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Heteroatom-Bridged ortho-Biferrocenes: Stereoselective Synthesis, Structural Features, and Electrochemical Properties
journal contribution
posted on 2016-06-01, 19:04 authored by Jiawei Chen, Alain
C. Tagne Kuate, Roger A. Lalancette, Frieder JäkleA 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,SS)-2-lithio-1-(p-tolylsufinyl)-ferrocene with 0.5 equiv of Me2SnCl2 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 HgCl2, followed by
PhBCl2. The formation of ferrocene-fused six-membered heterocycles
was confirmed by multinuclear NMR spectroscopy and high-resolution
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(CH2Cl2)]{Al[OC(CF3)3]4}, and the reaction was monitored by NMR spectroscopy. Attempts
to crystallographically characterize the corresponding doubly oxidized
species proved unsuccessful.
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Keywords
p RSnSnSnSimultinuclear NMR spectroscopy0.5 equivcharge transfer characteranodic shiftdimethylstannyl moietycyclic voltammogramsMS analysesStereoselective Synthesisoxidation waveschiral HPLCbiferroceneHgCl 2bathochromic shifttransmetalation procedurewavelength absorptionchemical oxidationPhBCl 2rotation measurementsferrocene unitsBSisulfinyl group2 SnCl 2P bridgeredox characteristicsElectrochemical PropertiesStructural FeaturesSnPspeciesborane bridgestereochemical configurationNMR spectroscopyabsorption propertiesbutylphosphino group
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