Tuning Reactivity of Platinum(II) Complexes

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dinuclear Pt(II) complexes to release the bridging ligand and form [Pt(TU)4] 2+ . This could only be achieved in presence of excess added thiourea and its derivatives. The results of temperature-dependence measurements are in agreement with expectations for d 8 square-planar Pt(II) complexes. All the values for the entropies of activation are largely negative and support an associative mode of substitution mechanism. In Chapter 5, the work in chapter 4 was extended to include rigid diazine-bridged dinuclear Pt(II) complexes of the type [{cis–Pt(NH3)2(H2O)}2–μ–z] +4, (z = diazine heterocyclic ring like pyrazine, pyrimidine, pyridazine and related benzodiazines, which differ in the relative disposition of the two Pt(II) centres. A comparison of the second order rate constants, k2(1 st /2 nd ), at 25 °C, obtained for consecutive substitution of the aqua ligands shows the reactivity of the complexes decreases as the Pt---Pt distance decreases from being para to each other in pzn to ortho disposition in pdn. This demonstrates that the steric effect increases with decreasing Pt---Pt distance among the diazine complexes. The effect of increasing or decreasing the electron density of the Pt(II) centre is also visible in the pKa values, which is attributed to π-resonance properties of the diazine linkers and the relative longer distances between the Pt(II) centres. In comparison the benzodiazine bridged complexes qzn and pht have better π-acceptor characteristics relative to pmn and pdn. The net result is that the Pt-metal of qzn is more electropositive and as such is more reactive than pmn as a result of the stronger π- backbonding of the diazine ring system. But the N=N bond in phthalazine (pht) ligand is strongly electron-withdrawing from the introduced aromatic ring. This makes it a net σ- inductive electron donor. Hence, the σ-donicity of the pht-bridge causes the opposite effect, by making the metal centre for pht more electronegative or less electrophilic than the rest of the complexes. As such it is the least reactive. 1H NMR spectroscopy was applied to study the reactions of pzn–Cl and aqua pdn complexes with thiourea. The stability of the chloro complex was higher than was measured for the aqua complex. 1H and 195Pt NMR studies again revealed the release of linker and the formation of the corresponding PtS4 units in the third step. At pH 2.0, this 3
process is accelerated by protonation of the freed terminal N atoms of the bridging ligand, which prevents re-attachment to the metal centre. All the values of the activation entropies are negative and confirm the associative character of the nucleophilic substitution mechanism. In Chapter 6, thermodynamic and kinetic properties of relatively new diaqua Pt(II) complexes of the type [{cis–Pt(NH3)2(H2O)}2L] +4 (L = 4,4`-bis(pyridine)sulphide, 4,4’- bis(pyridine)disulphide or 1,2-bis(4-pyridyl)ethane ) were studied for the first time. The study mainly focused on the influence of the spacer group and its effect on nucleophilic substitution reactions. The results indicate that there is electronic communication between the two platinum centres leading to two pKa values. The thermodynamic data obtained demonstrates that the pKa values of the coordinated aqua moieties are dependent on the nature of the linker. Clearly, higher pKa values were obtained as the Pt- --Pt separation distance becomes longer showing that the effectiveness of localised charge additions at the Pt(II) centres decreases as the distance is increased further. The pKa2 values of the second deprotonation step are also influenced by nature of spacer group, whereby S-based spacers are stronger σ-donors which impacts negatively on the acidity of the second coordinated water molecule. This resulted in bigger pKa2 values as the number of S atoms was increased. It is also demonstrated by these investigations that the nature of the bridge has a strong influence on the reactivity of the complexes. The results of the substitution reactions with anions and thiourea nucleophiles of the corresponding diaqua complexes performed at pH 2 were explained in terms of the adopted symmetry by the different dinuclear complexes. The repulsions between the two lone pairs on S atom and the pyridine rings prevent Pt1 to adopt a perfect C2v symmetry. The DFT calculations clearly demonstrated that due to non-planarity of the ligand the structure of the Pt1 complex is distorted. The resultant distortion imposes aerial steric hindrance at the Pt(II)) centre Pt1 which is the reason why the reactivity of Pt1 is about 4–7 times lower than that of the other complexes Pt2 and Pt3. The magnitude of the steric hindrance imposed by the pyridyl bridge cis to the leaving group becomes weaker as the Pt---Pt separation distance increases, leading to the increase in rates of substitution from Pt1 to Pt3 and 4
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Tuning Reactivity of Platinum(II) C
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Declaration This thesis report is b
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Abstract Systematic kinetic and the
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Table of contents Acknowledgements
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2.5.5 Effect of Non-participating G
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5.2.1 Chemical and Solutions ......
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7.2 Experimental Section ..........
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procurements, Messers P. Forder and
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Figure 2.2 Potential energy profile
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Figure 4.6 Concentration dependence
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Figure 6.1 Spectrophotometric titra
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List of Tables Table 2.1 A selectio
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Table 6.4 Summary of rate constants
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TU thiourea DMTU 1,3-dimethyl-2-thi
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Table of Contents-1 Chapter 1 .....
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1.0 Introduction 1.1 Cancer Disease
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toxic potential. The most well-know
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1.3.2.2 Cellular Uptake Cisplatin i
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H 3N OH 2 Pt H 3N OH 2 Active Pt(II
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transformational pathways that comp
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the hydrolysis of the complex, wher
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1.3.4 Terpyridine Platinum(II) Comp
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H 3 N Cl Pt NH 3 H 3 N NH 2 (CH 2 )
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1.4 Kinetic Interest The platinum-b
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3. The effect of varying the positi
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17 R. A. Henderson, The Mechanism o
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Altona J. H. van Boom, G. A. van de
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76 (a)J. Kašpárková, J. Zehnulov
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Table of Contents-2 Chapter Two ...
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List of Tables Table 2.1: A selecti
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The mononuclear Pt(II) complexes 1-
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Potential Energy R + X RX 1 transit
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For the associative mechanism (A),
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the concentration of one of the rea
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k obs , s -1 0.00030 0.00025 0.0002
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k = Ae -Ea/RT 2.14 lnk = lnA - E a
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= 23.76 + R Hence, a plot of ln ⎛
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iii. # Δ V ≈ 10 cm3 mol-1 featur
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conventional methods are classical
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Figure 2.6: Schematic diagram of a
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The light transmitted from the samp
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c. Oxidizability: Ligands that are
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Table 2.1: A selection of n o pt va
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eaction with different nucleophiles
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eaction site from direct attack by
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PEt 3 PEt 3 R PEt 3 Pt Pt Y Y Cl R
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direct displacement of the leaving
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therefore, weaken the bond of the l
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σ-Donation According to classical
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References 1 (a) J. Reedijk, Chem.
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34 R. B. Jordan, Reaction Mechanism
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Table of Contents-3 Chapter 3.The
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Chapter 3 The π-Acceptor Effect in
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In order to extend our understandin
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after which water was added to quen
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O CH 3 + I + N O oH - N O O 7 CH 3
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84% (34.7 mg, 0.0618 mmol). 1 H NMR
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PhCN PhCN Pt Cl Cl + N N CH 3 N CH
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Complex Structure HOMO LUMO PtCl CH
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The geometry-optimised structures i
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against the concentration of the in
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Table 3.2: Summary of the second-or
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constants of CH3PhisoqPtCl decrease
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with π*-orbitals of the ligand. Th
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3.6 References 1 D. Rosenberg, L. V
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30 Microcal TM Origin TM Version 5.
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Figure S3.1: Kinetic trace at 448 n
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ln(k 2 /T) -6.0 -7.5 -9.0 -10.5 -12
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Table S3.3b: Average observed rate
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Table S3.5b: Temperature dependence
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Table S3.8: DFT calculated electros
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List of Figures Figure 4.1: Structu
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Table 4.2: Summary of pKa values fo
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4.1 Introduction Platinum compounds
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cis geometry, leading to dramatic c
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ligand was added to the [{cis-PtCl(
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spectra were measured in and refere
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4.3.1 DFT calculated Optimized Stru
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Table 4.1: A summary of the DFT cal
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H2O-Pt-L-Pt-OH2 H2O-Pt-L-Pt-OH2 H2O
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electrophilicity and acidity of the
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(A) 18 Absorbance 0.08 0.07 0.06 0.
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k obs(3 rd ) , s -1 -5 6.00x10 TMTU
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4.3.4 Kinetics with NMR The substit
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ln([ML] t ) 4.0 3.5 3.0 2.5 2.0 1.5
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ln(k 2(1 st ) /T) -3.5 -4.0 -4.5 -5
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Comple x Table 4.4: Summary of Acti
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The decrease in reactivity of 2,6pz
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Table 4.5: DFT calculated (NBO) cha
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eaction proceeds via bimolecular pa
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References 1 T. Storr, K. H.Thomson
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36 D. Jaganyi, D. Reddy, J.A. Gerte
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Appendix 4 THE INFLUENCE OF THE PYR
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Absorbance at 368. 0 nm 0. 0 8 0. 0
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Table S4.3: Average observed rate c
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k nd obs(2 ) , s-1 0.003 TU DMTU TM
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k obs2 , s -1 2.40x10 -4 2.20x10 -4
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Table S4.13: Average observed rate
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k obs(1 st ) , s -1 0.06 0.04 0.02
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ln(k 2(3 rd ) /T) -10.0 -10.5 -11.0
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SpinWorks 2.5: 2,6 pznClO4 in D2O N
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Table of Contents-5 Chapter 5 .....
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List of Tables Table 5.1: A summary
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5.1 Introduction Multinuclear plati
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onding. For this reason, pKa titrat
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400-300 cm -1): 3308, 3117, 3071 (N
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5.2.6 Spectrophotometric pKa Titrat
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Table 5.1: A summary of DFT-calcula
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However, because the highest occupi
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Table 5.2: Acid dissociation consta
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Table 5.3: A summary of DFT calcula
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H3N 6 eq TU 0 eq TU Ha NH3 Ha Cl TU
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third step due to the trans-effect
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[H 2 O-Pt-(NN)-Pt-OH 2 ] +4 [NU-Pt-
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k obs(1st) / s -1 0.20 TU DMTU TMTU
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thiourea nucleophile is large enoug
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ln(k st 2(1 ) /T) -3 -4 -5 -6 -7 -8
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is the same as the electron-withdra
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associative mode of substitution me
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16 H. Ertürk, J. Maigut, R. Puchta
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43 (a) D. Jaganyi, A. Hofmann and R
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276 nm Absorbance 0 . 6 5 0 . 6 4 0
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k obs(1 st ) , s -1 0.4 0.3 0.2 0.1
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ln(k 2(2 nd ) /T) -8.0 TU -8.5 -9.0
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pzn PPM -1750.0 -1850.0 -1950.0 -20
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Figure S5.13: UV/Visible spectra fo
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k obs(1 st ) in s -1 0.030 0.025 0.
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ln(k 2(2 nd ) /T) -10 -11 -12 -13 -
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9.61 ppm Ha PPM 9.8 9.6 9.4 9.2 9.0
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k obs(3rd) / s -1 -5 8 .00 x 10 T U
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ln(k st 2(1 ) /T) -1.5 TU DMTU TMTU
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ln(k rd 2(3 ) /T) -8.5 -9.0 -9.5 -1
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SpinWorks 2.5: znPt(II)-OP4 in D2O
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Figure S5.31: Mass spectrum for com
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ln(k st 2(1 ) /T) -4 -5 -6 -7 -8 -9
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SpinWorks 2.5: phtPt(II)-OP2 in D2O
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Figure S5.41: Mass spectrum for com
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List of Figures Figure 6.1: Spectro
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Chapter 6 Tuning Reactivity of Plat
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Against this background, several re
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6.2.2 Instruments Microanalyses wer
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Metal Complex Pt3 Yield: 52.5 mg (0
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6.3 Results 6.3.1 Synthesis and Cha
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The pKa values obtained are summari
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Table 6.2: DFT-calculated parameter
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that of dinuclear Pt(II) complexes
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It can be concluded that substituti
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ate constants, kobs(1 st /2 nd ), w
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Table 6.3: Summary of rate constant
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6.3.6 Activation Parameters The act
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pKa1 values become smaller. In addi
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of steric influence is felt by the
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6.5 Conclusion The present study ha
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17 O. F. Wendt and L. I. Elding, 19
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51 Y. Iwadata, K. Kawamura, K. Igar
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Table S6.4(b): Average observed rat
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ln(k 2(2 nd ) /T) -4 -6 -8 -10 -12
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45.0 40 35 30 25 20 %T 15 10 5 0 -5
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k st obs(1 ) in s-1 0.30 Br TU 0.25
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-2304.16 ppm H 3N PPM -2200.0 -2220
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Absorbance 1.6 1.4 1.2 1.0 0.8 0.6
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SH N SH + Mechanism Br N + CO 3 2-
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Figure 7.5: 195Pt NMR spectra of mi
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linker remained coordinated to the
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complexes, have a lower charge and
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ange 326-400 cm -1 (weak) for Pt-Cl
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ButPt, HexPt, OctPt and DecPt, were
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7.3 Results 7.3.1 DFT Calculations
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Structure HOMO LUMO EnPt (C2h) Prop
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Absorbance Table 7.2: Summary of pK
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coordination to the soft Pt(II) cen
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Page 376 and 377: H 3N NH 3 Pt NH 2 OH 2 n NH 3 NH 2
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Page 380 and 381: 7.3.4 Activation Parameters The tem
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Page 386 and 387: References 1 (a) B. Rosenberg, L. V
Page 388 and 389: 32 N. Summa, J. Maigut, R. Puchta a
Page 390 and 391: Appendix 7 Table S7.1: Summary of s
Page 392 and 393: k obs(2 nd ) , in s -1 0.00020 0.00
Page 394 and 395: ln(k 2(2 nd ) /T) -8.5 -9.0 -9.5 -1
Page 396 and 397: k obs(1 st ) , in s -1 0.06 TU DMTU
Page 398 and 399: ln(k 2(1 st ) /T) -3.2 TU DMTU TMTU
Page 400 and 401: Table S7.11: Summary of kobs(2 nd )
Page 402 and 403: Table S7.13: Average observed rate
Page 404 and 405: %T 22.0 20 18 16 14 12 10 8 6 4 2 0
Page 406 and 407: k st obs(1 ) , in s-1 0.10 0.08 0.0
Page 408 and 409: ln(k st 2(1 ) /T) -4.0 TU DMTU TMTU
Page 410 and 411: Figure S7.23: Mass spectra for HexP
Page 412 and 413: Table S21: Average observed rate co
Page 414 and 415: Table S7.23: Summary of kobs(2 nd )
Page 416 and 417: Table S7.25: Average observed rate
Page 418 and 419: 90.0 80 70 60 50 40 30 20 %T 10 0 -
Page 420 and 421: Figure S7.37: Mass spectrum for Hex
Page 422 and 423: Chapter 8 Tuning Reactivity of plat
Page 426 and 427: finally Pt2. The order of reactivit
Page 428: • prolonged survival in the cell
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