Photoinduced Oxygen Atom Transfer to & alpha;-Pinene and R-Carvone using a Dioxo-Molybdenum (VI) Complex Incorporated within a Modified UiO-67 (Zr/Ti) MOF

We report a highly selective (100 %) epoxidation of & alpha;-pinene and R-carvone using an oxygen atom transfer (OAT) reaction facilitated by a dioxo-Mo complex (Mo((VI))O(2)Cl(2)Ln) incorporated into the ligand 5,5'-dicarboxylate-2,2'-bipyridine (bpydc) within a Metal-Organic Framework (MOF) type UiO-67. Photo-stimulated (350 nm) OAT reaction was carried out with oxygen molecular used as the oxidant for 10 h. UiO-67 was synthesized with a mixture of the ligands 2,2 & PRIME;-biphenyl-5,5 & PRIME;-dicarboxylate (bpdc) and 2,2-bipyridine-5,5-dicarboxylate (bpydc) in different molar ratios (67 : 33, 50 : 50, 70 : 30, 0 : 100 bpdc : bpydc) to promote a higher presence of catalytic sites, i. e., the dioxo-Mo complex units. Furthermore, a post-synthetic exchange of Zr for Ti, between 64 : 36 to 78 : 22 Ti : Zr molar ratio, was performed to improve the optical properties of the MOF and promote the photoinduced OAT reaction. The Catalytic system was characterized by FTIR, XRD, H-1 NMR, XPS, TGA, N-2 adsorption/desorption and UV-Vis-DR. The amount of the epoxide monoterpene is proportional to the number of the dioxomolybdenum((VI)) units (MoO2) incorporated in the UiO-67 (Zr/Ti), and the OAT reaction selectivity is due to the absence of the oxygen radicals in the medium of reaction. Besides, The Mo complex exhibited excellent stability after five cycles of use.

Automated summary

A highly selective epoxidation of α-pinene and R-carvone was achieved using a dioxo-Mo complex incorporated into a Metal-Organic Framework (MOF) type UiO-67. The reaction was facilitated by an oxygen atom transfer (OAT) using molecular oxygen as the oxidant. The catalytic system was characterized and the presence of dioxomolybdenum((VI)) units in UiO-67 was found to be proportional to the amount of epoxide monoterpene produced. Furthermore, the reaction selectivity was attributed to the absence of oxygen radicals in the reaction medium. The stability of the Mo complex was also demonstrated after multiple cycles of use.