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 1H NMR and a series of coexisting intermediate compounds such as 1,1′-bis(tri-n-butylstannyl)-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.