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

Abstract

This manuscript describes the synthesis of a series of neutral titanium(iv) monomeric complexes constructed around a TiON 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)(2a)], [Ti(1)(2b)], [Ti(1)(2c)] and [Ti(1)(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 H NMR spectroscopy. For the conditions tested (6 mM, DMSO-d/DO: 8/1), a rather good stability with t ranging from 180 to 300 min is determined for the complexes. In the presence of an acid (DCl), the hydrolysis of [Ti(1)(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 IC ranging from 6.2 ± 1.2 μM to 274 ± 56 μM. The fluorescence studies of the ligands 2a-d, and the complexes [Ti(1)(2a-d)] reveal an important fluorescence loss of the ligands 2c and 2d upon coordination with the Ti(1) fragment. Frontier orbitals obtained by DFT calculations permit us to explain this fluorescence quenching.

Photoactive Complexes with Earth-Abundant Metals

“…Unfortunately, structurally analogous Ti­(IV) complexes with the ((ArO) 2 NHC) and Me DPD ligands were nonluminescent. , With other ligands, luminescent Ti­(IV) complexes are accessible, but so far essentially ligand-based fluorescence was observed . Zr is a second row transition metal, but a quite abundant one (Table ).…”

Bent 1,10-Phenanthroline Ligands within Octahedral Complexes Constructed around a TiO4N2 Core

“…The behavior of the selected complexes has been evaluated by following a methodology similar to that already reported for related titanium complexes. 43 These studies were conducted by 1 H NMR analysis of solutions in dimethyl sulfoxide (DMSO)-d 6 of a complex over time, upon the addition of D 2 O at room temperature. For these analyses, a large amount of D 2 O (1000 equiv versus the complex) was added so that the final concentration of the complex solution Complexes [Ti(1) 2 (2c,2d)] showed good stability in this medium.…”

“…Overall, distortion of the neocuproine ligands is observed for late-transition-metal complexes, and these deformations may be attributed in such a case to steric repulsions. 24−26 In our effort to develop multicomponent self-assembly chemistry based on TiO 4 N 2 nodes 27 and titanium complexes for biological applications, 28 we have generated a series of monomeric heteroleptic TiO 4 N 2 -based complexes incorporating two 6,6′-diphenyl-2,2′-biphenolato ligands (1; Chart 1) and various bidentate nitrogen ligands. These ligands include 1,10-phen backbones decorated with substituents positioned far from the two donating N atoms.…”

Chemistry on the Complex: Derivatization of TiO4N2‐Based Complexes and Application to Multi‐Step Synthesis

“…In our effort to generate multicomponent self-assembly architectures, [39] materials [40] and titanium complexes for biomedical purposes, [41] we have developed a series of monomeric heteroleptic complexes [42] built around a TiO 4 N 2 scaffold. These Ti(IV) species incorporate two readily available 3,3'-diphenyl-2,2'-biphenolato ligands (1; Figure 1) and various bidentate nitrogen ligands.…”