Redox-Active Titanium–2-Phenylbenzoxazole Solids as Light-Responsive Materials for Photocatalysis under Ambient Conditions

The reaction of 2-phenylbenzoxazole (BZX) with TiCl 4 in toluene under ambient aerobic conditions produces a multicolored, microcrystalline solid composed of titanium complexes in all three oxidation states (Ti(IV), Ti(III), and Ti(II)). This spontaneously formed material arises through coupled redox and hydrolytic processes, yielding a structurally and chemically diverse ensemble of coordination compounds. MALDI-TOF mass spectrometry reveals both hydrolyzed and partially degraded BZX ligands, while NMR ( 1 H, 13 C) indicates restricted rotation, chelation, and ligand rearrangement. IR spectroscopy confirms the presence of Ti–OH and Ti–O–N motifs with extensive hydrogen bonding. UV–vis absorption between 360 and 480 nm is consistent with ligand-to-metal charge transfer and d–d transitions from reduced titanium centers. Under visible light and ambient air, the mixed-valent titanium–BZX solid functions as a redox-active photocatalyst. It captures atmospheric CO 2 and H 2 O, converting them into formaldehyde and C 2 –C 8 condensation products without sacrificial agents. Catalyst hydrolysis yields 2-phenylbenzoxazoline, which reacts with CO 2 via insertion into Ti–N bonds to form titanium carbonates. The system proceeds through a visible-light-driven cascade: titanium reduction by hydroxyl radicals and aldol-type C–C bond formation with in situ generated formaldehyde. The material remains catalytically active over several days, exhibiting long-term stability and adaptive behavior. These results establish a spontaneously assembled titanium coordination material with built-in redox activity, light responsiveness, and structural plasticity. This material offers a scalable platform for artificial photosynthesis, carbon capture, and sustainable fuel synthesis.