Coupling and Dearomatization of Pyridines at a Transient (2)-Cyclopropene/Bicyclobutane Zirconocene Complex - INSA Toulouse - Institut National des Sciences Appliquées de Toulouse Access content directly
Journal Articles Chemistry - A European Journal Year : 2017

Coupling and Dearomatization of Pyridines at a Transient (2)-Cyclopropene/Bicyclobutane Zirconocene Complex

Abstract

This paper reports on stereospecific coupling reactions between an (2)-cyclopropene ligand and pyridine derivatives, which are preferred to alternative C-H bond activation reactions. The dicyclopropylzirconocene complex [Cp2Zr(c-C3H5)(2)](1) eliminates cyclopropane to generate the (2)-cyclopropene/bicyclobutane intermediate [Cp2Zr((2)-c-C3H4)](A). A does not activate any pyridine C-H bonds, but rather pyridine inserts into a Zr-C bond of A, yielding an azazirconacycle with a dearomatized pyridyl group [Cp2Zr\(2)-N,C-8-(2-c-C3H4)-C5H5N\](2). Kinetic data, isotopelabelling experiments, and DFT calculations indicate that the rate-determining step of this stereospecific reaction is cyclopropane elimination, and that the stability of the intermediate [Cp2Zr((2)-c-C3H4)(NC5H5)](A-py) governs the selectivity of the reaction. Complex2 tautomerizes to [Cp2Zr\(2)-N,C-8-(2-C3H5)-C5H4N\](6) through a base-catalyzed proton migration accompanied by cyclopropyl opening and restoration of conjugation within the zirconacycle.
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Dates and versions

hal-01961157 , version 1 (19-12-2018)

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Nuria Romero, Quentin Dufrois, Laure Vendier, Chiara Dinoi, Michel Etienne. Coupling and Dearomatization of Pyridines at a Transient (2)-Cyclopropene/Bicyclobutane Zirconocene Complex. Chemistry - A European Journal, 2017, 23 (62), pp.15766--15774. ⟨10.1002/chem.201703371⟩. ⟨hal-01961157⟩
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