Electrochemical Properties of 9,9 '-Spiro-Bifluorenes Containing Group 14 Elements (C, Si, Ge, Sn)

Cyclic voltammograms of four spiro-bifluorenes involving C (I), Si (II), Ge (III) and Sn (IV) as the central atom were recorded in acetonitrile-dichloromethane. Each substrate afforded one irreversible oxidation wave (between 1.7 to 1.9 V, vs. Ag/AgCl) and one irreversible reduction wave between -2.0 to -2.3 V (except for the Ge derivative III that showed a second irreversible reduction wave). Controlled potential anodic oxidation was executed for II-IV on a Pt anode. Surprisingly, each one of the substrates behaved differently: II yielded biphenyl (92 %) as the major product; III afforded moderate yields of a germafluorene dimer containing Ge-Ge bond (35 %) and 1,3,5-triphenylbenzene 10 (22 %), and IV formed the aromatic derivative 10 as the major product (76 %). In all cases, chlorinated products were formed too. A plausible mechanism for the formation of the variety of products is suggested.