Monomeric Ti(IV)-based complexes incorporating luminescent nitrogen ligands: synthesis, structural characterization, emission spectroscopy and cytotoxic activities

This manuscript describes the synthesis of a series of neutral titanium(IV) monomeric complexes constructed around a TiO4N2 core. The two nitrogen atoms that compose the coordination sphere of the metallic center belong to 2,2′-bipyrimidine ligands homo-disubstituted in the 4 and 4′ positions by methyl (2a), phenylvinyl (2b), naphthylvinyl (2c) or anthrylvinyl (2d) groups. The crystal structures of these complexes named [Ti(1)2(2a)], [Ti(1)2(2b)], [Ti(1)2(2c)] and [Ti(1)2(2d)] (where 1 is a 2,2′-biphenolato ligand substituted in the 6 and 6′ positions by phenyl groups) are reported. The hydrolytic stability of the four complexes is evaluated by monitoring the evolution of the free 2a–d signals by 1H NMR spectroscopy. For the conditions tested (6 mM, DMSO-d6/D2O: 8/1), a rather good stability with t1/2 ranging from 180 to 300 min is determined for the complexes. In the presence of an acid (DCl), the hydrolysis of [Ti(1)2(2a)] is faster than without an acid. The cytotoxic activity against gastric cancer cells of the titanium-based compounds and the free disubstituted 2,2′-bipyrimidine ligands is tested, showing IC50 ranging from 6.2 ± 1.2 μM to 274 ± 56 μM. The fluorescence studies of the ligands 2a–d, and the complexes [Ti(1)2(2a–d)] reveal an important fluorescence loss of the ligands 2c and 2d upon coordination with the Ti(1)2 fragment. Frontier orbitals obtained by DFT calculations permit us to explain this fluorescence quenching.Other supports : Centre National pour la Recherche Scientifique (CNRS, France), ARC, Ligue contre le Cancer, European action COST CM1105 (C. G.

Modified pyridine–triazole and 2,2′-bipyrimidine ligands generating robust titanium complexes constructed around a TiO4N2 core

International audienceThe synthesis and characterization of novel chelate nitrogen ligands with phasmidic tails (pyridine-triazole ligand 1b; 2,2'bipyrimidine ligands 2b and 3b) is reported, as well as their titanium (IV) coordination complexes. The analogous ligands 1a, 2a and 3a with methoxy substituents instead of the tails were also synthesized, together with titanium complexes that could be crystallographically characterized. A good agreement is noticed between analytical data of the complexes in solution (NMR) and in the solid state (X-ray diffraction). The complexes are overall stable on phases like alumina or silica, so that they could be characterized by TLC and sometimes chromatographied. Supramolecular architectures were generated from an equimolar solution of titanium (IV) isopropoxide, ligand 1a and a polyphenol ligand 5-H4, leading to a double-stranded helicate characterized by MS, NMR and crystallography, which was then converted into a trinuclear complex as shown by MS and NMR DOSY data. The liquid-crystalline behaviour of the ligands 1b, 2b and 3b incorporating the long alkyl tails, and of the complexes derived from these ligands, has been investigated