Synthesis and fluxional behaviour of new “heavy fluorous” cyclopentadienes

Abstract

The new “heavy fluorous” cyclopentadienes C 5H 6− n [M(C 2H 4C 6F 13) 3] n (M = Si, n = 1 ( 3); n = 2 ( 4) and M = Sn, n = 1 ( 10)) were synthesized by reaction of cyclopentadienyl lithium with BrSi(C 2H 4C 6F 13) 3 ( 2) or commercial BrSn(C 2H 4C 6F 13) 3. Fluorous cyclopentadienes prepared in this manner contain three or six C 6F 13 groups, which significantly increase their solubility in perfluorinated solvents. They also provide intermediates for titanium complexes suitable for fluorous biphase catalysis. All three isomers of silylcyclopentadienes 3 and 4 were identified and fully characterized by two dimensional NMR spectroscopy, which was performed at low temperature. The allylic isomers 3a and 4a undergo degenerate metallotropic rearrangement. This fluxional behaviour was compared with the behaviour of previously prepared cyclopentadienes 6 and 7 (C 5H 6− n [SiMe 2(C 2H 4C 8F 17)] n where n = 1, 2, respectively). The presence of allylic isomers 6a and 7a was further confirmed by Diels-Alder cycloaddition of the strong dienophile tetracyanoethylene (TCNE), providing compounds 8 and 9.