A Titanium-Organic Framework as an Exemplar of Combining the Chemistry of Metal- and Covalent-Organic Frameworks

A crystalline material with a two-dimensional structure, termed metal-organic framework-901 (MOF-901), was prepared using a strategy that combines the chemistry of MOFs and covalent-organic frameworks (COFs). This strategy involves in situ generation of an amine-functionalized titanium oxo cluster, Ti₆O₆(OCH₃)₆(AB)₆ (AB = 4-aminobenzoate), which was linked with benzene-1,4-dialdehyde using imine condensation reactions, typical of COFs. The crystal structure of MOF-901 is composed of hexagonal porous layers that are likely stacked in staggered conformation (hxl topology). This MOF represents the first example of combining metal cluster chemistry with dynamic organic covalent bond formation to give a new crystalline, extended framework of titanium metal, which is rarely used in MOFs. The incorporation of Ti(IV) units made MOF-901 useful in the photocatalyzed polymerization of methyl methacrylate (MMA). The resulting polyMMA product was obtained with a high-number-average molar mass (26 850 g mol^-1) and low polydispersity index (1.6), which in many respects are better than those achieved by the commercially available photocatalyst (P-25 TiO₂). Additionally, the catalyst can be isolated, reused, and recycled with no loss in performance.