Mechanistic Investigation on Oxygen Transfer with the Manganese‐Salen Complex

Abstract

The best‐known application of salen complexes is the use of a chiral ligand loaded with manganese to form the Jacobsen complex. This organometallic catalyst is used in the epoxidation of unfunctionalized olefins and can achieve very high selectivities. Although this application was proposed many years ago, the mechanism of oxygen transfer remains a question until now. In this paper, the epoxidation mechanism is investigated by an ab initio kinetic modeling study. First of all a proper DFT functional is selected that yields the correct ordering of the various spin states. Our results show that the epoxidation proceeds via a radical intermediate. If we start from the radical intermediate, these results can explain the experiments with radical probes. The subtle influences in the transition state using the full Jacobsen catalyst explain the product distribution observed experimentally.

Metal–organic and covalent organic frameworks as single-site catalysts

“… 254 The selectivity was unravelled by DFT calculations, yet required the use of a proper DFT functional to yield the correct ordering of the spin states. 255 OPBE was selected from a broad range of exchange–correlation functionals, as it gave the right ordering of the spin states compared to benchmark DMRG (density matrix renormalization group) calculations. Finally, ONIOM calculations were performed to assess the influence of the confinement in the cage.…”

Strengths, Weaknesses, Opportunities and Threats: Computational Studies of Mn- and Fe-Catalyzed Epoxidations

“…As shown in Figure 4, a number of possible reaction paths are possible [45]. These include the formation of a metallaoxethane intermediate (Figure 4a), a concerted mechanism (Figure 4b), the formation of a five-membered ring structure including a nitrogen or oxygen atom of a spectator ligand, such as salen, or porphyrin (Figure 4c,d, respectively), or the formation of a carbon radical intermediate (Figure 4e) [34]. Each of these mechanisms allows the explanation of at least some of the experimental data available for these reactions, in particular the high enantioselectivity of Mn(salen)-and Fe(porphyrin)-catalyzed epoxidation of cis-olefins [23,50,69,70].…”

“…This is partly compensated by some studies that benchmark their findings across a large number of density functionals [17,31,34,133] (and eventually, other theoretical methods [23,34,35,134]). Moreover, most works accessing the performance of B3LYP acknowledge its limitations when applied to transition metal chemistry.…”

Asymmetric Epoxidation of Olefins with H2O2 Catalyzed by a Bioinspired Aminopyridine N4 Iron Complex

“…Catalytic asymmetric epoxidation of olefins has been widely recognized as a powerful tool in synthetic chemistry owing to the generating of chiral epoxides, which are versatile synthons for the construction of natural products and pharmaceutical molecules . Thus, numerous efforts have been devoted to achieving efficient catalysts, and a number of chiral metal complexes and organocatalysts have been developed successfully for the enantioselective epoxidation of a variety of alkenes .…”

“…Catalytic asymmetric epoxidation of olefins hasb een widely recognized as ap owerful tool in synthetic chemistry owing to the generating of chiral epoxides,w hich are versatile synthons for the construction of natural products and pharmaceutical molecules. [1][2][3][4][5] Thus, numerous efforts have been devoted to achieving efficient catalysts, and anumber of chiral metal complexes and organocatalysts have been developed successfully for the enantioselective epoxidation of av ariety of alkenes. [6][7][8][9] Despite enormous progress in the field, it is of great importance to explore practical asymmetrice poxidation using environmentally friendly catalysts and oxidants from the viewpoint of green chemistry.I nt his context, the development of iron catalysts with considerable activity is highly desirable,a si ron is nontoxic,c heap, and abundant.…”