Tuning Reactivity of Platinum(II) Complexes

H 3N
NH 3
Pt NH 2
OH 2
n
NH 3
NH 2 Pt NH 3
OH 2
4+
where
n = 0, 1, 2, 4, 6, 8
k 2,1
NU = TU, DMTU, TMTU
H3N NU
-2H2O
NH 3
Pt NH 2
NU
NU
20
NU
n
NH 3
NH 2 Pt NH 3
H Pt NH 3N 2 n
NH Pt NH
2 3
NU
Scheme 7.4: Proposed mechanism of aqua substitution from the investigated complexes
k 2,2
by a series of thiourea nucleophiles (NU)
Typical kinetic traces recorded by mixing solutions of OctPt (5.285 × 10 −5 M) and TU
(1.664 × 10 −3 M) in the stopped-flow instrument or UV/Vis spectrophotometer, at an
ionic strength of 0.1 M (NaClO4), are shown in Figure 7.6. All the kinetic traces were
described by single exponential functions. The obtained pseudo first-order rate
constants, kobs, were found to be directly proportional to the concentration of the S-
donor nucleophile. Typical plots for the reactions of OctPt with the S-donor nucleophiles
at different concentrations are shown in Figures 7.7 & 7.8 (also Figures S7.1-S7.2, S7.6-
S7.7, S7.11-S7.12, S7.17-S7.18 and S7.26-S7.27 for the corresponding complexes
EnPt, PropPt, ButPt, HexPt and DecPt, Appendix 7). The second-order rate constant,
k2, for the forward reaction of each complex with a particular nucleophile was calculated
from the slope of a plot of the observed rate constant, kobs, versus the nucleophile
concentration using Origin 7.5 ® . 38 The plots obtained can be described by Equation (1).
The absence of an intercept indicates a direct ligand-exchange of aqua or ammine ligand
for thiourea nucleophile and shows that the nucleophilicity of these sulphur donors is
strong enough to suppress the kinetic influence from the solvent path.
kobs1 st /2 nd = k2,1 st/2,2 nd [NU] (1)
NU
NU
NU
4+
4+