Pi in the sky: 1,2‐bis(ferrocenyl)distibene and 1,2‐bis(ferrocenyl)dibismuthene derivatives, where two bulky ferrocenyl units are bridged by a SbSb and BiBi π spacer, have been synthesized as a new family of novel d–π conjugated systems. Their molecular structures, spectroscopic behavior, and electrochemical properties reveal the SbSb and BiBi units to be effective π‐electron spacers.

The synthesis and characterization of a stable 1,2-bis(ferrocenyl)diphosphene, wherein a P=P π-bond connects two ferrocenyl units will be reported. This represents an unprecedented example for a d-π electron system containing a heavier pnictogen π-spacer group. Stabilization of the highly reactive P=P π-bond was achieved by steric protection using two bulky ferrocenyl moieties.

1,2-Bis(ferrocenyl)dipnictenes bearing a Pn=Pn ³-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 ³-spacer moiety, respectively. Thus, these 1,2-bis(ferrocenyl)dipnictenes with a Pn=Pn ³-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 ³-spacer than those of 2nd row elements such as C=C and N=N.Organometallic ³-conjugated systems are attracting much interest from the viewpoint of showing interesting electronic, optical, and magnetic properties. In this research field, d³ conjugated systems of bimetallic complexes tethered with a ³-electron spacer, [M(Ligand)](³-electron spacer)[M(Ligand)] (M: transition metal), have been actively investigated.1 These compounds are a unique class of appropriate models of mixedvalence states giving insight on the ability of the ³-electron system as a ³-spacer in the context of fundamental organic electronic materials such as molecular switches and molecular wires.2 In this background, ferrocene is frequently used as an effective d-electron moiety in such d³ conjugated systems, because it should be a promisingly stable and effective redox system and amenable to modification with a variety of established substituents.3 Thus, ferrocenyl-based bimetallic d³ electron systems should be a touchstone for investigating the ability of a ³-electron system as a "³-spacer." Although several numbers of d³ conjugated systems with two ferrocenyl groups bridged by a ³-electron spacer have been reported to be investigated, e.g., Ph(Fc)C=C(Fc)Ph, 4 FcC¸CFc, 5 FcN=NFc 6 (Fc: ferrocenyl), and bis(ferrocenyl)thiophene derivatives, 7 the ³-electron systems in these compounds are limited to those consisting of 2nd row main group elements. The advantageous and required properties as a d³ electron system toward organometallic electronic materials should be (i) relatively low redox potential, (ii) stable multistep redox behavior, and (iii) controllable redox system. Regarding all of these points, ³-bonds between heavier main group elements are thought to be superior to those of 2nd row elements as a ³-spacer in d³ electron systems, because ³-bond compounds between heavier main group elements are known to exhibit smaller ³³* energy gaps than those of 2nd row elements due to the smaller overlapping of np orbitals. ...

Chalcogenation reactions of 1,2-bis(ferrocenyl)diphosphene, Fc*P=PFc* (Fc*: 2,5-bis(3,5-di-t-butylphenyl)ferrocenyl), with elemental sulfur (S8) and tellurium afforded the corresponding thia- and telluradiphosphirane derivatives as stable crystalline compounds, respectively. The sterically demanding ferrocenyl group would afford sufficient crystallinity and stability to the heterocyclic compounds; the structures of these three-membered ring heterocycles were revealed by X-ray crystallographic analysis.