Tuning Reactivity of Platinum(II) Complexes
Tuning Reactivity of Platinum(II) Complexes Tuning Reactivity of Platinum(II) Complexes
Metal Complex Pt3 Yield: 52.5 mg (0. 058 mmol, 65.0 %). 1H NMR (500.5 MHz, D2O) δ/ppm: 8.96 (d, 4H of py in bpe); 7.78 (d, 4H of py in bpe); 3.66 (s, 4H for 2CH2 of bpe). 195 Pt NMR (107.5 MHz, D2O) δ/ ppm: -2284.66. IR (KBr, 400-300 cm -1): 3285 (N–H stretch); 1621 (C=N/C=C, pyridine ring stretch), 1436 (m, bpe), 1340 (vw, bpe), 1212 (w, bpe); 1090-1100 (perchlorate counter ion); 556 (Pt–N stretch). TOF MS/ES +. (m/z, M 2+): 356.535 (C12H22N6Pt2Cl2, species). Anal. Calcd for C12H24N6Cl4O8Pt2: H, 2.65; C, 27.64; N, 9.21. Found: H, 2.59; C, 27.69; N, 9.71%. 6.2.5 Preparation of the Dinuclear Pt(II) Diaqua Complexes The chloro complexes (Pt1 to Pt3) were converted into aqua analogues using literature procedure. 40 The resultant aqua solutions were brought to a final complex concentration of 4.41 x 10 -4 , 4.43 x 10 -4 and 1.13 x 10 -4 M for [{cis–PtOH2(NH3)2}2–μ–dps](ClO4)2 (Pt1), [{cis–Pt(OH2)(NH3)2}2–μ–dpds](ClO4)2 (Pt2), [{cis–Pt(OH2)(NH3)2}2–μ– bpe](ClO4)2 (Pt3), respectively. The solution was acidified with HClO4 to pH 1.0 (for determination of pKa values) and pH 2.0 (for kinetic measurements). The ionic strength was adjusted to 0.10 M with NaClO4. 6.2.6 Preparation of Kinetic Solutions The kinetic measurements were studied in 0.10 M NaClO4, at pH ca. 2.0, since the perchlorate ions do not coordinate to Pt(II) in aqueous solution, and in order to prevent deprotonation of the aqua ligand. 20(b) Nucleophile solutions of different concentrations, viz. 20, 40, 60, 80 and 100-fold excess of appropriate metal complex concentration were prepared shortly before use by quantitative dilution of the corresponding stock solution using the 0.10 M (NaClO4, adjusted with HClO4 to pH 2.0). 41 This was to maintain the reaction under pseudo first-order conditions and drive the reaction to completion. 6.2.7 Spectrophotometric pKa Titrations The pH of the aqueous solutions was measured using a Jenway 4330 Conductivity/pH meter equipped with a Micro 4.5 diameter glass electrode after calibration with standard buffers pH 4.0, 7.0 and 10.0 at 25 °C. The pH electrode was filled with 3M NaCl electrolyte to prevent precipitation of KClO4 during use. In order to avoid absorbance 7
corrections due to dilution, a large volume (200ml) of each of the complex solutions was used during the titrations. Spectrophotometric pH titrations were carried out using NaOH as the base. Subsequent pH changes were obtained by stepwise additions of crushed solid NaOH pellets in the pH range 2-3, micropipette dropwise addition of saturated, 1.0 and 0.1 M NaOH or conc. HClO4 (for reversibility of the pH) to the bulk of the complex solution, prior to withdrawal of 2 ml aliquots of the solution. After each of the measurements, the aliquots were not returned to the sample solutions to avoid in situ contamination by chloride ions from the pH electrode. 6.2.8 Computational Details The geometries of all the complexes in aqua-form with total charges of +4 were optimized, in vacuo, using Density functional Theory (DFT) utilizing the B3LYP, 42 a three parameter hybrid functional method, and the LACVP** (Los Alamos Core Valence Potentials) 43 pseudo-potentials basis set as implemented in Spartan `04 for Windows ® program. B3LYP relates to Becke’s three parameter hybrid functional 42 that has been proven to be superior to traditional functionals. The mononuclear complex, cis- [Pt(H2O)(NH3)2(4-methylpyridine)] +2 , Pt4, is included for comparative purposes with respect to the pKa and DFT results of Pt3 6.2.9 Kinetic Measurements Spectral changes resulting from mixing separately each of the complexes Pt1, Pt2, and Pt3 with ligand solutions were recorded over the wavelength range 200-600 nm to establish a suitable wavelength at which the kinetic measurement would be performed on a Varian Cary 100 Bio spectrophotometer. The kinetics of the lability of coordinated water was followed spectrophotometrically by monitoring the change in absorbance at suitable wavelengths. The wavelength values are given as supplementary information in Table S6.1 (Appendix 6). 8
- Page 256 and 257: k obs(1 st ) , s -1 0.4 0.3 0.2 0.1
- Page 258 and 259: Table S5.5: Average observed rate c
- Page 260 and 261: ln(k 2(2 nd ) /T) -8.0 TU -8.5 -9.0
- Page 262 and 263: pzn PPM -1750.0 -1850.0 -1950.0 -20
- Page 264 and 265: Table S5.9: Average observed rate c
- Page 266 and 267: Figure S5.13: UV/Visible spectra fo
- Page 268 and 269: k obs(1 st ) in s -1 0.030 0.025 0.
- Page 270 and 271: Table S5.17: Average observed rate
- Page 272 and 273: ln(k 2(2 nd ) /T) -10 -11 -12 -13 -
- Page 274 and 275: 9.61 ppm Ha PPM 9.8 9.6 9.4 9.2 9.0
- Page 276 and 277: Table S5.22: Average observed rate
- Page 278 and 279: k obs(3rd) / s -1 -5 8 .00 x 10 T U
- Page 280 and 281: ln(k st 2(1 ) /T) -1.5 TU DMTU TMTU
- Page 282 and 283: ln(k rd 2(3 ) /T) -8.5 -9.0 -9.5 -1
- Page 284 and 285: SpinWorks 2.5: znPt(II)-OP4 in D2O
- Page 286 and 287: Figure S5.31: Mass spectrum for com
- Page 288 and 289: Table S5.28: Average observed rate
- Page 290 and 291: Table S5.29: Average observed rate
- Page 292 and 293: ln(k st 2(1 ) /T) -4 -5 -6 -7 -8 -9
- Page 294 and 295: SpinWorks 2.5: phtPt(II)-OP2 in D2O
- Page 296 and 297: Figure S5.41: Mass spectrum for com
- Page 298 and 299: List of Figures Figure 6.1: Spectro
- Page 300 and 301: Chapter 6 Tuning Reactivity of Plat
- Page 302 and 303: Against this background, several re
- Page 304 and 305: 6.2.2 Instruments Microanalyses wer
- Page 308 and 309: 6.3 Results 6.3.1 Synthesis and Cha
- Page 310 and 311: The pKa values obtained are summari
- Page 312 and 313: Table 6.2: DFT-calculated parameter
- Page 314 and 315: that of dinuclear Pt(II) complexes
- Page 316 and 317: It can be concluded that substituti
- Page 318 and 319: ate constants, kobs(1 st /2 nd ), w
- Page 320 and 321: Table 6.3: Summary of rate constant
- Page 322 and 323: 6.3.6 Activation Parameters The act
- Page 324 and 325: pKa1 values become smaller. In addi
- Page 326 and 327: of steric influence is felt by the
- Page 328 and 329: 6.5 Conclusion The present study ha
- Page 330 and 331: 17 O. F. Wendt and L. I. Elding, 19
- Page 332 and 333: 51 Y. Iwadata, K. Kawamura, K. Igar
- Page 334 and 335: Table S6.3: Average observed rate c
- Page 336 and 337: Table S6.4(b): Average observed rat
- Page 338 and 339: ln(k 2(2 nd ) /T) -4 -6 -8 -10 -12
- Page 340 and 341: 45.0 40 35 30 25 20 %T 15 10 5 0 -5
- Page 342 and 343: k st obs(1 ) in s-1 0.30 Br TU 0.25
- Page 344 and 345: Table S6.9: Average observed rate c
- Page 346 and 347: -2304.16 ppm H 3N PPM -2200.0 -2220
- Page 348 and 349: Table S6.10: Average observed rate
- Page 350 and 351: Table S6.13: Average observed rate
- Page 352 and 353: Absorbance 1.6 1.4 1.2 1.0 0.8 0.6
- Page 354 and 355: SH N SH + Mechanism Br N + CO 3 2-
Metal Complex Pt3<br />
Yield: 52.5 mg (0. 058 mmol, 65.0 %). 1H NMR (500.5 MHz, D2O) δ/ppm: 8.96 (d, 4H <strong>of</strong><br />
py in bpe); 7.78 (d, 4H <strong>of</strong> py in bpe); 3.66 (s, 4H for 2CH2 <strong>of</strong> bpe). 195 Pt NMR (107.5 MHz,<br />
D2O) δ/ ppm: -2284.66. IR (KBr, 400-300 cm -1): 3285 (N–H stretch); 1621 (C=N/C=C,<br />
pyridine ring stretch), 1436 (m, bpe), 1340 (vw, bpe), 1212 (w, bpe); 1090-1100<br />
(perchlorate counter ion); 556 (Pt–N stretch). TOF MS/ES +. (m/z, M 2+): 356.535<br />
(C12H22N6Pt2Cl2, species). Anal. Calcd for C12H24N6Cl4O8Pt2: H, 2.65; C, 27.64; N, 9.21.<br />
Found: H, 2.59; C, 27.69; N, 9.71%.<br />
6.2.5 Preparation <strong>of</strong> the Dinuclear Pt(<strong>II</strong>) Diaqua <strong>Complexes</strong><br />
The chloro complexes (Pt1 to Pt3) were converted into aqua analogues using literature<br />
procedure. 40 The resultant aqua solutions were brought to a final complex concentration<br />
<strong>of</strong> 4.41 x 10 -4 , 4.43 x 10 -4 and 1.13 x 10 -4 M for [{cis–PtOH2(NH3)2}2–μ–dps](ClO4)2<br />
(Pt1), [{cis–Pt(OH2)(NH3)2}2–μ–dpds](ClO4)2 (Pt2), [{cis–Pt(OH2)(NH3)2}2–μ–<br />
bpe](ClO4)2 (Pt3), respectively. The solution was acidified with HClO4 to pH 1.0 (for<br />
determination <strong>of</strong> pKa values) and pH 2.0 (for kinetic measurements). The ionic strength<br />
was adjusted to 0.10 M with NaClO4.<br />
6.2.6 Preparation <strong>of</strong> Kinetic Solutions<br />
The kinetic measurements were studied in 0.10 M NaClO4, at pH ca. 2.0, since the<br />
perchlorate ions do not coordinate to Pt(<strong>II</strong>) in aqueous solution, and in order to prevent<br />
deprotonation <strong>of</strong> the aqua ligand. 20(b) Nucleophile solutions <strong>of</strong> different concentrations,<br />
viz. 20, 40, 60, 80 and 100-fold excess <strong>of</strong> appropriate metal complex concentration were<br />
prepared shortly before use by quantitative dilution <strong>of</strong> the corresponding stock solution<br />
using the 0.10 M (NaClO4, adjusted with HClO4 to pH 2.0). 41 This was to maintain the<br />
reaction under pseudo first-order conditions and drive the reaction to completion.<br />
6.2.7 Spectrophotometric pKa Titrations<br />
The pH <strong>of</strong> the aqueous solutions was measured using a Jenway 4330 Conductivity/pH<br />
meter equipped with a Micro 4.5 diameter glass electrode after calibration with<br />
standard buffers pH 4.0, 7.0 and 10.0 at 25 °C. The pH electrode was filled with 3M NaCl<br />
electrolyte to prevent precipitation <strong>of</strong> KClO4 during use. In order to avoid absorbance<br />
7