Unsolvated Al(C6F5)3: structural features and electronic interaction with ferrocene

Abstract

Alkyl/aryl ligand exchange between AlEt₃ and B(C₆F₅)₃ in hexanes enables the formation and isolation of the unsolvated Al(C₆F₅)₃ as a crystalline solid, the structure of which has been determined by single-crystal X-ray diffraction analysis. Instead of forming the anticipated Al⋯F contacts with the seemingly more accessible meta- and para-F's of –C₆F₅ groups, two Al(C₆F₅)₃ molecules form a dimeric structure with double Al⋯F interactions between the Al center of one molecule and the ortho-F atom of the –C₆F₅ group on the other molecule. This mode of interactions is apparently linked to the thermal and shock sensitivity of the unsolvated Al(C₆F₅)₃ in the solid state. To compare with the B(C₆F₅)₃/ferrocene frustrated Lewis pair system, the complexation between Al(C₆F₅)₃ and ferrocene has also been studied, which affords a stable adduct formed through the η¹-coordination of Al to one of the C_Cp atoms, similar to the alane–toluene or benzene complex.