This paper addresses the problem of the strong and inert C−F bond activation of various fluoropyridines by zirconocene derivatives. Dicyclopropylzirconocene, [Cp 2 Zr(c-C 3 H 5 ) 2 ], thermally eliminates cyclopropane, giving the transient intermediate zirconabicyclobutane [Cp 2 Zr(η 2 -c-C 3 H 4 )] that cleaves a C−F bond of pentafluoropyridine selectively at position 2, forming new Zr−F and C−C bonds stereoselectively to give [Cp 2 ZrF{c-cis-CHCH 2 CH(2-NC 5 F 4 )}]. DFT computations indicate the selectivity results from the initial formation of an azazirconacycle intermediate that undergoes ring opening and C−F bond cleavage. Transmetalation with a variety of cyclopropyl donors yields [Cp 2 Zr(c-C 3 H 5 ){c-cis-CHCH 2 CH(2-NC 5 F 4 )}] with the selectivity depending on the nature of the donor. A synthetic cycle is realized when [Cp 2 Zr(c-C 3 H 5 ){c-cis-CHCH 2 CH(2-NC 5 F 4 )}] reacts with pentafluoropyridine, yielding 2-(c-C 3 H 5 )NC 5 F 4 and [Cp 2 ZrF{c-cis-CHCH 2 CH(2-NC 5 F 4 )}] with C−F bond activation. Attempts at converting this reaction sequence to a catalytic version failed due to either decomposition of the active species or multiple C−F bond substitutions by the transmetalating agent.
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