Tuning Reactivity of Platinum(II) Complexes

[H 2 O-Pt-(NN)-Pt-OH 2 ] +4
[NU-Pt-(NN)-Pt-NU] +4
k 2(1 st )
+NU
-H 2 O
k 2(3 rd )
+2NU
[H 2 O-Pt-(NN)-Pt-NU] +4
where, (NN) = pzn, pmn, pdn, qzn, pht bridging ligand
NU = nucleophile
2 [(NU) 4 Pt] +2 + (NN)
22
k 2(2 nd )
+NU
-H2O [NU-Pt-(NN)-Pt-NU] +4
Scheme 5.4: Suggested Substitution Mechanism for the Dinuclear Pt(II) complex system
with Thiourea and its substituted derivatives.
The observed pseudo first order rate constants, kobs, as a function of total concentration
of nucleophile are shown in Figures 5.6, 5.7 and 5.8 for pmn complex (0.17 mM) with
the TU, DMTU and TMTU, and can be described by equation 1.
kobs(1 st /2 nd /3 rd) = k2( 1 st /2 nd /3 rd) [NU] (1)
The plots show that all the kobs linearly depend on concentration of the entering
nucleophile with zero intercepts, an indication that there was little or no reverse
reaction. The values of the observed rate constants, kobs, used in determining k2(1 st ) were
an average of five to seven independent runs obtained from the stopped-flow; while an
average of multiple readings obtained from the UV-Vis spectrophotometer were used
for the second and third steps. The second-order rate constants, k2(i), for the first,
second and third steps for all the reactions were obtained from the slope of plots of kobs
vs. [NU], using Origin 7.5 ®37 program. The values of the second order rate constants are
summarized in Table 5.4.