Intercalation of a molybdenum(0)-tetracarbonyl–bipyridine complex in a layered double hydroxide

A Zn,Al layered double hydroxide (LDH) intercalated by cis-[Mo(CO)4(bpdc)]2− anions (bpdc = 2,2′-bipyridine-5,5′-dicarboxylate) has been prepared by ion exchange of a Zn,Al–NO3 LDH precursor, and characterized by powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), FT-IR, FT-Raman and UV–Vis spectroscopies. The ion exchange method gives rise to a highly organized intercalate with up to six (00l) basal reflections in the powder XRD pattern. The interlayer spacing of 18.0 Å indicates that the material contains a monolayer of guest anions positioned in such a way that the bpdc ligands are arranged with their longest dimension roughly perpendicular to the hydroxide layers of the host. Spectroscopic studies confirm the presence of structurally intact cis-[Mo(CO)4(bpdc)]2− anions in the freshly prepared material, while also showing that the guest anions undergo slow decarbonylation over a period of several days, which is accelerated upon exposure of the material to light and air. The oxidative decarbonylation can be performed rapidly by reaction of the LDH containing intercalated tetracarbonyl complexes with tert-butylhydroperoxide, leading to intercalated molybdenum oxide/bipyridine species, which may be polymeric species of the type [MoO3(bpdc)]2−. Catalytic tests for the epoxidation of olefins and the oxidative dehydrogenation of alcohols were carried out for this material.