Synthesis and structure of fluorinated dialacycles

Addition of THF to a solution of dimeric 1,2-bis(chloromethylalumino) tetrafluorobenzene (1) induces a ring contraction process that results in the formation of a mixture of three dialacycles as shown by 1H- and 19F-NMR. The three diaalacycles have been identified as 9-methyl-10-chloro-9,10-dihydro-9,10-diala-octafluoroanthracene bis(THF) adduct (2a), 9,10-dichloro-9,10-dihydro-9,10-diala-octafluoroanthracene bis(THF) adduct (2b) and 9,10-dimethyl-9,10-dihydro-9,10-diala-octafluoroanthracene bis(THF) adduct (2c). A co-crystal of these three compounds was examined by X-ray crystallography, confirming the structure of the dialacycle and revealing that the central six-membered ring is in a chair conformation. In 2, each aluminum center is four-coordinate with a slightly distorted tetrahedral geometry. The coordination sites of the aluminum are occupied by the ipso-carbon atoms of the tetrafluorophenylene units, the oxygen atom of a coordinated THF molecule, and either a methyl group (50%) or a chloride ion (50%).