• The first Mo/phenanthroline polymeric hybrid applied for catalytic olefin epoxidation • Robust performance of the Mo/phenanthroline hybrid catalyst for limonene valorization • Limonene to limonene oxide with TOF of thousands per hour and high selectivity • Hybrid generates soluble active species that self-construct into the original hybrid • Structure of peroxo active species inferred from catalytic and spectroscopic evidence In this work, the first Mo/phenanthroline polymeric hybrid is reported for the chemical valorization of biobased olefins via selective catalytic epoxidation. Catalytic epoxidation is of strategic importance to the chemical industry, as it produces epoxides that serve as renewable key intermediates for many end-user products. A relevant example is limonene (Lim), a terpene abundantly found in biobased waste, which can be valorized to limonene oxide (LimO) for the manufacture of renewable chemicals and materials. Molybdenum coordination compounds are effective epoxidation catalysts due to their ability to coordinate with a wide range of ligands. Among them, the bidentate N, N′ -donor ligand 1, 10-phenanthroline (phen) is attractive because of its strong affinity toward transition metals and its stable, versatile heterocyclic structure. A newly developed hybrid, namely MoO 3 (phen) (2), was synthesized from the mononuclear precursor MoO 2 Cl 2 (phen) (1) using water as the solvent. Its structure was investigated using a combination of techniques, including elemental and thermogravimetric analyses, ATR FT-IR and Raman vibrational spectroscopies, powder X-ray diffraction, and solid-state 13 C 1 H magic-angle spinning (MAS) NMR spectroscopy. This hybrid promoted the catalytic epoxidation of Lim with tert -butyl hydroperoxide at 70°C, with a turnover frequency of 2000 mol mol Mo −1 h −1 and 100% selectivity toward LimO. This study combines the identification of the structure of the active species, the investigation of catalytic reaction conditions, and mechanistic studies supported by kinetic modeling. The results suggest the formation of monooxodiperoxomolybdenum active species and a mechanism involving hydroperoxide activation followed by oxo transfer to Lim, giving LimO.
Silva et al. (Sun,) studied this question.