Synthesis, structure and properties of the macrocyclic ferrocenophanes with cyclopentadienyl ligands tethered by oligo(ethylene glycol) chain

Cyclization reactions of Fe{C₅H₄OCH₂(CH₂OCH₂)_nCH₂OTs}₂ (n = 1, 2) with C₆H₄-1,2-(OH)₂, C₆H₄-1,3-(OH)₂, and Fe(C₅H₄OAc)₂ under basic conditions yield the corresponding macrocyclic 1,1′-ferrocenophanes. The ferrocenophane having a pyrido-crown ether structure was also synthesized. These ferrocenophanes were characterized by X-ray crystallography and NMR spectroscopy. Cyclic voltammograms of the ferrocenophanes exhibited reversible redox peaks assigned to the oxidation and reduction of the ferrocene unit. The macrocyclic pyrido-containing ferrocenophane forms pseudorotaxane with [NH₂{(CH₂)₉Me}₂]BARF (BARF = B{C₆H₃-3,5-(CF₃)₂}₄) in CDCl₃.     

Diastereoselective ortho-lithiation of [5]ferrocenophanes

Planarly chiral ferrocene derivatives with bridged cyclopentadienyl rings are interesting ligands in asymmetric catalysis. A planar stereogenic unit is conveniently introduced by diastereoselective ortho-lithiation. The directed lithiation of several [5]ferrocenophane derivatives followed by quenching with chlorodiphenylphosphane led to planarly chiral ligands. The sense of diastereoselection was studied by computational methods. Absolute configuration of methoxy phosphane was determined by single crystal X-ray diffraction study.     

Preparation and electrochemical properties of SAM of alkanethiols functionalized with 2-aza[3]ferrocenophane on gold electrode

Thiols functionalized with N-aryl[3]azaferrocenophane formulated as HS-(CH₂)_n-N(CH₂Cp)₂Fe (1: n = 6, 2: n = 8, 3: n = 10, 4: n = 12) and disulfide obtained by oxidation of 4 (5) were synthesized via three or four steps reactions starting from 1,1′-ferrocenedimethanol, 4-aminophenol, and α,ω-aklanedithiol. Self-assembled monolayers (SAMs) of these thiols and disulfide on gold electrode were prepared by immersing the electrode in MeCN solutions of the compounds. Cyclic voltammograms of the SAM of 1 (n = 6) exhibited reversible redox of the Fe center at E_1/2 = 0.26 V (vs. Ag⁺/Ag) in the presence of Et₄NBF₄ in MeCN and at E_1/2 = 0.40 V (vs. AgCl/Ag) in the presence of NaClO₄ in H₂O. Addition of HClO₄ to the solutions shifted the redox peaks to higher potentials, E_1/2 = 0.51 V (vs. Ag⁺/Ag) in MeCN and E_1/2 = 0.48 V (vs. AgCl/Ag) in H₂O, respectively, which was ascribed to positive charge of tertiary ammonium group formed by protonation of the amino group of the azaferrocenophane. E_1/2 of SAM of 1 in H₂O solution varies depending on the anion contained in the electrolyte, NaClO₄ (0.40 V), NaBF₄ (0.46 V), Na₂SO₄ (0.53 V), and NaCl (0.55 V). Kinetic data of electron transfer between the Fe center and the gold surface of the SAM of 2-4 were obtained with variable scanning rate. Laviron’s analysis provided tunneling constant β, 0.05 Å⁻¹, suggesting that the structural changes in the SAMs on oxidation/reduction undergoes the insignificant change of the kinetic constants of the electron transfer depending on the range of the spacer length. In the acidic aqueous media, the kinetic parameters indicated that the imbalanced electron transfer between oxidized and reduced states of the Fe center was caused by the protonation of bridged amine group of azaferrocenophane.     

Molecular structure and electrochemical properties of the Pt complex of 1,1′-bis(methylthio)ferrocene and the Pd complexes of 1,4,7-trithia[7]- and 1,5,9-trithia[9] (1,1′)ferrocenophanes

Molecular structures of (triphenylphosphine) [1,1′-bis-(methylthio)ferrocene-S,S′,Fe]Pt(BF₄)₂ (1), (1,5,9-trithia[9]ferrocenophane-S,S′,S″,Fe)Pd(BF₄)₂ (2), and (acetonitrile)(1,4,7-trithia[7]ferrocenophane-S,S′,S″,Fe)Pd(BF₄)₂ (3) were determined by X-ray analyses. The Pt in 1 and the Pd atom in 2 have a somewhat distorted square-planar geometry including the Fe atom of the ferrocene moiety, while the Pd atom in 3 is coordinated by one equivalent of acetonitrile and takes a distorted tetragonal-pyramidal geometry. The distances of the Fe---M bond (M = Pd, Pt) in 1–3 are 2.851(2), 2.827(2), and 3.0962(8) Å, respectively. Cyclic voltammetry of 1–3 gave no reversible wave, but afforded some information supporting the presence of a dative bond.     

Syntheses and structural characterization of some mono- and di-p-nitrophenyl[3]ferrocenophanes: X-ray structure of [3]ferrocenophane, 3-p-nitrophenyl[3]ferrocenophane, and 3,4′-bis-(p-nitrophenyl)[3]ferrocenophane; DFT calculations on ferrocene derivatives

[3]Ferrocenophane (3a) reacts in a Gomberg reaction with diazotized p-nitroaniline to give a mixture of mono- and di-substituted products. The isomeric pairs of 3- and 2-(p-nitrophenyl)[3]ferrocenophanes (4 and 5), as well as 3,4′- and 3,4-bis-(p-nitrophenyl)[3]ferrocenophanes (6 and 7) were separated from the mixture by column chromatography on Al₂O₃ and characterized by means of mass, IR, UV, ¹H-NMR spectroscopy, and by X-ray analysis (4 and 6). PM3/tm and density functional theoretical calculations on ferrocene (1) and ferrocenophane derivatives are reported. A refined X-ray structure determination of [3]ferrocenophane (3a) is given.     

Photoinduced iron-cyclopentadienyl (Fe-Cp) bond cleavage reactions and photocontrolled polymerizations of strained [1]ferrocenophanes

Although extensive previous studies have shown that strained [1]ferrocenophanes predominantly undergo ring-opening chemistry at the bridging atom E-cyclopentadienyl (E-Cp) bond, recent reports have highlighted that reactivity at the Fe-Cp bond can also occur, especially on photoactivation. We provide an overview of recent results from our group and those of other researchers. In addition, the development of photocontrolled living polymerizations of sila[1]ferrocenophanes using Fe-Cp bond cleavage chemistry is described.     

A general synthesis of N-aryl- and N-alkyl-2-aminobenzoxazoles

An efficient and practical synthetic procedure is described for the preparation of a variety of N-substituted aryl- and alkyl-2-aminobenzoxazoles. This new method offers broad utility and provides desired products in good to excellent yield. The title compounds are formed in a one-pot, two step reaction sequence that is safe and operationally straightforward.     

含电子给体乙炔二茂铁化合物的光谱及电化学性质

合成了三种含电子给体乙炔基桥连二茂铁化合物Fc—C≡C—Ph—(p-OMe)(3a),Fc—C≡C—Ph—(p-NMe2)(3b)与Fc—C≡C—Ph—(p-NPh2)(3c),并对其结构、光化学及电化学性质进行了表征.吸收光谱表明,所有化合物在可见光区400-550nm都可归属为Fe(II)→Cp—C≡C—Ph—(p-R)(Cp为环戊二烯基)的金属到配体的电荷跃迁(MLCT)光谱,同时检测到3a与3c氧化态在近红外区(分别位于946与1044nm)可归属为Cp—C≡C—Ph—(p-R)→Fe(III)的配体到金属的电荷跃迁(LMCT).电化学测试结果表明,三种化合物都有稳定的Fc+/Fc可逆氧化还原电位,且3b与3c还出现Ph—NR2的氧化电位.3b对质子表现出光及电化学敏感性,随着质子的加入,其MLCT光谱红移,Fc+/Fc电位正移,而Ph—NR2+/Ph—NR2峰消失.     

[3]Ferrocenophanes with a tetramethyldisiloxane bridge: Synthesis and molecular structure

Summary 6,6,8,8-Tetramethyl-7-oxa-6,8-disila[3]ferrocenophane2 was obtained from the di(alkoxysilyl) ferrocene (H₄C₅SiMe₂OR)₂Fe (R=CH₂CH₂OCH₂CH₂OCH₂CH₂OMe) by hydrolysis and subsequent intramolecular disiloxane formation. 2,2,3,3,4,4,5,5,6,6,8,8-Dodecamethyl-7-oxa-6,8-disila-[3]ferrocenophane3 was formed by air oxidation of 2,23,3,4,4,5,5,6,6,7,7-dodecamethyl-6,7-disila[2]ferrocenophane. The crystal structures of both compounds were determined by single-crystal X-ray diffraction (2:a=8.5330(10),b=15.610(3),c=18.774(5)Å, =70.68(2), =77.94(2), =75.150(10)°,V=2259.8(8)ų,Z=6, space group P ,R=0.045,R _w =0.044;3:a=12.388(3),b=9.924(3),c=19.136(10)Å, =105.11(3)°,V=2271.2(15)ų,Z=4, space group P2₁/c,R=0.076,R _w =0.060). Owing to the flexibility of the disiloxane bridge,2 and3 are unstrained molecules.

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[3]Ferrocenophane mit Tetramethyldisiloxan-Brücke: Synthese und Molekülstruktur

Zusammenfassung 6,6,8,8-Tetramethyl-7-oxa-6,8-disila[3]-ferrocenophan2 entsteht aus dem Di(alkoxysilyl)ferrocen (H₄C₅SiMe₂OR)₂Fe (R=CH₂CH₂OCH₂CH₂OCH₂CH₂OMe) durch Hydrolyse und anschließende intramolekulare Disiloxan-Bildung. 2,2,3,3,4,4,5,5,6,6,8,8-Dodecamethyl-7-oxa-6,8-disila[3]ferrocenophan3 wurde durch Luftoxidation von 2,2,3,3,4,4,5,5,6,6,7,7-Dodecamethyl-6,7-disila[2]ferrocenophan erhaeten. Die Kristallstrukturen beider Verbindungen wurden durch Einkristall-Röntgenstrukturanalyse bestimmt (2:a=8.5330(10),b=15.610(3),c=18.774(5)Å, =70.68(2), =77.94(2), =75.150(10)°,V=2259.8(8)ų,Z=6, Raumgruppe P ,R=0.045,R _w =0.044;3:a=12.388(3),b=9.924(3),c=19.136(10)Å, =105.11(3)°,V=2271.2(15)ų,Z=4, Raumgruppe P2₁/c,R=0.076,R _w =0.060). Wegen der Flexibilität der Disiloxan-Brücke sind2 und3 ungespannte Moleküle.

     

Studies in N-amino-3-aza Cope rearrangements

The first examples of a N-amino-3-aza Cope rearrangement as well as the first N-amino-anion 3-aza Cope rearrangement are reported. These occur in good to excellent yields and in short reaction times.     

A novel intramolecular Ugi 3CC for the synthesis of N-alkyl-3-oxo-2-aryl-1,2,3,4-tetrahydropyrazino[1,2-a]indole-1-carboxamides

An intramolecular Ugi reaction of 2-(2-formyl-1H-indol-1-yl)acetic acid with aryl amines and isocyanides has been developed to produce a novel class of N-alkyl-3-oxo-2-aryl-1,2,3,4-tetrahydropyrazino[1,2-a]indole-1-carboxamides in good yields. This is the first report on intramolecular Ugi three component reaction of 2-(2-formyl-1H-indol-1-yl)acetic acid, aryl amine, and isonitrile.     

Synthesis, luminescence properties, and theoretical insights of N-alkyl- or N,N-dialkyl-pyrene-1-carboxamide

We report the synthesis and photophysical properties of N-alkyl- or N,N-dialkyl-pyrene-1-carboxamide. These derivatives, as well as pyrene, exhibited blue emission. N-Alkyl-type derivatives exhibited strong fluorescence emission (Φ_fl = 0.61 in EtOH) in both nonpolar and polar solvents. On the other hand, N,N-dialkyl-type derivatives showed weak fluorescence emission (Φ_fl <0.01) due to vibrational deactivation. However, in highly viscous solvents such as glycerin, the quantum efficiencies of N-alkyl-type (Φ_fl = 0.91) and N,N-dialkyl-type (Φ_fl = 0.082) derivatives were increased. We also investigated the fluorescence mechanism of these compounds using time-dependent density-functional theory (TD-DFT). From these results, we find that highly fluorescent pyrene-1-carboxamide derivatives can be designed by introducing an appropriate functional group at the nitrogen atom of the amide. Thus, N,N-dialkyl-type pyrene-1-carboxamide has considerable potential for use in applications such as environmental response sensors and probes.     

The Influence of the Counterions [AsF6]– and [GeF6]2– on the Structure of the [ClSO2NH3]+ Cation

Chlorosulfonamide reacts in the superacidic solutions HF/GeF₄ and HF/AsF₅ under the formation of ([ClSO₂NH₃]⁺)₂[GeF₆]^2– and [ClSO₂NH₃]⁺[AsF₆]^–, respectively. The chlorosulfonammonium salts were characterized by X‐ray single crystal structure analysis as well as vibrational spectroscopy and discussed together with quantum chemical calculations. ([ClSO₂NH₃]⁺)₂[GeF₆]^2– crystallizes in the triclinic space group P1 with one formula unit in the unit cell. [ClSO₂NH₃]⁺[AsF₆]^– crystallizes in the monoclinic space group P2₁/n with four formula units in the unit cell. Dependent on the counterion, [AsF₆]^– or [GeF₆]^2–, considerable structural differences of the [ClSO₂NH₃]⁺ cation are observed. Furthermore, the hitherto unknown X‐ray single crystal structure of chlorosulfonamide is determined in the course of this study. Chlorosulfonamide crystallizes in the orthorhombic space group Pmc2 with four formula units per unit cell.     

Comparative toxicity of [3]ferrocenophane and ferrocene moieties on breast cancer cells

Recent results suggest that [3]ferrocenophane may be an interesting motif in the development of cytotoxic anti-cancer agents. We here report the synthesis of three such compounds based on the 1-[(p-R-phenyl)-phenyl-methylidenyl)]-[3]ferrocenophane skeleton with R = OH, NH₂ and NHC(O)CH₃ substitution on one of the phenyl rings. Cytotoxicity studies show that these compounds are up to four times more powerful against hormone-independent breast cancer cells than their corresponding ferrocene analogs.     

Synthesis and reactivity of enantiomerically pure N-alkyl-2-alkenyl azetidinium salts

A synthesis of stereodefined enantiomerically pure 2-alkenyl azetidines is described using Wittig olefination as key step. The quaternary triflate ammonium salts of these heterocycles were prepared in a stereoselective way and treatment of these azetidinium salts with a base (KHMDS or PhLi) induced a regioselective Stevens rearrangement leading to a 3-alkenyl pyrrolidine. An unprecedented S_N2′ reaction involving phenyllithium as nucleophile and an ammonium as leaving group was observed in one case.     

2-Phospha[3]ferrocenophanes with planar chirality: synthesis and use in enantioselective organocatalytic [3 + 2] cyclizations

Planar chiral phosphines displaying a new ferrocenophane scaffold have been prepared via a stereoselective approach. The P-cyclohexyl substituted phosphine affords high levels of asymmetric induction in the organocatalytic [3 + 2] annulation reaction between allenes and electron-poor olefins.     

Enantioselective reductions of [m] ferrocenophanones

Enantioselective reductions of prochiral ferrocenophane ketones were investigated. Oxazaborolidine mediated reduction led to corresponding chiral alcohols generally in good yields and enantioselectivities up to 97% ee. Ruthenium-catalyzed transfer hydrogenation was rather unsuccessful in reducing cyclic ferrocene ketones. Proline-derived activator together with trichlorosilane also proved to be an effective method for some substrates (up to 99% ee). Pronounced tendency of α-ferrocenyl ketones toward reductive deoxygenation was studied by DFT computational methods.