Molecular structure and electrochemistry of carbon-bridged diferrocenyl compounds

Four diferrocenyl compounds: FcC(CH₃)₂Fc (1), Fc(CH₃)C(C₂H₅)Fc (2), Fc(CH₃)C(C₃H₇)Fc (3), and Fc(CH₃)C(C₆H₅)Fc (4) were synthesized and characterized by NMR, FT-IR, MS, and elemental analysis. The molecular structures were determined by using X-ray single crystal diffraction. The electrochemical interactions between two ferrocenyl units in these compounds were investigated by cyclic voltammetry and theoretical calculation. The electron density of bridging carbon was a key factor for the separation of two ferrocenyl units.     

双二茂铁基吡咯衍生物电荷交互通道

以二茂铁炔烃为原料通过“一锅法”环加成反应合成了一系列2,5-双二茂铁基-1-苯基-吡咯衍生物, 包括: 2,5-双二茂铁基-1-(3-三氟甲基苯基)-吡咯(1), 2,5-双二茂铁基-1-(4-氟苯基)-吡咯(2), 2,5-双二茂铁基-1-苯基-吡咯(3), 2,5-双二茂铁基-1-(4-乙基苯基)-吡咯(4)和2,5-双二茂铁基-1-(4-乙氧基苯基)-吡咯(5), 使用元素分析, 傅里叶变换红外(FTIR)光谱, 质谱(MS)和核磁共振(NMR)等手段对化合物进行了结构表征. 采用循环伏安法(CV), 密度泛函理论(DFT)模拟计算研究了苯基上取代基对双二茂铁间电荷交互的影响. 研究发现第一氧化电位(E_a1), 峰电位差(ΔE)与取代基的哈米特常数(σ), 吡咯¹H NMR的化学位移(δ), 吡咯N原子自然轨道(NBO)电荷之间存在显著线性关联; 同时发现, N原子电荷密度升高, 双二茂铁间电荷交互能力减弱, N原子电荷密度降低, 双二茂铁间电荷交互能力提高. 因此这类双二茂铁基吡咯衍生物中N原子电荷密度对双二茂铁间电荷交互起着关键的影响作用.     

Influence of P‐Bonded Bulky Substituents on Electronic Interactions in Ferrocenyl‐Substituted Phospholes

2,5‐Diferrocenyl‐1‐Ar‐1H‐phospholes 3 a – e (Ar=phenyl ( a ), ferrocenyl ( b ), mesityl ( c ), 2,4,6‐triphenylphenyl ( d ), and 2,4,6‐tri‐tert‐butylphenyl ( e )) have been prepared by reactions of ArPH₂ ( 1 a – e ) with 1,4‐diferrocenyl butadiyne. Compounds 3 b – e have been structurally characterized by single‐crystal XRD analysis. Application of the sterically demanding 2,4,6‐tri‐tert‐butylphenyl group led to an increased flattening of the pyramidal phosphorus environment. The ferrocenyl units could be oxidized separately, with redox separations of 265 ( 3 b ), 295 ( 3 c ), 340 ( 3 d ), and 315 mV ( 3 e ) in [NnBu₄][B(C₆F₅)₄]; these values indicate substantial thermodynamic stability of the mixed‐valence radical cations. Monocationic [ 3 b ]⁺–[ 3 e ]⁺ show intervalence charge‐transfer absorptions between 4650 and 5050 cm^?1 of moderate intensity and half‐height bandwidth. Compounds 3 c – e with bulky, electron‐rich substituents reveal a significant increase in electronic interactions compared with less demanding groups in 3 a and 3 b .     

Ferrocene-decorated (phthalocyaninato)(porphyrinato) double- and triple-decker rare earth complexes: synthesis, structure, and electrochemical properties

A series of four mixed (phthalocyaninato)(porphyrinato) rare earth double-decker complexes (Pc)M[Por(Fc)(2)] [Pc = phthalocyaninate; Por(Fc)(2) = 5,15-di(ferrocenyl)-porphyrinate; M = Eu (1), Y (2), Ho (3), Lu (4)] and their europium(III) triple-decker counterpart (Pc)Eu(Pc)Eu[Por(Fc)(2)] (5), each with two ferrocenyl units at the meso-positions of their porphyrin ligands, have been designed and prepared. The double- and triple-decker complexes 1-5 were characterized by elemental analysis and various spectroscopic methods. The molecular structures of two double-deckers 1 and 4 were also determined by single-crystal X-ray diffraction analysis. Electrochemical studies of these novel sandwich complexes revealed two consecutive ferrocene-based one-electron oxidation waves, suggesting the effective electronic coupling between the two ferrocenyl units. Nevertheless, the separation between the two consecutive ferrocene-based oxidation waves increases from 1 to 4, along with the decrease of rare earth ionic radius, indicating the effect of rare earth size on tuning the coupling between the two ferrocenyl units. Furthermore, the splitting between the two ferrocene-based one-electron oxidations for triple-decker 5 is even smaller than that for 1, showing that the electronic interaction between the two ferrocene centers can also be tuned through changing the linking sandwich framework from double-decker to triple-decker. For further understanding of the electronic coupling between ferrocenyl groups, DFT calculation is carried out to clarify the electronic delocalization and the molecular orbital distribution in these double-decker complexes.     

Microwave‐assisted Synthesis,Characterization, and Density Functional Theory Study of Biologically Active Ferrocenyl Bis‐pyrazoline and Bis‐pyrimidine as Organometallic Macromolecules

Organometallic macromolecules such as ferrocenyl bis‐pyrazoline ( 2 , 3 ) and bis‐pyrimidine ( 4 , 5 ) derivatives were synthesized by reacting ferrocenyl bis‐chalcone 1 with thiosemicarbazide/phenylhydrazine/guanidine hydrochloride/thiourea, respectively, under microwave irradiation. Ferrocenyl bis‐chalcone 1 was synthesized by reacting acetyl ferrocene with terephthalaldehyde. Synthesized compounds were characterized by using IR, ¹H NMR, ¹³C NMR, EI‐MS, and elemental analysis. In vitro antibacterial activity against two Gram‐negative and two Gram‐positive bacteria was determined by the disc diffusion assay. Moreover, minimum inhibition concentrations were also measured with reference to chloramphenicol. Thioamide functionally containing ferrocenyl bis‐pyrazoline derivative 2 shows the best antibacterial activity on Escherichia coli and Salmonella typhimurium, among all tested compounds including the reference drug chloramphenicol. The structure–activity relationship is also developed by using computational calculations with density functional theory (DFT)/B3LYP method.     

二茂铁四唑和二茂铁甲醛缩3-取代丙二醇衍生物的合成

以甲酰基二茂铁6为原料, 通过与NH₄OH•HCl的缩合反应得到二茂铁肟7, 再经脱水剂脱水得到二茂铁腈8, 最后在(n-C₄H₉)₃SnCl的作用下与NaN₃反应生成新化合物二茂铁四唑(9). 以甲酰基二茂铁为原料, 在对甲苯磺酸(PTSA)的催化作用下与原甲酸三甲酯反应生成二甲基二茂铁缩醛(10), 然后与(R)-(－)-3-氯-1,2-丙二醇反应得到新的二茂铁缩醛衍生物12, 12再与NaN₃发生取代反应得到新的二茂铁缩醛衍生物13. 而新的二茂铁缩醛衍生物15的合成则是先由(R)-(－)-3-氯-1,2-丙二醇与CH₃OH在NaOH的作用下生成(R)-(－)-1-甲氧基-2,3-丙二醇(14), 再由14与二甲基二茂铁缩醛(10)反应得到的. 所合成的新化合物都用MS, ¹H NMR和IR谱确证了它们的结构.     

Synthesis and optical and electrochemical properties of glucose-cored ferrocenyl dendrimers

Triazole-based ferrocenyl glycoconjugates 1, 2, and 3 were synthesized by regiospecific copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) of azidoferrocenyl derivatives with glucose pentaacetylide. Higher generation ferrocenyl glycoconjugates form the stable ferrocenium cation and exhibit increased light harvesting property as revealed from cyclic voltammogram studies and ultraviolet–visible spectrum respectively due to the presence of more ferrocenyl and triazolyl units than the lower generation dendrimer.     

Comparison of structure,log<Emphasis Type="Italic">P</Emphasis> and P388 cytotoxicity of some phenyl and ferrocenyl cyclic chalcone analogues. Application of RP-TLC for log<Emphasis Type="Italic">P</Emphasis> determination of the ferrocenyl analogues

Cyclic chalcone analogues (2–5) and their ferrocenyl counterparts (6–10) were synthesized and their logP and P388 cyctotoxity were investigated. The structures of the newly synthesized compounds were confirmed by IR ¹H and ¹³NMR spectroscopy. Comparison of conjugation and stereochemistry of the respective derivatives showed similar characteristics compared to ones with some higher degree of conjugation in the ferrocenyl series. Comparison of logP of the ferrocenyl derivatives determined by a validated RP-TLC method showed the ferrocenyl derivatives to have higher logP _TLC. The results demonstrate that the differences in three dimensional shape, conjugation and lipophilicity do not have strong influence on the P388 cytotoxicity of the investigated phenyl (1−5) and ferrocenyl (6−10) enones.      

Mössbauer studies on ferrocene complexes: XI. Stabilisation and electron transfer in diferrocenyl monocations and related species

The structures of the diferrocenyl methyl cation (I) and protonated diferrocenyl ketone (II) are discussed in terms of modes of stabilisation. Evidence supporting the involvement of e₁ rather than e₂ orbitals in I is given with particular reference to values of Mössbauer quadrupole splittings (QS) which are very much smaller than those of monoferrocenyl carbenium ions. The reaction of Fc₂CO and Fc₂CHOH with FeCl₃ was investigated using frozen solutions. For Fc₂CO, a redox reaction occurred resulting in the oxidation of only one iron site even with excess oxidant. These results were confirmed by cyclic voltammetry. For Fc₂CHOH, no redox reaction was observed but the FeCl₃ appears to coordinate to the alcoholic oxygen atom resulting in a marked diminution of QS. The observed QS values are rationalised in terms of electron donation by the ferrocenyl e₁ orbitals. This explanation is extended to cover previously reported Mössbauer spectra for biferrocenium and biferrocenylenium monocations.     

Structural and Spectral Characterization of Two Charge-Transfer Salts Formed by Ferrocenyl and Polyoxometalate Units

Two charge-transfer (CT) salts based on the ferrocenyl cation CpFeCpCH₂N⁺(CH₃)₃ and Keggin-type anion [PW₁₂O₄₀]³⁻ or [SiMo₁₂O₄₀]⁴⁻ with the ratio of ferrocenyl:polyanion of 3:1 or 4:1, [CpFeCpCH₂N(CH₃)₃]₃[PW₁₂O₄₀] (1) and [CpFeCp-CH₂N⁺(CH₃)₃]₄[SiMo₁₂O₄₀] (2), were synthesized in high yields (68–71%) by traditional solution synthetic method and their structures were determined by X-ray diffraction analysis. The two salts both crystallize in triclinic space group P[`1] P\overline{1} and show the close interaction of the cyclopentadienyl ligand with the surface of the polyoxometalate. The UV–Vis diffuse reflectance spectra of 1 and 2 in the solid state indicate the presence of a new absorption band at λ _max = 550 and 630 nm, respectively, attributed to charge-transfer transitions between the ferrocenyl donors and the POM acceptors. The large difference of the shapes and positions of fluorescence emission bands of salts from the start materials also suggested the occurrence of a charge transfer process between the ferrocenyl cation and polyanion.     

Synthesis and crystal structure of an unexpected anionic trinuclear cobalt(III) complex with ferrocenyl-containing tridentate ONO donor Schiff base ligands

The tridentate ONO-donor Schiff base ligand derived from the condensation of 1-ferrocenyl-1,3-butanedione and 2-aminophenol, generated in situ and treated further with potassium tert-butoxide, reacted in THF with Co(NO₃)₂·6H₂O in the presence of pyridine to afford the ionic complex [{(η⁵-C₅H₅)Fe(η⁵-C₅H₄)-C(O)CH=C(CH₃)N-C₆H₄-2-O}₂Co(III)]^-[K(HOCH₂CH₃)₂]⁺ (1, 50% yield). Compound 1 was characterized by elemental analysis, FT-IR, and multidimensional ¹H and ¹³C NMR spectroscopy. Single-crystal X-ray diffraction reveals that the two metalloligands are meridionally coordinated to a Co(III) ion that adopts a slightly distorted octahedral geometry. The doubly solvated potassium counter-ion is asymmetrically positioned with respect to the two metalloligands. Such an arrangement allows the observation by ¹H NMR of restricted rotation of the ferrocenyl units and the splitting of both carbonyl and imine carbons, thus suggesting that the structure observed in the solid state is retained in solution. Complex 1 exhibits in its cyclic voltammetry curve two anodic reversible waves attributed to the oxidation of Co(III)-phenolates into Co(III)-phenoxyl radical and that of the ferrocenyl fragment into its ferrocenium counterpart.     

Charge-transfer hybrids containing covalently bonded polyoxometalates and ferrocenyl units

Two new charge-transfer hybrids with one or two ferrocenyl units covalently attached to a hexamolybdate cluster through an extended pi-conjugated bridge have been prepared using Pd-catalyzed coupling reactions on monoiodo- or diiodo-functionalized cluster substrates in over 60% yields. These hybrids have been characterized by (1)H NMR, FTIR, electrospray ionization mass spectrometry, and X-ray diffraction. The electronic spectra of these hybrids show a broad absorption tail extending beyond 550 nm, indicating the existence of charge-transfer transition from the ferrocenyl donor to the cluster acceptor. The observation of the clear charge-transfer transition indicates the contribution of charge-transfer resonance to the ground state in both 2a and 2b even though the donor-acceptor separation distance of 11.29 A is rather long, signaling a through-bond charge-transfer nature made possible by the organic pi-conjugated bridge. Cyclic voltammetry studies reveal a one-electron oxidation wave and a one-electron reduction wave for the hybrid with one ferrocenyl unit. For the one with two ferrocenyl units, a lower reduction potential and a two-electron oxidation wave are observed, indicating negligible electronic interactions between the two ferrocenyl units.     

Synthesis and Structure of an Enantiomerically Pure C2 Symmetric Ferrocenyl Carbene

The straightforward, high‐yield synthesis and X‐ray structural analysis of the air‐stable planar‐chiral bis(ferrocenyl)carbene 1,3‐bis‐{(1R)‐1‐[(1R)‐1‐(trimethylsilyl)ferrocen‐2‐yl]ethyl}imidazol‐2‐ylidene ( 5 ) is reported. Compound 5 is obtained in four steps from the amine [(1R)‐1‐(dimethylamino)ethyl]ferrocene ( 1 ) upon diastereoselective silylation, methylation, nucleophilic substitution by imidazole, and deprotonation. The X‐ray crystal structure of the free carbene shows the typical conformational features of the 1,2‐disubstituted ferrocenyl units, as found in other ferrocenyl ligands derived from 1 .     

A new series of dendrimers containing two ferrocenyl units and a Fréchet dendron around a triazine nucleus

The preparation and characterization of a new series of dendrimers containing two identical aminoferrocenyl units and a Fréchet dendron around a triazine nucleus is described. A sizable degree of electronic communication between the two redox active ferrocenyl residues was detected in dichloromethane solution containing tetrabutylammonium tetra(pentafluorophenyl)borate as the supporting electrolyte. Binding of glutarimide via hydrogen bonding interactions to all the dendrimers was easily detected by using (1)H NMR spectroscopic and voltammetric techniques.     

Theoretical and electrochemical studies on organometallic symmetrical schiff base complexes of Zn(II), Cu(II), Ni(II) and Co(II)

The electronic communication between two redox centres through a Schiff base complex has been investigated in a series of ethylenediimine-bis(1-ferrocenyl-1,3-butanedionate) complexes of Zn(II) 1, Cu(II) 2, Ni(II) 3 and Co(II) 4. Cyclic voltammetry experiments of 1 and 2 exhibit a unique two-electron reversible oxidation wave, whereas in the case of 3 and 4 two and three one-electron oxidation processes are, respectively, observed. These results suggest some electronic interaction between the iron atoms of the ferrocenyl groups. DFT calculations carried out on model complexes show that for all the studied compounds the removal of the first two electrons corresponds to the oxidation processes of the iron centres in the weakly coupled ferrocenyl termini. The electronic communication between the two iron centres increases on going from 1 to 4. Finally, a re-indexation of the bands observed in the UV-Visible spectra has been carried out using TDDFT calculations.     

Tunable electronic coupling in iron-chromium mixed-valence ions of methylated Cp-indene ligands

A series of heterobimetallic η⁶-[(ferrocenyl)indene]-Cr(CO)₃ complexes differing for the position of the ferrocenyl group, 1-(ferrocenyl)indene and 2-(ferrocenyl)indene, and the degree of indene methylation (tetramethyl- and hexamethyl-) have been prepared and studied with the aim to stabilise the mono- and dications generated by chemical and electrochemical oxidation, and at same time to tune the metal-metal electronic coupling in the mixed-valence cations. The magnitude of electronic delocalisation and spin density in the cations have been monitored by means of optical techniques (UV-Vis, near-IR, mid-IR) and EPR spectroscopy. The results have been rationalised in the framework of Marcus-Hush theory and at quantum chemistry level by DFT and TD-DFT methods, establishing that a metal-to-metal electronic coupling occurs the magnitude of which depends on the degree of indene methylation.     

Two new 1D cadmium(II) azido complexes: catina-Poly[di-μ1,1-azido(2,2′-bipyridyl)cadmium(II)] and a new polymorph of catina-Poly[di-μ1,1-azido (2-acetylpyridine)cadmium(II)]

Two new cadmium(II) azido complexes, [Cd(2,2′-bipy)(N₃)₂]_n (1) and [Cd(2-acpy)(N₃)₂]_n (2) (2,2′-bipy?=?2,2′-bipyridyl and 2-acpy?=?2-acetylpyridine), have been synthesized and structurally characterized by single-crystal X-ray diffraction methods. The coordination environment of the central cadmium atom is distorted octahedral (MN₆) in 1 and (MN₅O) in 2, with one-dimensional chains formed through Cd₂N₂ units and alternatively chelating N,N′-bipyridyl or N,O-2-acetylpyridine groups. The central Cd(II) ion is coordinated to two nitrogen atoms of a chelating bipyridyl group or one nitrogen atom and one acetyl oxygen of 2-acetylpyridine and four nitrogen atoms of four different end-on bridging (μ_1,1-N₃) groups. Chains in the c direction in 1 are stabilized in b direction by π–π interactions involving the aromatic rings of bipyridyl ligands. IR and NMR spectra of the two complexes are reported.     

Synthesis of dihydropyrazole‐bridged dinuclear ferrocenyl derivatives and their catalytic effect on thermal decomposition of ammonium perchlorate

Dihydropyrazole‐bridged dinuclear ferrocenyl derivatives (3a–3c) have been synthesized by the reaction of 1,3‐diferrocenyl‐2‐propen‐1‐on (1) with hydrazine, then acylation with acyl chloride directly. The structures were determined by mass spectrometry, IR and ¹H NMR spectroscopy. The compound 3c was characterized by single‐crystal X‐ray analyses. It was found that compounds 3a–3c have significant catalytic effect on the decomposition of ammonium perchlorate (AP). Compared with the thermal decomposition of pure AP, adding 3a, 3b and 3c in AP decreases its decomposition temperature by 78.8, 74.3 and 57.1 °C, respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

High Charge Delocalization and Conjugation in Oligofuran Molecular Wires

The extent of charge delocalization and of conjugation in oligofurans and oligothiophenes was studied by using mixed valence systems comprising oligofurans and oligothiophenes capped at both ends by ferrocenyl redox units. Using electrochemical, spectral, and computational tools, we find strong charge delocalization in ferrocene‐capped oligofurans which was stronger than in the corresponding oligothiophene systems. Spectroscopic studies suggest that the electronic coupling integral (H_ab) is roughly 30–50 % greater for oligofuran‐bridged systems, indicating better energy matching between ferrocene units and oligofurans. The distance decay constant (damping factor), β, is similar for oligofurans (0.066 A^?1) and oligothiophenes (0.070 A^?1), which suggests a similar extent of delocalization in the bridge, despite the higher HOMO–LUMO gap in oligofurans. Computational studies indicate a slightly larger extent of delocalization in furan‐bridged systems compared with thiophene‐bridged systems, which is consistent with oligofurans being significantly more rigid and less aromatic than oligothiophenes. High charge delocalization in oligofurans, combined with the previously reported strong fluorescence, high mobility, and high rigidity of oligofuran‐based materials makes them attractive candidates for organic electronic applications.