Tuning Reactivity of Platinum(II) Complexes

ln([ML] t )
4.0
3.5
3.0
2.5
2.0
1.5
110000 120000 130000 140000 150000 160000 170000 180000
Time (s)
Figure 4.10: First order plot for the reaction of cis-[{PtCl(NH3)2}2-μ-pzn] +2 (0.221 mM)
with excess TU (1.323 mM) (in the molar ratio complex: ligand = 1:6) in
D2O at 30° C, using 1H NMR spectroscopy. The equation used in
calculation is: ln[ML]t = -kobs1 + ln[ML]0, where [ML]0 = [free pyrazine
ligand] = [L]infinite time, and [ML]t = [L]infinite–[L]t using the area of the
signals for released pyrazine ligand.
Looking at Figure 8 & 9, at t = 0, a signal due to the starting complex [{cis–PtCl(NH3)2}2–
μ–pzn](ClO4)2 (δ 195Pt = -2302.2ppm or δ 1 H = 9.04 ppm) is observed. The 1H NMR
spectra shows that after 48 h only two main products had been formed. These are
identified as uncoordinated pyrazine ligand (L), which is expected to appear as a singlet
at δ 1 H = 8.64 ppm, 39,40 and a singlet at δ 195 Pt = -4146.6 ppm 17 corresponding to
Pt(TU)4, which is supported by the 195 Pt NMR spectra. The 1 H and 195 Pt NMR spectra
reveal the formation of intermediate species, [PtCl–L–Pt(TU)] +3, that exhibits two
chemical shifts of Pt(N3Cl) as B at δ 195 Pt = -2962.0 ppm and Pt(N3TU) as C at δ 195 Pt = -
3125.0 ppm (Figure 4.9). Pyrazine (L) protons appear as pairs of doublets at δ 1H = 8.96
as residual coordinated ligand and 8.68 ppm as free ligand seen in Figure 4.8. 39,40 Thus,
the coordinated aqua molecules are sequentially substituted from Pt(II) centres in the
first two steps. The 195 Pt NMR signals at -3125.0 ppm (marked as C) and -3276.0 ppm
(marked as D) in Figure 4.9, are both typical of PtN3S coordinating sphere 41 and -4146.6
24