Facile Synthesis and Redox Behavior of an Overcrowded Spirogermabifluorene

Shogo Morisako,Kohsuke Noro,Takahiro Sasamori

doi:10.3390/inorganics9100075

Shogo Morisako, Kohsuke Noro + Show 1 more

Open Access

https://doi.org/10.3390/inorganics9100075

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Abstract

A spirogermabifluorene that bears sterically demanding 3,3′,5,5′-tetra(t-butyl)-2,2′-biphenylene groups (1) was obtained from the reaction of in-situ-generated 2,2′-dilithiobiphenylene with GeCl2·(dioxane). The solid-state structure and the redox behavior of 1 were examined by single-crystal X-ray diffraction analysis and electrochemical measurements, respectively. The sterically hindered biphenyl ligands endow 1 with high redox stability and increased electron affinity. The experimental observations were corroborated by theoretical DFT calculations.

Highlights

With the aim of constructing redox-active molecules, biphenyl ligands are very interesting π-organic bidentate ligands that exhibit redox activity on account of the effectively conjugated benzene rings [1,2,3]
Spirobifluorenes (I) that contain two mutually perpendicular biphenylene π-frameworks on a central tetravalent carbon atom are potentially efficient optoelectronic materials due to their unique photophysical properties derived from the spiroconjugation (Figure 1) [4,5,6,7,8,9,10]
Two main methods are conceivable for the modification of the properties of spirobifluorenes: (i) functionalization on the periphery of the biphenyl skeletons and (ii) replacement of the central element, which creates heterospirobifluorenes

Summary

Introduction

With the aim of constructing redox-active molecules, biphenyl ligands are very interesting π-organic bidentate ligands that exhibit redox activity on account of the effectively conjugated benzene rings [1,2,3]. A vital requirement for such molecules as electron-transporting materials is redox stability, i.e., the anionic/cationic species generated via one-electron reduction/oxidation should exhibit relatively high stability. In this context, a heterospirobifluorene has already shown electrochemical stability upon reduction [11,12,13,14,15,16,17,18,19]. In the expectation of the formation of the overcrowded spirogermabifluorene 1, we attempted the reaction of 5 with in-situ-generated 4. Only a complicated mixture including biphenyl 2 was obtained, and evidence for the formation of the expected spirogermabifluorene 1 was not observed (Scheme 1). The isolation and identification of the reduced product of spirogermabifluorene 1 and the synthesis of its Si-analogue are currently in progress in our laboratory

General Information

Synthesis of Dichlorogermane 5

Synthesis of Spirogermabifluorene 1