Abstract
We report on the highly efficient epoxidation of low-molecular-weight and polymeric olefins catalyzed by a supramolecular manganese porphyrin complex using molecular oxygen as an oxidant and an aldehyde as a co-reductant. At ambient temperature and under optimized reaction conditions, the catalyst showed high activity and stereoselectivity. The efficiency of the supramolecular manganese porphyrin was higher than that of a reference porphyrin catalyst, possibly because it was more stable under the applied reaction conditions. Mechanistic studies suggest that a manganese oxo porphyrin complex may be an intermediate in the epoxidation reaction.
Highlights
Metalloporphyrins are amongst the vital chemical compounds that are crucial for life on earth
Our group has been active in the use of supramolecular metalloporphyrins as mimics of processive enzymes, e.g., DNA polymerase, which are biological catalysts that stay bound to a substrate while performing multiple rounds of catalysis [6]
Halving the amount of isobutyraldehyde led to a dramatic drop in conversion to Subsequently, we studied the effect of the amount of the co-reductant isobutyraldehyde on the
Summary
Metalloporphyrins are amongst the vital chemical compounds that are crucial for life on earth.For example, the iron porphyrin complex heme plays a key role in the transport and delivery of molecular oxygen to animal tissues [1]. Metalloporphyrins are amongst the vital chemical compounds that are crucial for life on earth. Our group has been active in the use of supramolecular metalloporphyrins as mimics of processive enzymes, e.g., DNA polymerase, which are biological catalysts that stay bound to a substrate while performing multiple rounds of catalysis [6]. We have previously shown that a U-shaped receptor based on glycoluril with a covalently attached manganese(III) porphyrin roof, MnPC, can thread onto polymeric olefins (e.g., polybutadiene) and epoxidize them in a processive manner (Figure 1) [7,8,9]. To ensure that catalysis only takes place inside the cavity of the catalyst, a bulky axial ligand (4-tert-butylpyridine) was coordinated to the manganese center at the outside of the cage compound. In the presence of oxygen donors such as iodosylbenzene (PhIO) or sodium hypochlorite (NaOCl), the catalyst MnPC fully converted polybutadiene (Mw ≈ 300 kDa, 98% cis) into the corresponding polyepoxide within 2 hours [7]
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