Pronounced effects of grinding on rates of intramolecular electron transfer in mixed-valence 1′,2′,1‴,2‴-tetranaphthylmethyl- and 1′,3′,1‴,3‴-tetranaphthylmethyl-biferrocenium triiodides

A series of mixed-valent (MV) complexes [(FeCp)2(mu-C10H6(BPh)2)]+X ([1+]X; X=I 5, PF6, SbF6, B(C6F5)4) were prepared by oxidation of diboradiferrocene [(FeCp)2(mu-C10H6(BPh)2)] (1) with I 2, AgPF6, and AgSbF6, respectively, and through anion exchange of the I 5(-) salt with [Li(Et2O)x][B(C6F5)4] in the case of X=B(C6F5)4. The MV state of the cation was investigated in solution by multinuclear NMR spectroscopy, CV, and UV/Vis-NIR absorption spectroscopy, and in the solid state by IR spectroscopy, single-crystal X-ray crystallography, and Mössbauer spectroscopy. The cyclic voltammogram of 1 shows two distinct redox waves with a large redox splitting of Delta E=510 mV in CH2Cl2 and the NIR spectrum for the mono-oxidized species displays an intervalence charge-transfer band at around 1500 to 1700 nm depending on the specific counterion present. The X-ray crystal structures of [1+]X show inversion-symmetric cations with X=I 5 and B(C6F5)4 and unsymmetric valence-trapped structures composed of one ferrocene and one ferrocenium moiety with X=PF6 and SbF6. Mössbauer data for X=PF6 are consistent with valence trapping at all temperatures between 90 and 343 K. In comparison, fast electron transfer is evident on the Mössbauer timescale for X=I 5 and temperature-dependent behavior is observed for X=B(C6F5)4. The anion dependence of the X-ray structural and Mössbauer data is discussed in the context of crystal symmetry and the possibility of static and dynamic disorder effects is considered.

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Examination of the Mixed‐Valence State of the Doubly Boron‐Bridged Diferrocene Cation [(FeCp)₂{μ‐C₁₀H₆(BPh)₂}]⁺

Venkatasubbaiah

Doshi

Nowik

et al. 2007

Chemistry A European J

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Zwitterionic Mixed Valence: Internalizing Counteranions into a Biferrocenium Framework toward Molecular Expression of Half‐Cells in Quantum Cellular Automata

Tahara

Terashita

Tokunaga

et al. 2019

Chemistry A European J

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Realization of molecular quantum cellular automata (QCA), a promising architecture for molecular computing through current‐free processes, requires improved understanding and application of mixed‐valence (MV) molecules. In this report, we present an electrostatic approach to creating MV subspecies through internalizing opposite charges in close proximity to MV ionic moieties. This approach is demonstrated by unsymmetrically attaching a charge‐responsive boron substituent to a well‐known organometallic MV complex, biferrocenium. Guest anions (CN− and F−) bind to the Lewis acidic boron center, leading to unusual blue‐shifts of the intervalence charge‐transfer (IVCT) bands. To the best of our knowledge, this is the first reported example of a zwitterionic MV series in which the degree of positive charge delocalization can be varied by changing the bound anions, and serves to clarify the interplay between IVCT parameters. The key underlying factor is the variable zero‐level energy difference in the MV states. This work provides new insight into imbuing MV molecules with external charge‐responsiveness, a prerequisite of molecular QCA techniques.

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(Planar‐Chiral) Ferrocenylmethanols: From Anionic Homo Phospho‐Fries Rearrangements to α‐Ferrocenyl Carbenium Ions

2017

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The reaction of FcCH2OH with chlorophosphates gave ferrocenyl phosphates FcCH2OP(O)(OR)2 [Fc = Fe(η5‐C5H5)(η4‐C5H4)], which readily separate into phosphate anions and ferrocenyl carbo‐cations. The latter species undergoes consecutive reactions, for example, electrophilic aromatic substitutions. When nitriles, instead of alcohols, are treated with FcLi or tBuLi and chlorophosphates, chiral‐pool based ferrocenylimino phosphoramidates Fc‐CR=N‐P(O)(OR*)2 are formed, which are promising candidates for anionic homo phospho‐Fries rearrangements. Moreover, the sterically demanding chiral chlorophosphate with R* enabled oxidative couplings of the imines to form a diferrocenylazine. Similarly, the reaction of Fc–Li with 9‐anthrylnitrile produced a 10‐ferrocenyl‐substituted product, contrary to a reaction at the C≡N functionality. A planar‐chiral ortho‐P(S)Ph2‐functionalized ferrocenylmethanol also gave carbo‐cations under acidic conditions. These species can be sulfurized in a unique way giving thio ethers, whereby the in situ formed 1,2‐P(S)Ph2,CH2+ ferrocene cation acts as the sulfur and electron source. However, lowering the substrate concentration prevents sulfur migration, resulting in electrophilic substitution reactions with aromatic solvents. Planar‐chiral ferrocenylmethyl thio or anisyl derivatives were applied as ligands in Pd‐catalyzed Suzuki–Miyaura C,C cross‐couplings for the atroposelective synthesis of hindered biaryls with up to 26 % ee at low catalyst loadings (1 mol‐% Pd).

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Pronounced effects of grinding on rates of intramolecular electron transfer in mixed-valence 1′,2′,1‴,2‴-tetranaphthylmethyl- and 1′,3′,1‴,3‴-tetranaphthylmethyl-biferrocenium triiodides

Cited by 8 publications

References 36 publications

Examination of the Mixed‐Valence State of the Doubly Boron‐Bridged Diferrocene Cation [(FeCp)₂{μ‐C₁₀H₆(BPh)₂}]⁺

Examination of the Mixed‐Valence State of the Doubly Boron‐Bridged Diferrocene Cation [(FeCp)₂{μ‐C₁₀H₆(BPh)₂}]⁺

Zwitterionic Mixed Valence: Internalizing Counteranions into a Biferrocenium Framework toward Molecular Expression of Half‐Cells in Quantum Cellular Automata

(Planar‐Chiral) Ferrocenylmethanols: From Anionic Homo Phospho‐Fries Rearrangements to α‐Ferrocenyl Carbenium Ions

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Pronounced effects of grinding on rates of intramolecular electron transfer in mixed-valence 1′,2′,1‴,2‴-tetranaphthylmethyl- and 1′,3′,1‴,3‴-tetranaphthylmethyl-biferrocenium triiodides

Cited by 8 publications

References 36 publications

Examination of the Mixed‐Valence State of the Doubly Boron‐Bridged Diferrocene Cation [(FeCp)2{μ‐C10H6(BPh)2}]+

Examination of the Mixed‐Valence State of the Doubly Boron‐Bridged Diferrocene Cation [(FeCp)2{μ‐C10H6(BPh)2}]+

Zwitterionic Mixed Valence: Internalizing Counteranions into a Biferrocenium Framework toward Molecular Expression of Half‐Cells in Quantum Cellular Automata

(Planar‐Chiral) Ferrocenylmethanols: From Anionic Homo Phospho‐Fries Rearrangements to α‐Ferrocenyl Carbenium Ions

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Examination of the Mixed‐Valence State of the Doubly Boron‐Bridged Diferrocene Cation [(FeCp)₂{μ‐C₁₀H₆(BPh)₂}]⁺

Examination of the Mixed‐Valence State of the Doubly Boron‐Bridged Diferrocene Cation [(FeCp)₂{μ‐C₁₀H₆(BPh)₂}]⁺