The synthesis of
a series of Pt{κ3-N,C,N′-[L]}X
(X = Cl, RC≡C) pincer complexes derived from purine and purine
nucleosides is reported. In these complexes, the 6-phenylpurine skeleton
provides theN,C-cyclometalated
fragment, whereas an amine, imine, or pyridine substituent of the
phenyl ring supplies the additionalN′-coordination
point to the pincer complex. The purineN,C-fragment has two coordination positions with the metal
(N1 andN7), but the formation of
the platinum complexes is totally regioselective. Coordination through
theN7 position leads to the thermodynamically favored
[6.5]-Pt{κ3-N7,C,N′-[L]}X complexes. However, the coordination
through theN1 position is preferred by the amino
derivatives, leading to the isomeric kinetic [5.5]-Pt{κ3-N1,C,N′-[L]}X complexes. Extension of the reported methodology to
complexes having both pincer and acetylide ligands derived from nucleosides
allows the preparation of novel heteroleptic bis-nucleoside compounds
that could be regarded as organometallic models of Pt-induced interstrand
cross-link. Complexes having amine or pyridine arms are green phosphorescence
emitters upon photoexcitation at low concentrations in CH2Cl2solution and in poly(methyl methacrylate) (PMMA) films.
They undergo self-quenching at high concentrations due to molecular
aggregation. The presence of intermolecular π–π
stacking and weak Pt···Pt interactions was also observed
in the solid state by X-ray diffraction analysis.