Tuning Reactivity of Platinum(II) Complexes
Tuning Reactivity of Platinum(II) Complexes Tuning Reactivity of Platinum(II) Complexes
cis geometry, leading to dramatic changes in the substitution of the aqua ligands. At the same time, the bulky methyl substituents would introduce steric hindrance on the cis- Pt(II) centre. Therefore, the variation of the substituents on the pyrazine-bridge enabled a systematic study of the thermodynamic (pKa, where coordinated water was deprotonated) and kinetic properties of the Pt(II) centres. 4.2 Experimental 4.2.1 Chemicals and Reagents Pyrazine (99%), 2,3-dimethylpyrazine (99%), 2,5-dimethylpyrazine (99%), 2,6- dimethylpyrazine (99%), † NaClO4.H2O (98%), and HClO4 (70%) were obtained from Aldrich and were used without further purification. AgClO4 (99.98%, Aldrich) was stored under nitrogen and used as supplied. Cis-(PtCl2(NH3)2 (99%) was purchased from Strem chemicals. The nucleophiles §thiourea (TU, 99%), N,N-dimethyl-2-thiourea (DMTU, 99%), N,N,N,N-tetramethyl-2-thiourea (TMTU, 98%) used in the kinetic measurements were obtained from Aldrich. Stock solutions of the nucleophiles were prepared, shortly before use, by dissolving known amounts of the nucleophiles in 0.1M NaClO4/HClO4 aqueous solution of constant ionic strength. Since it is well-known that the perchlorate ion, (ClO4 -), does not coordinate to Pt(II), 23 its presence in aqueous solution would not interfere with the kinetic measurements. Ultrapure water (Modulab Systems) was used in all experiments. All other reagents were of analytical grade quality and were used without further purification. Caution! †Perchloric acid and salts are potentially explosive, particularly at high temperatures and must be handled with caution and in small amounts. §Thiourea and its substituted derivatives are suspected carcinogens and the necessary safety measures must be adhered to when handling these reagents. 4
4.2.2 Synthesis of compounds A total of four dinuclear Pt(II) complexes, namely [cis-{PtCl(NH3)2}2-μ-pzn](ClO4)2 (pzn) (pzn = pyrazine), [cis-{PtCl(NH3)2}2-μ-2,3 pzn](ClO4)2 (2,3pzn) (2,3pzn = 2,3- dimethylpyrazine), [cis-{PtCl(NH3)2}2-μ-2,5pzn](ClO4)2 (2,5pzn) (2,5pzn = 2,5- dimethylpyrazine), and [cis-{PtCl(NH3)2}2-μ-2,6pzn]Cl2 (2,6pzn) (2,6pzn = 2,6- dimethylpyrazine) were synthesized starting from the precursor compound [cis- {PtCl(NH3)2(DMF)}]ClO4 using AgClO4 following the procedure reported in literature. 24, 25 4.2.3 Preparation of platinum complexes cis-[{PtCl(NH3)2}2–μ–pzn](ClO4)2(pzn) The cis-[{PtCl(NH3)2}2-μ-pzn](ClO4)2 (pzn) was prepared following a modified procedure to that used previously for similar compounds as illustrated in Scheme 4.1. 26 NH 3 NH 3 NH 3 Cl Pt Cl + Cl NH 3 AgClO 4 N N Pt Pt NH 3 where, NH 3 DMF, 50 o C Cl (ClO 4 ) 2 N N = N N N N [Pt(NH 3 ) 2 (DMF)Cl]ClO 4 C H 3 C H 3 N N N N the dark (78.2 mg, 0.976 mmol) of pyrazine ligand (pzn) at room temperature. The 5 DMF 40-50 o C C H 3 0.5 mol + AgCl (s) CH 3 C H 3 N N pzn 2,6-pzn 2,5-pzn 2,3-pzn Scheme 4.1 Synthetic route for the complexes pzn, 2,3pzn, 2,5pzn and 2,6pzn To 50 ml of stirred solution of (1.039 mmol) [{cis-PtCl (NH3)2(DMF)]ClO4 was added in CH 3
- Page 100 and 101: References 1 (a) J. Reedijk, Chem.
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- Page 114 and 115: 84% (34.7 mg, 0.0618 mmol). 1 H NMR
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- Page 118 and 119: Complex Structure HOMO LUMO PtCl CH
- Page 120 and 121: The geometry-optimised structures i
- Page 122 and 123: against the concentration of the in
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- Page 126 and 127: constants of CH3PhisoqPtCl decrease
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- Page 130 and 131: 3.6 References 1 D. Rosenberg, L. V
- Page 132 and 133: 30 Microcal TM Origin TM Version 5.
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4.2.2 Synthesis <strong>of</strong> compounds<br />
A total <strong>of</strong> four dinuclear Pt(<strong>II</strong>) complexes, namely [cis-{PtCl(NH3)2}2-μ-pzn](ClO4)2 (pzn)<br />
(pzn = pyrazine), [cis-{PtCl(NH3)2}2-μ-2,3 pzn](ClO4)2 (2,3pzn) (2,3pzn = 2,3-<br />
dimethylpyrazine), [cis-{PtCl(NH3)2}2-μ-2,5pzn](ClO4)2 (2,5pzn) (2,5pzn = 2,5-<br />
dimethylpyrazine), and [cis-{PtCl(NH3)2}2-μ-2,6pzn]Cl2 (2,6pzn) (2,6pzn = 2,6-<br />
dimethylpyrazine) were synthesized starting from the precursor compound [cis-<br />
{PtCl(NH3)2(DMF)}]ClO4 using AgClO4 following the procedure reported in literature. 24,<br />
25<br />
4.2.3 Preparation <strong>of</strong> platinum complexes<br />
cis-[{PtCl(NH3)2}2–μ–pzn](ClO4)2(pzn)<br />
The cis-[{PtCl(NH3)2}2-μ-pzn](ClO4)2 (pzn) was prepared following a modified<br />
procedure to that used previously for similar compounds as illustrated in Scheme 4.1. 26<br />
NH 3<br />
NH 3<br />
NH 3<br />
Cl<br />
Pt<br />
Cl<br />
+<br />
Cl<br />
NH 3<br />
AgClO 4<br />
N N Pt<br />
Pt NH 3<br />
where,<br />
NH 3<br />
DMF, 50 o C<br />
Cl<br />
(ClO 4 ) 2<br />
N N = N N N N<br />
[Pt(NH 3 ) 2 (DMF)Cl]ClO 4<br />
C<br />
H 3<br />
C<br />
H 3<br />
N N<br />
N N<br />
the dark (78.2 mg, 0.976 mmol) <strong>of</strong> pyrazine ligand (pzn) at room temperature. The<br />
5<br />
DMF<br />
40-50 o C<br />
C<br />
H 3<br />
0.5 mol<br />
+ AgCl (s)<br />
CH 3<br />
C<br />
H 3<br />
N N<br />
pzn 2,6-pzn 2,5-pzn 2,3-pzn<br />
Scheme 4.1 Synthetic route for the complexes pzn, 2,3pzn, 2,5pzn and 2,6pzn<br />
To 50 ml <strong>of</strong> stirred solution <strong>of</strong> (1.039 mmol) [{cis-PtCl (NH3)2(DMF)]ClO4 was added in<br />
CH 3
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