Tuning Reactivity of Platinum(II) Complexes

It can be concluded that substitution of the aqua ligands at each of Pt(II) centres occurs
simultaneously in all the complexes investigated irrespective of the nature of the spacer
group. This is consistent with the symmetrical nature of the complexes. But, the second
and slower subsequent step is due to the strong labilising thiourea and other
nucleophiles inducing dissociation of the linker. The second step also is sensitive to
variations in the nature and size of spacer group of the pyridyl moiety. Thus, the overall
substitution process can be represented by the reaction shown in Scheme 6.3.
Y
H Pt N
2O N Pt H2O Y
NU Pt N N Pt NU 2Pt(NU)
4
4+
NU Pt N N Pt NU
Y
N N = free ligand: N S N , N S S N ,
N CH CH 2 2 N
NU = TU, DMTU, TMTU, SCN - , I - , Br -
Br - only realised k 1
k 1 /NU -n
-2H 2 O
(2n + 4)+
k2 /NU-n 17
(4n+2)+
+
Y
N
Y
N
(2n + 4)+
Scheme 6.3: Substitution Mechanism for the reaction between the S, S–S and C–C
dinuclear Pt(II) complexes with selected nucleophiles.
In all cases, the first step was fast and was therefore studied on the stopped-flow
reaction analyzer whereas the subsequent slower step was studied by the UV-Vis
spectroscopic method. The general course of the substitution reactions for 1.0 mM Pt2
with 3.0 mM TU are recorded in Scheme 6.4.