Synthetic Route to 1,1′,2,2′-Tetraiodoferrocene that avoids isomerization and the electrochemistry of some tetrahaloferrocenes

An efficient synthesis of 1,1',2,2'-tetraiodoferrocene is described that uses 1,1',2,2'-tetrakis(tri-n-butylstannyl)ferrocene as a key intermediate in its synthesis. In an attempt to examine the stepwise mechanism, the reaction of the tetratin-substituted ferrocene 1,1',2,2'-tetrakis(tri-n-butylstannyl)ferrocene with iodine was monitored by 'H NMR and a series of coexisting intermediate compounds such as 1,1-bis(tri-n-butylstanny1)-2,2'-diodoferrocene were observed. The crystal structure of 1,1',2,2'-tetraiodoferrocene has been determined, and it is compared with the structure of the previously reported 1,1',2,2'-tetrabromoferrocene and 1,2,4,1'-tetraiodoferrocene. The comparative electrochemistry of 1,1',2,2'-tetrachloroferrocene, 1,1',2,2'-tetrabromoferrocene, and 1,1',2,2'-tetraiodoferrocene is described. The crystal structure of 1,2,1'-triiodoferrocene is also reported for comparative use to illustrate the scope of the synthetic method.