Exploring the peri-, chemo-, and regio-selectivity of additionof manganese metal oxides MnO3L(L=Cl ,O , OCH3,CH3)tosubstituted ketenes: A computational study

Ahmed, Issahaku; Tia, Richard; Adei, Evans

Exploring the peri-, chemo-, and regio-selectivity of additionof manganese metal oxides MnO3L(L=Cl ,O , OCH3,CH3)tosubstituted ketenes: A computational study

Date

2015-11-11

Authors

Ahmed, Issahaku

Tia, Richard

Adei, Evans

Publisher

Elsevier B.V. I.

Abstract

Ketenes are interesting reactive intermediates that find a wide range of synthetic applications. Densityfunctional theory calculations at the MO6/LACVP⁄and B3LYP/LACVP⁄levels of theory have beenemployed to explore the peri-, chemo-, and regio-selectivity of the addition of manganese oxo complexesMnO3L (L = Cl, O , OCH3,CH3) to substituted ketenes O@C@C(CH3)(X) [X = H, CH3, Cl, CN, Ph] with the aimof elucidating the effects of substituents on the mechanism of the reactions. The results show that theconcerted [3+2] addition of the C@C bond of the ketene across the metal complex is the most preferredpathway in all the reactions studied (with respect to changing ligand L on the metal complex or sub-stituent X on the ketene) except in the reaction of MnO4 (i.e. for L = O ) with dimethyl ketene, which fol-lows only a stepwise addition pathway. [2+2] addition is found to be possible only in the reaction ofMnO3–OCH3with dimethyl ketene where the activation barrier for [2+2]C@Oaddition is 23.79 kcal/mol,which is far greater than the barrier for the [3+2] addition. The reactions of dimethyl ketene withMnO4 will most likely lead to the formation of an ester precursor and the reaction of MnO3Cl with thesubstituted ketenes would lead to the formation of an ester precursor, chlorohydrin precursor, acetalde-hyde and carbon monoxide (for X = H, Cl). Generally, reactions involving an increase in oxidation state ofmetal have higher activation barriers. For both [3+2] and [2+2] addition, low activation barriers areobtained when the substituent on the ketene is electron-donating while high activation barriers areobtained when the substituent is electron-withdrawing. The reactions of ketenes with MnO3L complexeshave lower activation barriers for the preferred [3+2] and [2+2] addition pathways as well as fewer sidereactions than those of the ReO3L complexes reported in the literature, a trend which was seen in our ear-lier work with reactions of group VII metals with olefins, implying that manganese oxo complexes effi-ciently and selectively catalyze specific reactions in oxidation of ketenes and olefins than do Re oxocomplexes and therefore Mn oxo complexes may be better catalysts for specific oxidation reactions ofketenes and olefins than Re complexes are.

Description

An article published by Elsevier B.V and also available at http://dx.doi.org/10.1016/j.ica.2015.11.006

Keywords

Regioselectivity, Chemoselectivity, Ketene, Manganese oxo complex, Metalla-2,5-dioxolane, Computational

Citation

Ahmed et al./Inorganica Chimica Acta 441 (2016) 57–66. Exploring the peri-, chemo-, and regio-selectivity of additionof manganese metal oxides MnO3L(L=Cl ,O , OCH3,CH3)tosubstituted ketenes: A computational study. http://dx.doi.org/10.1016/j.ica.2015.11.006