From ferrocene to decasubstituted enantiopure ferrocene-1,1′-disulfoxide derivatives

Abstract

The functionalization of (R,R)-S,S′-di-tert-butylferrocene-1,1′-disulfoxide by deprotolithiation-electrophilic trapping sequences was studied towards polysubstituted, enantiopure derivatives for which the properties were determined. While the 2,2′-disubstituted ferrocene derivatives were obtained as expected, subsequent functionalization of the 2,2′-di(phenylthio) and 2,2′-bis(trimethylsilyl) derivatives occurred primarily at the 4- or 4,4′-positions. This unusual regioselectivity was discussed in detail in light of pK_a values and structural data. The less sterically hindered 2,2′-difluorinated derivative yielded the expected 1,1′,2,2′,3,3′-hexasubstituted ferrocenes by the deprotometallation-trapping sequence. Further functionalization proved possible, leading to early examples of 1,1′,2,2′,3,3′,4,4′-octa, nona and even decasubstituted ferrocenes. Some of the newly prepared ferrocene-1,1′-disulfoxides were tested as ligands for enantioselective catalysis and their electrochemical properties were investigated.