Heteroatom-Bridged ortho-Biferrocenes: Stereoselective Synthesis, Structural Features, and Electrochemical Properties

Abstract

A versatile synthetic protocol is described for the synthesis of heteroatom-bridged biferrocene derivatives, including the symmetric species 2-SnSn and the planar-chiral species 2-SnSi, 2-BSi, and 2-SnP. Treatment of (pR,S S )-2lithio-1-(p-tolylsufinyl)-ferrocene with 0.5 equiv of Me 2 SnCl 2 afforded the tin-bridged biferrocene 1-Sn. A second Sn, Si, or P bridge was then incorporated by substitution of the sulfinyl group in the ortho-position with a dimethylstannyl, dimethylsilyl, or tert-butylphosphino group, respectively, to give the doubly bridged biferrocenes 2-SnSn, 2-SnSi, and 2-SnP. The dimethylstannyl moiety of 2-SnSi was subsequently replaced with a borane bridge via a two-step transmetalation procedure comprising treatment with HgCl 2 , followed by PhBCl 2 . The formation of ferrocene-fused six-membered heterocycles was confirmed by multinuclear NMR spectroscopy and highresolution MS analyses. The stereochemical configuration of the chiral biferrocenes 2-SnSi, 2-SnP, and 2-BSi was studied by single-crystal X-ray diffraction, chiral HPLC, and optical rotation measurements. The redox characteristics and absorption properties were investigated as well. The longest wavelength absorption experienced a bathochromic shift and an increase in intensity for 2-BSi relative to 2-SnSn and 2-SnSi, indicative of significant charge transfer character. The cyclic voltammograms of 2-SnSn and 2-SnSi displayed two separate one-electron oxidations as expected for the presence of two ferrocene units in close proximity to one another. The incorporation of boron in 2-BSi resulted in an anodic shift of both oxidation waves and an enlarged peak potential separation. The chemical oxidation of 2-BSi was carried out with [Ag(CH 2 Cl 2 )]{Al[OC(CF 3 ) 3 ] 4 }, and the reaction was monitored by NMR spectroscopy. Attempts to crystallographically characterize the corresponding doubly oxidized species proved unsuccessful.

Tunable SiN Hybrid Conjugated Materials

“…Although these results are outside the range viewed as establishing analytical purity, they are provided to illustrate the best values obtained to date. Additionally, low carbon content in organosilane elemental analysis has previously been attributed to incomplete combustion related to SiC formation. , UV–vis spectroscopy was performed on a Shimadzu UV-1800 UV–vis spectrophotometer. The UV–vis spectra were measured at room temperature in pentane in a quartz cuvette (10 mm).…”

“…Additionally, low carbon content in organosilane elemental analysis has previously been attributed to incomplete combustion related to SiC formation. 48,49 UV−vis spectroscopy was performed on a Shimadzu UV-1800 UV−vis spectrophotometer. The UV−vis spectra were measured at room temperature in pentane in a quartz cuvette (10 mm).…”

Anion-Ordering Phase Transitions in Biferrocenium and Ferrocenium Salts with the Bis(trifluoromethanesulfonyl)amide Anion

“…Biferrocenyl compounds exhibit intriguing redox properties and valence states. − In particular, the valence tautomerization of biferrocenium cations containing Fe­(II) and Fe­(III) (Figure ) has attracted significant attention in terms of mixed-valency and crystal engineering. − The biferrocenium cation has an inherently unsymmetrical structure. However, rapid electron exchange in the biferrocenium cation leads to the observation of an average-valence structure on the time scales of X-ray diffraction and Mössbauer spectroscopy.…”