Synthesis and structure of fluorinated dialacycles

Addition of THF to a solution of dimeric 1,2-bis(chloromethylalumino) tetra fluorobenzene (1) induces a ring contraction process that results in the fo rmation of a mixture of three dialacycles as shown by H-1- and F-19-NMR. Th e three diaalacycles have been identified as 9-methyl-10-chloro-9,10-dihydr o-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-dimet hyl-9,10-dihydro-9,10-diala-octafluoroanthracene bis(THF) adduct (2c). A co -crystal of these three compounds was examined by X-ray crystallography, co nfirming the structure of the dialacycle and revealing that the central six -membered ring is in a chair conformation. In 2, each aluminum center is fo ur-coordinate with a slightly distorted tetrahedral geometry. The coordinat ion sites of the aluminum are occupied by the Ipso-carbon atoms of the tetr afluorophenylene units, the oxygen atom of a coordinated THF molecule, and either a methyl group (50%) or a chloride ion (50%). (C) 2000 Elsevier Scie nce S.A. All rights reserved.