Reusable manganese compounds containing pyrazole-based ligands for olefin epoxidation reactions

Abstract

We describe the synthesis of new manganese (II) and manganese (III) complexes containing the bidentate ligands 2-(3-pyrazolyl)pyridine, pypz-H, and 3 (5) These observations have been explained through computational calculations. The reutilization of catalysts 1 and 6 for the epoxidation of alkenes has been evaluated in [bmim]:acetonitrile mixture (bmim = 1-butyl-3-methylimidazolium), allowing the effective recyclability of the catalytic system and keeping high conversion and selectivity values up to 12 successive runs, in all cases.

Pesticides Curbing Soil Fertility: Effect of Complexation of Free Metal Ions

“…For all species the ground state multiplicity has been checked and, for the sake of consistency, the corresponding state for metal ion is maintained whatever pesticide ligands surround it afterwards (Manrique et al, 2015). Anyway, and fortunately no multiplicity crossing is observed (Poater et al, 2014; Gil-Sepulcre et al, 2016).…”

A Recoverable Ruthenium Aqua Complex Supported on Silica Particles: An Efficient Epoxidation Catalyst

“…An interesting reaction in catalytic epoxidation is the stereoselectivee poxidation of cis alkenes, [19][20][21][22][23][24] in which the wellknown and efficient Mn salen complexes [25] and others [26] generally give mixtures of cis and trans epoxides. The cis!trans isomerization in epoxidation processes involving cis alkenes is ac ommon phenomenon due to the higher thermodynamic stabilityo ft he trans epoxides.T ou ndergo such isomerization, rotationa round the CÀCb ond is required involving the presence of ar elatively long lived substrate free radical during the oxygen-transfer process.…”

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

“…More recently, Manrique et al [80] also proposed the existence of a radical intermediate to justify the incomplete stereoselectivity for the epoxidation of cis-β-methyl styrene by pyrazole-manganese(II) and pyrazole-manganese(III) catalysts. One peculiarity in this study is the fact that it uses a mixed level of theory: the relatively expensive geometry optimizations (including the search for transition state structures) and evaluation of the nuclear Hessian were done using a local density functional (M06L) in conjunction with a relatively small basis set (Aldrich's split-valence, with a more sophisticated relativistic SDDbasis set on Mn).…”

“…Despite this, an interesting strategy to achieve a compromise between accuracy and the economy of computational effort is exemplified in the work of Manrique et al [80], where the most computationally-demanding tasks (geometry optimization and evaluation of the vibrational spectra) are done at a lower level of theory, providing the thermal and zero-point energy components of the absolute enthalpies and Gibbs energies. In their turn, the electronic energy is calculated at a higher (more expensive) level of theory at a fixed geometry, with the eventual inclusion of solvent effects using the PCM framework.…”

“…These calculations provided the geometry and also the enthalpic and entropic corrections needed for calculating absolute Gibbs energies. However, the electronic component of the Gibbs energy was refined using single-point calculations performed with a functional that includes exact exchange (M06), a more flexible basis set (TZVP) and also the inclusion of solvent effects using PCM [80].…”