The latter variation is attributed to the greater reactivity of the Se^IV dimier A mechanism involving complexation between oxidant and substrate is proposed. [CoOH]²⁺ is presumed to be the reactive Co^III species and H₂SeO₃ and HSeO ₃ ^– to be those of Se^IV. At 25° C, E_a, H and S for the monomeric path are 125.6±4.0 kJ mol^–1, 122.1±3.8 kJ mol^–1 and 206±12 JK^–1 mol^–1 respectively and those for the dimeric path are 88.6±3.6 kJ mol^–1, 85.9±3.4 kJ mol^–1 and 62.6±11.3 JK^–1 mol^–1 respectively.     

Kinetics and Mechanism of the oxygenation of triphenylphosphine by bis(ethyl-L-cysteinato)dioxomolybdenum(VI)

Summary The kinetics of oxygen-transfer from [MoO₂(Et-L-cys)₂] to PPh₃ and the reaction between [Mo₂O₃(Et-L-cys)₄] and O₂ in benzene solution have been investigated using spectrophotometric techniques between 25 and 40°. The rate laws-d[Mo⁶⁺]/dt = k₁[Mo⁶⁺][PPh₃] with k₁ (at 35°) = 2.95×10^–4dm³mol^–1s^–1 and -d[Mo⁵⁺]/dt = 2k₃[Mo⁵⁺][O₂] with k₃ (at 35°) = 6.3×10^–2 dm³mol^–1s^–1 account for the kinetic data obtained with activation parameters (at 35°) of H = 46 kJ mol^–1, S = –153 JK^–1mol^–1, and H = 50.8 kJ mol^–1, S = –95 JK^–1 mol^–1 respectively.     

The reactivity of cis-platin. Spectroscopic properties of products isolated from the [cis-Pt(NH3)2Cl2–quercetin] and [cis-Pt(NH3)2Cl2–CrVI–quercetin] systems

New coordination compounds: [Pt^IIQ] and [Pt^IV–Cr^IIIQ₂], where Q = quercetin, were isolated from the [Pt(NH₃)₂Cl₂–quercetin] and [Pt(NH₃)₂Cl₂–Cr^VI–quercetin] systems, respectively. Structures are proposed on the basis of i.r., n.m.r. and deconvoluted electronic spectra.     

Pulse radiolysis investigations on the reactions of primary radiolytic species of water with atropine

On pulse radiolysis of N₂O saturated aqueous solutions of atropine, an optical absorption band (_max at 320 nm,e=2.81·10³ dm³·mol^–1·cm^–1) was observed, which is assigned to the product of reaction of OH radicals with the solute. This absorption decayed following second order kinetics with a rate constant of 4.5·10⁸ dm³·mol^–1·s^–1. The rate constant for the reaction of OH radicals with atropine as estimated by following the build-up kinetics is 2.7·10⁹ dm³·mol^–1·s^–1. The H atoms also reacted with this compound to produce a transient absorption band behaving similarly to the one observed in the case of reaction with OH radicals. The transient species formed in both cases is assigned to a radical derived by H atom abstraction by H/OH radicals from the parent compound. This radical was unreactive towards 2-mercaptoethanol. e _aq ^– was found to react with atropine forming a transient band with _max at 310 nm (=3.55·10³ dm³·mol^–1). Its decay was also second order with a rate constant of 1.64·10⁹ dm³·mol^–1·s^–1. The bimolecular rate constant for the reaction of e _aq ^– with atropine as estimated from the decay of e _aq ^– absorption at 720 nm is 3.9·10⁹ dm³·mol^–1·s^–1. Specific one-electron oxidizing and reducing agents (such as Cl ₂ ^– , Tl²⁺, SO ₄ ^– and (CH₃)₂COH, CO ₂ ^– , respectively) failed to oxidize or reduce this compound in aqoues solutions. The radical anion of atropine formed by its reaction with e _aq ^– was found to reduce thionine and methyl viologen with bimolecular rate constant of 3.8·10⁹ and 3.2·10⁹ dm³·mol^–1·s^–1, respectively.     

Facile generation of platinum(IV) compounds with mixed labile moieties. Hydrogen peroxide oxidation of platinum(II) to platinum(IV) compounds

Hydrogen peroxide oxidation of platinum(II) compounds containing labile groups such as Cl, OH, and alkene moieties has been carried out and the products characterized. The reactions of [Pt^II (X)₂ (N–N)] (X = Cl, OH, X₂ = isopropylidenemalorate (ipm); N–N 2,2-dimethyl-1,3-propanediamine [(dmpda), N-isopropyl-1,3-propanediamine (ippda)] with hydrogen peroxide in an appropriate solvent at room temperature affords [Pt^IV (OH)(Y)(X)₂(N–N)] (Y = OH, OCH₃). The crystal structures of [Pt^IV(OH)(OCH₃)(Cl)₂(dmpda)]·2H₂O (P-1 bar, a = 6.339(2) Å , b = 9.861(1) Å, c = 11.561(1) Å, a = 92.078(9)°, β = 104.78(1)°, γ=100.54(1)°, V = 684.3(2) ų, Z = 2R = 0.0503) and [Pt^IV(OH)₂(ipm)(ippda)]·3H₂O (C 2/c, a = 27.275(6) Å, b=6.954(2) Å, c = 22.331(4) Å, β = 118.30(2)°, V = 3729(2) ų, Z = 8, R = 0.0345) have been solved and refined. The local geometry around the platinum(IV) atom approximates to a typical octahedral arrangement with two added groups (OH and OCH₃; OH and OH) in a transposition. The platinum(IV) compounds with potential labile moieties may be important intermediate species for further reactions.     

Reactions of sulfur(IV) with an octahedral manganese(IV) complex of 1,8-bis(2-hydroxy benzamido)-3,6-diaza octane: the role of phenolate–amide–amine coordination

The Mn^IV complex of tetra-deprotonated 1,8-bis(2-hydroxybenzamide)-3,6-diazaoctane (Mn^IVL) engrossed in phenolate-amido-amine coordination is reduced by HSO₃⁻ and SO₃²⁻ in the pH range 3.15–7.3 displaying biphasic kinetics, the Mn^IIIL⁻ being the reactive intermediate. The Mn^IIIL⁻ species has been characterized by u.v.–vis. spectra {λ _max, (ε, dm³ mol⁻¹ cm⁻¹): 285(15 570), 330 sh (7570), 469(6472), 520 sh (5665), pH=5.42}. SO₄²⁻ was the major oxidation product of S^IV; dithionate is also formed (18 ± 2% of [Mn^IV]_T) which suggests that dimerisation of SO₃^−• is competitive with its fast oxidation by Mn^IV/III. The rates and activation parameters for Mn^IVL + HSO₃⁻ (SO₃²⁻) → Mn^IIIL⁻; Mn^IIIL⁻ + HSO₃⁻ (SO₃²⁻) → Mn^IIL²⁻ are reported at 28.5–45.0 °C (I=0.3 mol dm⁻³, 10% (v/v) MeOH + H₂O). Reduction by SO₃²⁻ is ca. eight times faster than by HSO₃⁻ both for Mn^IVL and Mn^IIIL⁻. There was no evidence of HSO₃⁻/SO₃²⁻ coordination to the Mn centre indicating an outer sphere (ET) mechanism which is further supported by an isokinetic relationship. The self exchange rate constant (k₂₂) for the redox couple, Mn^IIIL⁻/Mn^IVL (1.5 × 10⁶ dm³ mol⁻¹ s⁻¹ at 25 °C) is reported.     

Platinum(IV) complexes of reducing sugars in an alkaline medium and their resistance to reaction with N-bromosuccinimide. A kinetic study

Spectrophotometric studies support the formation of { Pt^IV–S} (where S = glucose, galactose and fructose) complexes in an alkaline medium. The resistance of these complexes to reaction with N-bromosuccinimide (NBS) has been observed. The kinetic data also support the formation of { Pt^IV –S} complexes.     

Kinetics and mechanism of oxidation of tellurium(IV) by cobalt(III) in perchloric acid

Summary The kinetics of oxidation of Te^IV by Co^III have been studied in aqueous HClO₄. A mechanism presuming [Co(OH₂)₅(OH)]²⁺ to be the reactive species has been proposed, which leads to the rate-equation shown. Rate=–d[Co^III]/dt=2kKK _h ² [Co^III] _t ² [Te^IV]/[H⁺]² K_b is the hydrolysis constant of Co^III, K is the formation constant of the complex between Co^III and Te^IV and k is the rate of decomposition of that complex. E_a and S are 95.0±2.1 kJ mol^–1 and 28.3±7.1 JK^–1 mol^–1, respectively.     

Reduction Process of Tetraplatin in the Presence of Deoxyguanosine Monophosphate (dGMP): A Computational DFT Study

The reduction mechanism of [Pt^IV(dach)Cl₄] (dach=diaminocyclohexyl) in the presence of dGMP was studied. The first step is substitution of a chloro ligand by dGMP, followed by nucleophilic attack of a phosphate or sugar oxygen atom to the C8‐position of guanine. Subsequent reduction forms the [Pt^II(dach)Cl₂] complex. The whole process is completed by a hydrolysis. Two different pathways for the substitution reaction were examined: a direct associative and a Basolo–Pearson autocatalytic mechanism. All the explored structures were optimized at the B3LYP‐D3/6‐31G(d) level and by using the COSMO solvation model with Klamt's radii. Single‐point energetics was determined at the B3LYP‐GD3BJ/6‐311++G(2df,2pd)/PCM/scaled‐UAKS level. Activation barriers were used for an estimation of the rate constants and these were compared with experimental values. It was found that the rate‐determining step is the nucleophilic attack with a slightly faster performance in the 3′‐dGMP branch than in the case of 5′‐dGMP with activation barriers of 21.1 and 20.4 kcal mol^?1 (experimental: 23.8 and 23.2 kcal mol^?1). The reduction reaction is connected with an electron flow from guanine. The product of the reduction reaction is a chelate structure, which dissociates within the last reaction step, that is, a hydrolysis reaction. The whole redox process (substitution, reduction, and hydrolysis) is exergonic by 34 and 28 kcal mol^?1 for 5′‐dGMP and 3′‐dGMP, respectively.     

Chromium(VI), chromium(V) and chromium(IV) oxidation of 12-tungstocobaltate(II)

The reaction between Cr^VI and 12-tungstocobaltate(II) was carried out in 2.0 mol dm^–3 HCl and followed a simple second order rate law. The reaction was catalysed by hydrogen ion due to the formation of active H₂CrO₄ and was inhibited by chloride ion as, in its presence, conversion of the active species into inactive chlorochromate occurs. Chromium(V) and chromium(IV) were generated in situ by the use of Cr^VI—V^IV or Cr^VI—2-ethyl-2-hydroxybutyric acid and Cr^VI—i-PrOH reactions respectively, and the oxidation of 12-tungstocobaltate(II) by these atypical oxidation states, was also studied. The rate constants for the oxidation of 12-tungstocobaltate(II) by Cr^VI, Cr^V and Cr^IV were found to be in the ratio 1:1.2:5.2 respectively. The ionic strength did not affect the reaction, while decrease in the solvent polarity increased the rate of the reaction. The activation parameters were also determined and the values H , G and S were found to be 52.4 ± 6 kJ mol^–1, 100.8 ± 7 kJ mol^–1, –151.7 ± 10 J K^–1 mol^–1 respectively, supporting the mechanism proposed.     

Oxidative cleavage of α, β-unsaturated compounds by pentachlorohydroxoplatinate(IV) in alkaline medium

The kinetics of oxidation of α,β-unsaturated compounds by platinum(IV) in the presence of alkali {[OH⁻]= (1–9) × 10⁻³ mol dm⁻³} have been investigated over the 303–318 K temperature range . The rate of the reaction is dependent on the first power of the concentrations of substrates, oxidant, and alkali. The rate constant increases with an increase in ionic strength and also with increasing dielectric constant of the medium. The oxidation rates follow the order: –CN > –CONH₂ > –COO⁻. The values of the third order rate constant (k₃) for the oxidation of acrylonitrile, acrylamide and acrylate are 1.24, 0.826 and 0.628 mol⁻² dm⁶ s⁻¹ respectively, at 303 K. The oxidations of the substrates by PtCl₅(OH)²⁻ take place by an inner-sphere mechanism. Platinum(IV) is reduced to platinum(II) by the substrates in a one-step two-electron transfer process to give reaction products. The major reaction product, HCHO, is identified from the reaction mixture using i.r. spectrometry, n.m.r. and C, H, N analysis. A tentative reaction mechanism, leading to the formation of products, has been suggested. The activation parameters of the reaction have been evaluated.     

Kinetics and mechanism of the oxidation of [N-(2-hydroxy-ethyl)ethylenediamine-N,N′,N′-triacetatocobalt(II)] by vanadate ion

The kinetics of oxidation of Co^IIHEDTA {HEDTA = N-(2-hydroxyethyl)ethylenediamine-N,N,N-triacetic acid} by vanadate ion have been studied in aqueous acid in the pH range 0.75–5.4 at 43–57 °C. The reaction exhibits second-order kinetics; first-order in each of the reactants. The reaction rate is a maximum at pH = 2.1. A mechanism is proposed in which the species [Co^IIHEDTA(H₂O)]^– and VO₂ ⁺ react to form an intermediate which decompose slowly to give pentadentate Co^IIIHEDTA(H₂O) and V^IV as final products. The rate law was derived and the activation parameters calculated: H* = 26.96 kJ mol^–1 and S* = –311.08 JK^–1 mol^–1.     

Kinetics and mechanism of exchange reaction of [Y(APTA)] (APTA=o-aminophenol-N,N, O-triacetic acid) with copper(II)

Summary The kinetics of the exchange reaction between [Y(APTA)] and Cu^II have been investigated over a range of [H⁺] from 2.5×10^–5 to 7.5×10^–4 mol dm^–3 at 30°C and ionic strength 0.2 mol dm^–3 KNO₃. The results show that the exchange reaction proceeds via both self-and proton-catalyzed dissociation of [Y(APTA)] and also by the direct attack of Cu^II on [Y(APTA)]. The corresponding rate constants k_d, k _h and k_Cu have been evaluated as 6.3s^–1, 8.4×10⁴ mol^–1 dm³ s^–1 and 416mol^–3 dm³ s^–1 respectively. The possible intermediates are discussed in terms of the structure of APTA. The complex-formation rate constants of Y^III with APTA^3- and HAPTA^2- were also obtained.     

Rate and stoichiometry of the fast gas titration reaction HCO + O2 → CO + HO2

The title reaction has been investigated by the FD/LMR technique at room temperature. The rate constant of the overall reaction was estimated to be 2.6×10¹² cm³ mol^–1 s^–1. The yield of HO₂ formation was found to be unity, 1.00±0.05.     

Spectral and kinetic characteristics of the α-propionic acid methyl ester radical in cyclohexane and water

The -propionic acid methyl ester radical was produced in dissociative electron capture reaction of 2-chloropropionic acid methyl ester. The absorption maxima of the radical are at 310 and 300 nm in cyclohexane and water with extinction coefficients of 440±50 and 400±50 mol^–1 dm³ cm^–1. The second order decay rate parameter in water is (2.3±0.5)×10⁹ mol^–1 dm³ s^–1. The peroxy radicals have the characteristics: _max=265–270 nm, _max=700–900 mol^–1 dm³ and 2k=(7±2)·10⁸ mol^–1 dm³ s^–1.