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

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 AlF 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 AlF 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 η(1)-coordination of Al to one of the CCp atoms, similar to the alane-toluene or benzene complex.