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- Elding, Lars Ivar, et al.
(författare)
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A Reaction Mechanism for Oxidative Addition of Halogen to Platinum(II), Reductive Elimination of Halide from Platinum(IV) and Halide Assisted Anations of Platinum(IV) Complexes
- 1976
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Ingår i: Inorganica Chimica Acta. - 0020-1693. ; 19:2, s. 165-171
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Tidskriftsartikel (refereegranskat)abstract
- The oxidative addition of iodine to Pt(CN)42− is first-order with respect to iodide, iodine and complex. The reverse reductive elimination of iodide from trans-Pt(CN)4I22- is first-order with respect to iodide and Pt(CN)4I22−. The kinetics for the reaction between bromide and trans-Pt(CN)4ClH2O2− involves a rate-determining reductive elimination of chloride, followed by a rapid oxidative addition of bromine to the formed Pt(CN)42−. The reactions between trans-Pt(CN)4BrH2O− and bromide or chloride can be described as halide assisted anations. The rate constant for the bromide anation is kexp = k′[Br−]2 and for the chloride anation (in the presence of bromide) k′[Br−][Cl−] + k′' [Cl−]2. All reactions were followed using a stopped-flow technique at 25°C in 0.50M perchloric acid medium. The equilibrium constant for the redox equilibrium between Pt(CN)42−, iodine and Pt(CN)4I22− was determined separately to be (1.29 ± 0.03) × 104M−1. Exploratory stopped-flow experiments indicate that the oxidative addition of chlorine to PtCl42− is first-order with respect to both chlorine and tetrachloroplatinate. The experimental rate laws can be described by a reaction mechanism which resembles that introduced previously for Pt(II)-catalyzed anations and substitutions, in that both mechanisms can be considered as oxidative additions/reductive eliminations.
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- Elding, Lars Ivar, et al.
(författare)
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Bromide Anation Kinetics of Some Platinum(IV) Bromo Aqua Complexes
- 1977
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Ingår i: Inorganica Chimica Acta. - 0020-1693. ; 22:2, s. 201-207
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Tidskriftsartikel (refereegranskat)abstract
- Bromide anations of PtBr5H2O− in the presence of PtBr42− or bromine, of trans-PtBr4(H2O)2 in the presence of PtBr42− and of cis-PtBr4(H2O)2 in the presence of bromine have been studied in 0.50 M perchloric acid medium at 25 °C. The rate law for the bromide anation of PtBr5H2O−indicates two parallel reaction paths. The term k′Br−2 corresponds to a bromide assisted mechanism. The second term in the rate expression can be accounted for by assuming that a dimeric intermediate is formed from the platinum(IV) substrate and hydrated PtBr42−. The formation of the reaction product PtBr62− is preceded by a substitution of water by bromide in this dimer. A bromide assisted mechanism can also describe the bromide anation kinetics of cis-PtBr4(H2O)2, the rate law determined. The bromide anation of trans-PtBr4(H2O)2 in the presence of PtBr42− occurs by a two-term rate law, indicating two parallel paths, k′ corresponding to formation of PtBr5H2O− and k″ to formation of PtBr62−. Trans-PtBr4(H2O)2 reacts so slowly with bromide in the absence of PtBr42− that no reaction can be observed. The large difference in bromide anation rates for PtBr5H2O− and cis-PtBr4(H2O)2 compared to trans-PtBr4(H2O)2 might indicate that halide assisted anations are possible only for complexes having a halide (or some other effective bridging group) in trans-position to the aqua ligand to be replaced.
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- Elding, Lars Ivar, et al.
(författare)
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Kinetics and Mechanism for Chloride Anation of Some Platinum(IV) Aqua Complexes in the Presence of Platinum(II))
- 1976
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Ingår i: Inorganica Chimica Acta. - 0020-1693. ; 19:1, s. 31-38
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Tidskriftsartikel (refereegranskat)abstract
- Chloride anations of PtCl5H2O−, trans-PtCl4(H2O)2 and trans-Pt(CN)4ClH2O− in the presence of PtCl42− have been studied at 50°C in 1.00M perchloric acid medium. It is shown that PtCl5H2O− is formed as the primary reaction product in the two last-mentioned anations. This is not compatible with the generally used mechanism for platinum(II)-catalyzed platinum (IV) substitutions, which gives PtCl62− as the direct reaction product for these two reactions. Other examples of formation of aqua complex intermediates in previously studied platinum(II)-catalyzed platinum (IV) substitutions can be found by examination of data from the literature. The chloride anation of PtCl5H2O− follows the rate law: rate = (k′ + k″ [Cl−]) / (1 + k‴[Cl−]) x [PtCl42−][PtCl5H2O−]The usual interpretation of k‴ as the stability constant for a five-coordinate complex PtCl53− is ruled out by other experiments, which indicate a much smaller stability constant than that obtained from the kinetics. This is also supported by a stopped-flow study at 25°C in 0.5 M perchloric acid medium of the substitution of bromide by chloride in trans-Pt(NH3)4Br2 for large concentrations of entering ligand and in the presence of Pt(NH3)42+. A modified reaction mechanism is suggested which can describe all experimental results. The primary step is the formation of a dimer complex from the platinum(IV) substrate complex and the simple platinum(II) complex, hydrated in the axial positions. This dimer might decompose directly to a platinum(II) complex and a platinum(IV) aqua complex. Alternatively, it might react with the incoming ligand to form a new dinuclear complex, which decomposes to the platinum(II) complex and the substituted platinum(IV) complex.
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