Tuning Reactivity of Platinum(II) Complexes

coordination of sulphur nucleophiles. 21 Vasak et al. 22 have also shown that whereas all
ligands in cis-Pt(II)-based compounds were replaced by cysteine and thiolates, trans-
Pt(II)-compounds retained their N-donor ligands; thereby remaining in a potentially
active form. Factors that mediate these reaction processes remain least understood. It
would, therefore, be interesting and useful to study the kinetics of the pyrazine-bridged
dinuclear Pt(II) complexes with a common cis geometry, to understand the mode of in
vivo activities of these complexes with sulphur-donor ligands.
To gain further insight into the influence of the rigid bridging ligand on the reactivity of
the platinum(II) centres in dinuclear complexes, a series of bridged dinuclear
platinum(II) complexes of the type, [cis-{Pt(H2O)(NH3)2}2-µ-pzn] 4+ (where pzn =
pyrazine), was investigated structures of the complexes are given in Figure 4.1).
NH 3
NH 3
OH 2
Pt
NH 3
OH 2
Pt
NH 3
N N Pt
NH 3
OH 2
N N Pt
NH 3
NH 3
N N Pt
expected to change. This would affect the basicity of the whole complex, especially in the
3
OH 2
Pt
NH 3
pzn 2,3 pzn
2,5 pzn
NH 3
OH 2
NH 3
+4 +4
+4
NH 3
OH 2
Pt
1
NH 3
3
4
N N Pt
8
5
6
2,6 pzn
Figure 4.1: Structures of the investigated dinuclear Pt(II) complexes. The numbering
7
NH 3
OH 2
NH 3
2
OH 2
scheme employed for pKa1 and pKa2, the NBO charges, bond length and bond
NH 3
NH 3
angles for the complexes is shown on the structure of 2,6pzn.
Isomeric dimethylpyrazine bridging ligands were used in this study because by varying
the position of the methyl groups on the pyrazine ring, the basic strength and σ-donor
properties of the tertiary amine (sp 2) N-atom coordinated to the Pt(II) centre is
+4