1,2-Bis(ferrocenyl)dipnictenes bearing a Pn=Pn π-spacer (Pn: P (1), Sb (2), and Bi (3)) between two ferrocenyl units have been synthesized as stable compounds. Not only their molecular structures and fundamental properties but also their redox behavior have been systematically disclosed. Interestingly, in the reduction region, the dipnictenes showed two pseudo-reversible one-electron redox couples at low temperature, suggesting possible generation of the corresponding radical anion and dianion species. On the other hand, they showed three-step one-electron oxidation processes in the oxidation region. The first two oxidation steps would correspond to those of the two ferrocenyl moieties, while the third step would be that of the Pn=Pn π-spacer moiety, respectively. Thus, these 1,2-bis(ferrocenyl)dipnictenes with a Pn=Pn π-spacer should be stable multiredox systems reflecting unique properties of a double bond between heavier 15 group elements. As a result, all Pn=Pn units (Pn: P, Sb, and Bi) were found to work as a more effective π-spacer than those of 2nd row elements such as C=C and N=N.
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