Aqua substitution from mononuclear Pt(II) complexes with 2-(pyrazol-1-ylmethyl)quinoline non-leaving ligands
Creators: name: Bongumusa B. Khusi
name: Mambanda, Allen
name: Deogratius Jaganyi
Publisher: name: Taylor & Francis
Year: 2016
Subjects: subject: Biophysics
subject: Biochemistry
subject: 29999 Physical Sciences not elsewhere classified
subject: FOS: Physical sciences
subject: FOS: Physical sciences
subject: Medicine
subject: Microbiology
subject: FOS: Biological sciences
subject: FOS: Biological sciences
subject: Genetics
subject: Molecular Biology
subject: Neuroscience
subject: Evolutionary Biology
subject: 39999 Chemical Sciences not elsewhere classified
subject: FOS: Chemical sciences
subject: FOS: Chemical sciences
subject: Sociology
subject: FOS: Sociology
subject: FOS: Sociology
subject: Immunology
subject: FOS: Clinical medicine
subject: FOS: Clinical medicine
subject: Developmental Biology
subject: Cancer
subject: 111714 Mental Health
subject: FOS: Health sciences
subject: FOS: Health sciences
subject: 110309 Infectious Diseases
subject: Computational Biology

description: The rates of aqua substitution from [Pt{2-(pyrazol-1-ylmethyl)quinoline}(H<sub>2</sub>O)<sub>2</sub>](ClO<sub>4</sub>)<sub>2</sub>, [<b>Pt(H</b><sub><b>2</b></sub><b>Qn)</b>], [Pt{2-(3,5-dimethylpyrazol-1-ylmethyl)quinoline}(H<sub>2</sub>O)<sub>2</sub>](ClO<sub>4</sub>)<sub>2</sub>, [<b>Pt(dCH</b><sub><b>3</b></sub><b>Qn)</b>], [Pt{2-[(3,5-bis(trifluoromethyl)pyrazol-1-ylmethyl]quinoline}(H<sub>2</sub>O)<sub>2</sub>](ClO<sub>4</sub>)<sub>2</sub>, [<b>Pt(dCF</b><sub><b>3</b></sub><b>Qn)</b>], and [Pt{2-[(3,5-bis(trifluoromethyl)pyrazol-1-ylmethyl]pyridine}(H<sub>2</sub>O)<sub>2</sub>](ClO<sub>4</sub>)<sub>2</sub>, <b>[Pt(dCF</b><sub><b>3</b></sub><b>Py)]</b>, with three sulfur donor nucleophiles were studied. The reactions were followed under <i>pseudo</i><i>-</i>first-order conditions as a function of nucleophile concentration and temperature using a stopped-flow analyzer and UV/visible spectrophotometry. The substitution reactions proceeded sequentially. The second-order rate constants for substituting the aqua ligands in the first substitution step increased in the order <b>Pt(dCH</b><sub><b>3</b></sub><b>Qn)</b> Pt(dCF<sub><b>3</b></sub><b>Qn)</b> Pt(H<sub><b>2</b></sub><b>Qn)</b> Pt(dCF<sub><b>3</b></sub><b>Py)</b>, while that of the second substitution step was <b>Pt(dCH</b><sub><b>3</b></sub><b>Qn)</b> Pt(dCF<sub><b>3</b></sub><b>Qn)</b> Pt(dCF<sub><b>3</b></sub><b>Py)</b> Pt(H<sub><b>2</b></sub><b>Qn)</b>. The reactivity trends confirm that the quinoline substructure in the (pyrazolylmethyl)quinoline ligands acts as an apparent donor of electron density toward the metal center rather than being a <i>π</i>-acceptor. Measured p<i>K</i><sub>a</sub> values from spectrophotometric acid–base titrations were <b>Pt(H</b><sub><b>2</b></sub><b>Qn)</b> (p<i>K</i><sub>a1</sub> = 4.56; p<i>K</i><sub>a2</sub> = 6.32), <b>Pt(dCH</b><sub><b>3</b></sub><b>Qn)</b> (p<i>K</i><sub>a1</sub> = 4.88; p<i>K</i><sub>a2</sub> = 6.31), <b>Pt(dCF</b><sub><b>3</b></sub><b>Qn)</b> (p<i>K</i><sub>a1</sub> = 4.07; p<i>K</i><sub>a2</sub> = 6.35), and <b>Pt(dCF</b><sub><b>3</b></sub><b>Py)</b> (p<i>K</i><sub>a1</sub> = 4.76; p<i>K</i><sub>a2</sub> = 6.27). The activation parameters from the temperature dependence of the second-order rate constants support an associative mechanism of substitution.