Origin of Increased Reactivity in Rhenium-Mediated Cycloadditions of Tetrazines

02 July 2021, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Pyridyl tetrazines coordinated to metals like rhenium have been shown to be more reactive in [4+2] cycloadditions than their un-complexed counterparts. Using density functional theory (DFT) calculations, and in particular distortion/interaction and energy de-composition analysis, we analyze the factors that contribute to this increase in selectivity. The reaction of the complexed tetrazine has a more favorable interaction energy compared to the uncomplexed tetrazine, and the main contributor to this favorable interaction energy an increase in orbital interactions through a lowering of the LUMO in the complexed tetrazine. Additionally, the high regioselectivity of the reaction is shown to be due to a greater degree of charge stabilization in the transition state leading to the major prod-uct. This study suggests that the energy of the FMOs is a good indicator of reactivity in these reactions, and the enhanced [4+2] reactivity upon complexation adds another tool to the toolbox of click reactions.

Keywords

Click Chemistry
Tetrazines
Bioorthogonal
DFT
Reactivity
Selectivity

Supplementary materials

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Description
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Supporting information
Description
Energies of all discussed structures, additional energy decomposition analysis and orbital energies
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Cartesian Coordinates
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Cartesian coordinates as *.xyz for all discussed structures.
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