Coupling and Dearomatization of Pyridines at a Transient η2 -Cyclopropene/Bicyclobutane Zirconocene Complex

bibtex: ISI:000414633200027 bibtex\location:'POSTFACH 101161, 69451 WEINHEIM, GERMANY',publisher:'WILEY-V C H VERLAG GMBH',type:'Article',affiliation:'Etienne, M (Reprint Author), CNRS, LCC, 205 Route Narbonne,BP44099, F-31077 Toulouse, France. Etienne, M (Reprint Author), Univ Toulouse, UPS, INPT, LCC, F-31077 Toulouse, France. Romero, Nuria; Dufrois, Quentin; Vendier, Laure; Dinoi, Chiara; Etienne, Michel, CNRS, LCC, 205 Route Narbonne,BP44099, F-31077 Toulouse, France. Romero, Nuria; Dufrois, Quentin; Vendier, Laure; Dinoi, Chiara; Etienne, Michel, Univ Toulouse, UPS, INPT, LCC, F-31077 Toulouse, France. Romero, Nuria, Univ Autonoma Barcelona, Dept Quim, Cerdanyola Del Valles Ba 08193, Spain. Dinoi, Chiara, LPCNO INSA, 135 Ave Rangueil, F-31077 Toulouse, France.','author-email':'michel.etienne@lcc-toulouse.fr',da:'2018-12-05','doc-delivery-number':'FM0EI',eissn:'1521-3765','funding-acknowledgement':'MENESR [ANR-11-BS07-0009]; COST Action CHAOS [CA15106]','funding-text':'We thank the MENESR for a PhD grant to QD, the ANR (Green-LAkE project; ANR-11-BS07-0009) and COST Action CHAOS (CA15106) for support.','journal-iso':'Chem.-Eur. J.','keywords-plus':'AROMATIC N-HETEROCYCLES; CH BOND ACTIVATION; CRYSTAL-STRUCTURES; ALKYL COMPLEXES; H BONDS; METAL; CHEMISTRY; ETA(2)-CYCLOPROPENE; ORGANOZIRCONIUM; NIOBIUM','number-of-cited-references':'42','orcid-numbers':'Romero, Nuria/0000-0002-2704-7779 Vendier, Laure/0000-0002-7111-9258 Etienne, Michel/0000-0002-1099-3232','research-areas':'Chemistry','researcherid-numbers':'Romero, Nuria/A-9756-2016','times-cited':'0','unique-id':'ISI:000414633200027','usage-count-last-180-days':'4','usage-count-since-2013':'12','web-of-science-categories':'Chemistry, Multidisciplinary'\; International audience; 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.