Carbon-fluorine bond cleavage in fluoroarenes via a niobium(III) imido complex: from stoichiometric to catalytic hydrodefluorination

摘要

The mechanism of activation of C-F bonds in fluoroarenes using a well-defined niobium(III) imido complex has been investigated. The Nb(III) arene species [BDI]Nb(N~tBu)(η~6-C6H6), 1, (BDI = β-diketimate), reacts stoichiometrically with fluoroarenes to yield niobium(v) aryl fluorides. Spectroscopic analysis supported by DFT calculations revealed the critical involvement of a Nb(III) fluoroarene-bound species. In contrast to previous reports of related reactivity, we found that perfluorinated arenes (i.e. those normally assumed to bear more 'activated' C-F bonds) are, in the present system, much less reactive towards C-F bond cleavage than mono- or difluoro-substituted arenes. In addition to demonstrating stoichiometric hydrodefluorination reactions, we also describe an efficient and mild hydrodefluorination of mono- and di-fluoroarenes that is catalytic in niobium.