| 1. |
- Drougge, Lise, et al.
(författare)
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Mechanisms for Acceleration of Halide Anation Reactions of Platinum(IV) Complexes. REOA versus Ligand Assistance and Platinu(II) Catalysis without Central Ion Exchange
- 1986
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Ingår i: Inorganica Chimica Acta. - 0020-1693. ; 121:2, s. 175-183
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Tidskriftsartikel (refereegranskat)abstract
- Chloride anation of trans-Pt(CN)4ClOH2− has been studied with and without Pt(CN)42− present at 25.0°C by use of stopped-flow and conventional spectrophotometry and a 1.00 M perchlorate medium. The rate law in the absence of Pt(CN)42− is compatible with a chloride assistance via an intermediate of the type Cl-Cl-Pt(CN)4···OH22−, in which the reactivity of the aqua ligand is enhanced due to a partial reduction of the platinum. This mechanism of halide assistance is in principle the same as the modified reductive elimination oxidative addition (REOA) mechanism proposed by Poë, in which the intermediate is not split into free halogen, platinum(II) and water, and in which electron transfer not necessarily involves complete reduction to platinum(II). To avoid confusion with complete reductive eliminations, reactions without split of the intermediates are here termed halide-assisted reactions. The pH-dependence indicates acid catalysis via a protonated intermediate ClClPt(CN)4···OH3−.Reaction between PtCl5OH2− and chloride is accelerated by Pt(CN)42− and gives PtCl62− as the reaction product. The rate law is derived at 35.0°C and for a 1.50 M perchlorate acid medium. The reaction takes place without central ion exchange. Alternative mechanisms with two consecutive central ion exchanges can be excluded. The role of Pt(CN)42− in this reaction is very similar to that of the assisting halide in the halide assisted anations. [p ]Reaction between trans-Pt(CN)4ClOH2− and PtCl42− gives Pt(CN)42− and PtCl5OH2− as products. The formation of an aqua complex as the primary reaction product and the rate independent of [Cl−] shows that formation of a bridged intermediate of the type Pt(II)Cl4ClPt(IV)(CN)4OH23− is formed in the initial reaction step, not five-coordinated PtCl53−.
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| 2. |
- 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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| 3. |
- Elding, Lars Ivar, et al.
(författare)
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A Tetra-Nitrato Complex of Platinum(II), Synthesis and Crystal Structure of K2[Pt(NO3)4].1/2H2O
- 1985
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Ingår i: Inorganica Chimica Acta. - 0020-1693. ; 103:2, s. 127-131
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Tidskriftsartikel (refereegranskat)abstract
- K2[Pt(NO3)4]·Full-size image (<1 K)H2O was prepared from ca 0.4 M solutions of platinum(II) perchlorate in perchloric acid by addition of KHCO3 and KNO3. Its crystal structure was determined from X-ray intensity data collected with a CAD-4 diffractometer. Monochromatic MoKα-radiation was used. The space group is I4/m with Z = 4; a = 7.5277(4) and c = 20.470(3) Å. The refinement converged to R = 0.036. The structure contains discrete complexes, [Pt(NO3)4]2−, with symmetry C4. Pt coordinates four O from different unidentate nitrato groups. The PtO distance is 2.010(5) Å. The coordination around Pt is distorted square-planar, with Pt situated 0.14 Å above the plane formed by four O, so that a very flat, square pyramid is formed. Two such pyramids on each side of the mirror plane are packed together with their bases facing each other. The closest OO distance between them is 3.29(1) Å and the PtPt distance is 3.590(1) Å. The potassium ions are located between the pairs of complexes so that a three-dimensional packing of K+ and 2×[Pt(NO3)4]2− is formed.
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| 4. |
- 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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| 5. |
- 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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| 6. |
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| 7. |
- Elding, Lars Ivar
(författare)
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Palladium(II) Halide Complexes I. Stabilities and Spectra of Palladium(II) Chloro and Bromo Aqua Complexes
- 1972
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Ingår i: Inorganica Chimica Acta. - 0020-1693. ; 6, s. 647-651
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Tidskriftsartikel (refereegranskat)abstract
- Stability constants, βn, n = 1, 2, 3, 4, for the chloro and bromo complexes of palladium(II) have been calculated, using a least squares programme, from spectrophotometric measurements at 222, 234.5 and 279 nm (chloride) and at 247, 265, and 332 nm (bromide). The following values of lg(βn/M−n) were obtained: 4.47±0.01, 7.76±0.04, 10.17±0.07, and 11.54±0.09 (chloride) and 5.17±0.02, 9.42±0.04, 12.72±0.06, and 14.94±0.08 (bromide). Spectra of the species PdXn(H2O)4−n2−n, n = 0, 1, 2, 3, 4; X = Cl, Br, have been determined in the wave length region 210 to 600 nm. The temperature was 25.0°C and the ionic medium 1.00 M perchloric acid.
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| 8. |
- Elding, Lars Ivar
(författare)
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Palladium(II) Halide Complexes II. Acid Hydrolysis and Halide Anations of Palladium(II) Chloro and Bromo Aqua Complexes
- 1972
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Ingår i: Inorganica Chimica Acta. - 0020-1693. ; 6, s. 683-688
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Tidskriftsartikel (refereegranskat)abstract
- The rate constants for the chloride and bromide anations of Pd(H2O)42+, the chloride anations of PdCl3H2O−, the bromide anation of PdBr3H2O− and the acid hydrolysis of PdCl(H2O)3+, PdBr(H2O)3+, PdCl42−, and PdBr42− have been determined at 15, 25 and 35 °C using a stopped-flow technique. The ionic strength was 1.00 M and the supporting electrolyte perchloric acid. The obtained rate constants and the activation enthalpies and entropies are given. A comparison with the corresponding reactions for platinum(II) complexes indicates that the acid hydrolyses are 1×105 to 2×105 times faster and the halide anations 4×101 to 6×104 times faster for palladium. The increased rates of reaction are due to a decrease in activation enthalpies. The reactions are typically square planar substitutions with respect to entering and leaving groups. The mechanism appears to be associative in nature.
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| 9. |
- Elding, Lars Ivar
(författare)
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Palladium(II) Halide Complexes III. Acid Hydrolyses and Halide Anations of cis- and trans-Dichlorodiaquapalladium(II) and -Dibromoaquapalladium(II))
- 1973
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Ingår i: Inorganica Chimica Acta. - 0020-1693. ; 7, s. 581-588
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Tidskriftsartikel (refereegranskat)abstract
- Chloride and bromide anations of PdX(H2O)3+, cis-PdX2(H2O)2 and trans-PdX2(H2O)2, acid hydrolyses of PdX3H2O−, cis-PdX2(H2O)2 and trans-PcX2(H2O)2, X = Cl, Br, have been studied at different temperatures by means of a stopped-flow technique. Rate constants and activation parameters are given. The palladium complexes react about 5×104 to 5×105 times faster than the analogous platinum(II) complexes. The activation enthalpies are 8 to 10 kcal mol−1 smaller for palladium. A simple model for description of the rates of acid hydrolyses and halide anations of palladium(II) and platinum(II) halide complexes by cis-, trans-, and ionic charge effects is introduced. For palladium, the relative trans-effect Cl/H2O is about 50 and Br/H2O about 500. The relative cis-effect H2O/ Cl is about 4 and H2O/Br about 8. The trans-effects are 6 times smaller than for corresponding platinum complexes, the cis-effects somewhat greater. The equilibrium between cis-PdX2(H2O)2 and trans-PdX2(H2O)2 has been studied. The cis-isomer is the predominant species at equilibrium, the equilibrium constant cis/trans being 2.1±0.3 for X = Cl and 6.0± 0.8 for X = Br at 25°C. The ionic strength was 1.00 M and the supporting electrolyte perchloric acid.
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| 10. |
- Elding, Lars Ivar, et al.
(författare)
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Platinum(IV) Bromo Aqua Complexes. Acid Hydrolysis Equilibria and Kinetics of Bromiide Anation
- 1971
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Ingår i: Inorganica Chimica Acta. - 0020-1693. ; 5, s. 643-649
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Tidskriftsartikel (refereegranskat)abstract
- The stepwise stabililty constants, Kn for the bromo aqua complexes PtBrn−1(H2O)7−n5−n; n=4, 5, 6, formed in the successive acid hydrolyses of PtBr62−, have been determined to be K6=(.19±0.1) x 103 M−1, K5= (1.0±0.2) x 104 M−1 and K4=(1.1±0.2) x 105 M−1. A bromide assisted mechanism is proposed for the bromide anations of PtBr4(H2O)2 and PtBr5H2O-. Both these reactions are found to be first order with respect to platinum complex. The dependence of the observed rate constant on the bromide concentration can be described by the eqn. kexp=κ′[Br−]+κ″[Br−]2The last term is probably due to a reaction path via a bromide associated outer sphere complex, which might also be involved in the path described by the first term. A spectrophotometric method has been used. To suppress the protolysis of the aqua complexes, 0.50 M perchloric acid was used as the ionic medium. The temperature was 25.0 °C.
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