Synthesis, Structure, and Photophysical Properties of Platinum(II) (N,C,N′) Pincer Complexes Derived from Purine Nucleobases

Abstract

The synthesis of a series of Pt{κ 3 -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 the N,C-cyclometalated fragment, whereas an amine, imine, or pyridine substituent of the phenyl ring supplies the additional N′-coordination point to the pincer complex. The purine N,C-fragment has two coordination positions with the metal (N1 and N7), but the formation of the platinum complexes is totally regioselective. Coordination through the N7 position leads to the thermodynamically favored [6.5]-Pt{κ 3 -N7,C,N′-[L]}X complexes. However, the coordination through the N1 position is preferred by the amino derivatives, leading to the isomeric kinetic [5.5]-Pt{κ 3 -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 CH 2 Cl 2 solution 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.

Organometallic modification confers oligonucleotides new functionalities

“…Interesting properties of organometallic modifications as labels are not limited to redox chemistry, as exemplified by the recent report on oligonucleotides bearing phosphorescent platinacyclic chelates. Many more studies have been published on related nucleoside, nucleotide and dinucleotide analogues, 171,197–199 predicting this to be an active field in the coming years. The atomic weights and isotope distributions of many metals forming stable organometallic complexes, notably mercury and the platinum group metals, are very distinct from those of the biogenic elements, possibly allowing laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) or nanoscale secondary ion mass spectrometry (NanoSIMS) imaging of correspondingly modified oligonucleotides.…”

N,C,N-Pincers in Platinum Bimetallic Complexes: Influence of the Pincer and Bridging Ligands on the Metal–Metal Bond and the Photophysical Properties

“…The N,C,N -ligands occupy a prominent position among the pincers . In particular, those generated by the activation of the C–H bond at the 2-position of the central ring of 1,3-di­(2-pyridyl)­benzene-type pro-ligands and related molecules attract increasing interest in platinum­(II) chemistry . In this context, we have recently studied the conflict posed by the joint coordination, to platinum­(II), of ligands such as 1,3-bis­(2-pyridyl)-4,6-dimethylphenyl- or 1,3-bis­(2-pyridyloxy)­phenyl and chelating groups of the type 3-(2-pyridyl)-pyrazolate, seeking to analyze the influence of typical parameters of pincer ligands, including bite angle, hemilability, and electron delocalization capacity, on the emissive properties of the resulting metals species.…”