Synthesis and characterisation of water soluble ferrocenes: Molecular tuning of redox potentials

A range of novel water-soluble alkylated ferrocene sulfonate compounds are reported. Mono- and di-sulfonation on a series of alkyl ferrocenes produced 1,1′-dimethyl ferrocene sulfonate, 1,1′-dimethyl ferrocene disulfonate, 1,1′-diethyl ferrocene sulfonate, 1,1′-diethyl ferrocene disulfonate, t-butyl ferrocene sulfonate, t-butyl ferrocene disulfonate, ethyl ferrocene sulfonate, ethyl ferrocene disulfonate, n-butyl ferrocene sulfonate and n-butyl ferrocene disulfonate. All compounds were characterized by NMR spectroscopy, UV/Vis spectroscopy and electrochemical analysis. ¹H and ¹³C NMR studies have revealed the formation of several isomers with sulfonation occurring on positions α and β to the alkyl substituent or on the unsubstituted cyclopentadienyl ring. Variation of the alkyl group allowed the isomeric pattern to be tuned such that the final products followed either electronic or steric control. Cyclic voltammetry of the resulting products showed that the redox potential of the iron centre can be easily manipulated by changing the substituents on the cyclopentadienyl rings. This result has significant implications in the future development of homogenous redox mediators for sensing applications.     

The highly regiospecific synthesis and crystal structure determination of 1,1′-2,5′ substituted ring-locked ferrocenes

1,1′-Ferrocene biscarboxaldehyde (1) has been prepared and the aldehyde groups were subsequently protected with acetal groups to produce 1,1′-bisacetalferrocene (2). A ring-locked ferrocene was synthesised by further derivatisation of the cyclopentadiene rings at the 2,2′ positions with phosphine substituents to produce 2,2′-bis-(acetal)-1,1′-diphenylphosphinoferrocene (3), which was subsequently coordinated to either a nickel chloride (5) or nickel bromide (6) metal centre. The ring-locked ferrocene complexes produced 2,5′-bis-(acetal)-1,1′-diphenylphosphinoferrocene substitution patterns. The acetal protecting groups of 2,2′-bis-(acetal)-1,1′-diphenylphosphinoferrocene were removed to produce 1,1′-bis-carboxaldehyde-2,2′-diphenylphosphinoferrocene (4). The Cp rings of 1,1′-bisacetalferrocene were also further derivatised at the 2,2′ positions with a silane to produce the ring-locked 1,1′-siloxane-2,5′-bisacetalferrocenophane (7). The acetal protecting groups were removed from this to produce 1,1′-siloxane-2,5′-ferrocenophanecarboxaldehyde (8). For both the phosphine and siloxane electrophiles, the substitution on the Cp rings gives chiral products (obtained as racemic mixtures). Due to the highly regioselective nature of the reaction and diastereoselectivity in the products only C₂-symmetric compounds were observed without the presence of meso diastereoisomers. Subsequent ring-locking forced the Cp rings to rotate, leading to 1,1′-ring-locked ferrocenes with 2,5′-arrangement of the acetal groups (i.e. on opposite faces of the ferrocene unit).     

Synthesis, structures and reactions of some metallocene alcohols

E-1-Ferrocenyl-4,4-dimethylpent-2-ene-1-one has been synthesised from the Friedel-Crafts acylation of ferrocene with E-3-tert-butylacryloylchloride and converted to 1-ferrocenyl-3-chloro-4,4-dimethylpentan-1-one using ethereal hydrogen chloride. This new chloro ketone has been converted into three new ferrocene alcohols: 1-ferrocenyl-3,4-dimethyl-4-hydroxypentan-1-one, 1-ferrocenyl-3-chloro-4,4-dimethylpentan-1-ol, and 2,2,6,6-tetramethyl-3-ferrocenyl-5-chloroheptan-3-ol. A new dinuclear ferrocene derivative, E,E-2,2,9,9-tetramethyl-5,6-diferrocenyl-deca-3,7-diene, was isolated after treatment of 1-ferrocenyl-3-chloro-4,4-dimethylpentan-1-ol with acidic alumina; its structure was confirmed by X-ray crystallography, whilst electrochemistry revealed metal-metal interactions of similar magnitude to those seen for other 1,2-bis(ferrocenyl)ethane derivatives. Crystal structures have also been determined for 2,2,6,6-tetramethyl-3-ferrocenyl-5-chloroheptan-3-ol, rac-1-hydroxy[3]ferrocenophane, rac-1S,3S-1,3-diphenyl-1-hydroxy[3]ferrocenophane, and of rac-1,1^′-diphenyl-1,1^′-(1,1^′- ruthenocenediyl)dimethanol and show an intramolecular Cl?H-O hydrogen bond, a tetramer based on O?H-O hydrogen bonds, no hydrogen bonding, and a dimer with inter- and intramolecular O?H-O hydrogen bonds, respectively.     

Synthesis of a new bidentate ferrocenyl N-heterocyclic carbene ligand precursor and the palladium (II) complex trans-[PdCl2(CfcC)], where (CfcC) = 1,1′-di-tert-butyl-3,3′-(1,1′-dimethyleneferrocenyl)-diimidazol-2-ylidene

A new ferrocenyl-N-heterocyclic carbene ligand precursor 1,1′-bis[(1-tert-butylimidazolium)-3-methyl]ferrocene dichloride has been synthesised and structurally characterised. The imidazolium salt was readily deprotonated in situ with KN(SiMe₃)₂ and reacted with [PdCl₂ (cod)] to afford the structurally characterised palladium (II) complex trans-[PdCl₂(C^∧fc^∧C)], where (cod) = 1,5-cyclooctadiene and (C^∧fc^∧C) = 1,1′-di-tert-butyl-3,3′-(1,1′-dimethyleneferrocenyl)-diimidazol-2-ylidene.     

Structural characterization of a copper(II) complex containing oxidative cyclization of N-2-(4-picolyl)-N′-(4-methoxyphenyl)thiourea,new ligands of 4-picolylthiourea derivatives and the precursor molecular structure of oxidative cyclization of N-(2-pyridyl)-N′-(4-methoxyphenyl)thiourea

Three new compounds of aryl thiourea derivatives, namely N-2-(4-picolyl)-N′-(4-methoxyphenyl)thiourea (L1), N-2-(6-picolyl)-N′-(4-methoxyphenyl)thiourea (L2) and N-2-(4-picolyl)-N′-(4-nitrophenyl)thiourea (L3), and the new copper(II) complex [Cu(4PicTz4OMePh)(OAC)(EtOH)] (C1), as a result of oxidative cyclization of the ligand (L1), were synthesized. In addition, pure precursor (P1), as the product of the oxidative cyclization of N-(2-pyridyl)-N′-(4-methoxyphenyl)thiourea (L4), was isolated and characterized. Ligands (L1) and (L2) were characterized by ¹H and ¹³C NMR and single crystal X-ray analysis. ¹H NMR spectroscopy showed strong hydrogen bonding interactions between N′H-functionalities and the pyridine nitrogen atoms as well as weak intermolecular hydrogen bonding between the thione sulfur and the NH hydrogen. Structural studies of complex (C1) showed that the copper ion is five-coordinated with a square-pyramidal environment. The oxidative cyclization of ligand (L1) results in an anionic bidentate ligand in complex (C1). Both ligand (L1) and precursor (P1) crystallize as centrosymmetric dimers.     

Pronounced stabilisation of the ferrocenium state of ferrocenecarboxylic acid by salt bridge formation with a benzamidine

Salt bridge formation between ferrocenecarboxylic acid and an excess of a N,N^′-diethylsubstituted benzamidine leads to a −0.27 V shift in the half-wave potential of the ferrocene moiety, corresponding to a 26 kJ mol⁻¹ stabilisation of the ferrocenium state.     

Synthesis of mono and doubly alkynyl substituted ferrocene and its crystal engineering using -C-H···O supramolecular synthon

Mono and doubly alkynyl substituted ferrocene complexes, [Fc(CH₂OCH₂CCH)_n], 2-3 (2: n = 1; 3: n = 2; Fc = ferrocene) have been synthesized from the room temperature reaction of mono and 1,1′-dihydroxymethyl ferrocene, Fc(CH₂OH)_n , 1a-b (1a: n = 1; 1b: n = 2) and propargyl bromide, in modest to good yields. These new ferrocene derivatives have been characterized by mass, IR, ¹H, ¹³C NMR spectroscopy, and molecular structures of compound 2 and 3 were unequivocally established by single crystal X-ray diffraction study. The crystal structure analysis revealed that 2 and 3 consist of infinite 1D zig-zag hydrogen bonded chains and 2D microporous hydrogen bonded network of molecules, linked by intermolecular C-H···O hydrogen bonding. The molecular structures of both 2 and 3 are further stabilized by C-H···π interactions.     

Syntheses and studies of flexible amide ligands: a toolkit for studying metallo-supramolecular assemblies for anion binding

The syntheses of seven flexible bidentate bis-pyridyl diamide and four monodentate pyridyl amide ligands containing central amide units are described. The bis-pyridyl ligands were prepared in one step from commercially available compounds in moderate to good yield. These compounds all possess external metal coordinating pyridyl groups and internal amide functionalities, with the potential to bind anions. Crystal structures of six of the bis-pyridyl diamide ligands are described. The four compounds with xylene cores N,N′-[1,3-phenylenebis(methylene)]bis-3-pyridinecarboxamide 1, N,N′-[1,3-phenylenebis(methylene)]bis-4-pyridinecarboxamide 2, N,N′-[1,4-phenylenebis(methylene)]bis-3-pyridinecarboxamide 3 and N,N′-[1,4-phenylenebis(methylene)]bis-4-pyridinecarboxamide 4 crystallize with extensive amide N-H?OC hydrogen bonding between the diamide compounds, giving rise to two and three dimensional hydrogen bonded networks. N,N′-Bis(3-pyridylmethyl)benzene-1,3-dicarboxamide 5, the only compound with the amide groups directly attached to a central benzene core, was not able to be crystallised. N,N′-2,6-Bis(3-pyridylmethyl)pyridine dicarboxamide 6 and N,N′-2,6-bis(4-pyridylmethyl)pyridine dicarboxamide 7 have a mismatch of hydrogen bond donor and acceptor regions preventing ready involvement of the amide NH groups in network formation. For comparison we also prepared compounds N,N′-2′-propyl-6-(3-pyridylmethyl)pyridine dicarboxamide 10 and N,N′-2′-propyl-6-(4-pyridylmethyl)pyridine dicarboxamide 11 with two amide groups but only the one external donor pyridyl moiety, and compounds N-6-[(3-pyridylmethylamino)carbonyl]-2-pyridinecarboxylic acid methyl ester 8 and N-6-[(4-pyridylmethylamino)carbonyl]-2-pyridinecarboxylic acid methyl ester 9, which have only the one amide.     

Synthesis, NMR, IR spectroscopic and X-ray study of novel [pyridazin-3(2H)-one-6-yl]ferrocenes and related ferrocenophane derivatives. Study on ferrocenes. Part 14

On treatment with glyoxylic acid and hydrazine hydrate, 1,1′-diacetylferrocene was converted into the separable mixture of 1,1′-bis [pyridazin-3(2H)-one-6-yl]ferrocene and the hydrazone as well as the azine of 1-acetyl-1′-[pyridazin-3(2H)-one-6-yl]ferrocene. Successful cyclizations of 1,1′-bis[pyridazin-3(2H)-one-6-yl]ferrocene resulting in a series of novel ferrocenophanes containing heterocyclic units were performed under phase transfer- and homogeneous catalytic (RCM) conditions by the application of versatile dialkylating agents and second generation Grubbs’ catalyst, respectively. The structures were determined by mass spectrometry, IR, ¹H and ¹³C NMR spectroscopy including 2D-COSY, HMQC and HMBC measurements. The solid phase structure of a dimer product with π-stacking interaction was revealed by X-ray analysis.     

Chiral ferrocene cyanohydrin derivatives—access to novel intermolecularly linked and intramolecularly bridged ferrocene derivatives

By reduction of the cyano group in (R)-(cyanohydroxymethyl)ferrocene and (R,R)-1,1′-bis(cyanohydroxymethyl)ferrocene, amines were obtained giving access to several new diamine and diamide bridged chiral ferrocene derivatives. As a representative for an intramolecularly bridged ferrocene compound bearing two chiral centres (R,R)-8 was obtained with excellent optical purity.     

Synthesis and electrochemistry of 1,1′-bis(phosphino)cobaltocenium compounds

The electrochemistry of 1,1′-bis(diphenylphosphino)cobaltocenium hexafluorophosphate ([dppc][PF₆]), 1,1′-bis(dicyclohexylphosphino)cobaltocenium hexafluorophosphate ([dcpc][PF₆]), 1,1′-bis(di-iso-propylphosphino)cobaltocenium hexafluorophosphate ([dippc][PF₆]), and 1-(di-tert-butylphosphino)cobaltocenium hexafluorophosphate ([1-dtbpc][PF₆]) was examined in methylene chloride with tetrabutylammonium hexafluorophosphate as the supporting electrolyte. A reversible reductive wave followed by an irreversible wave at more negative potentials was observed. Ten new phosphinothioyl ([dppcS₂][PF₆], [dcpcS₂][PF₆], [dippcS₂][PF₆], [1-dtbpcS][PF₆], and 1,1′-bis(dicyclohexylphosphinothioyl)ferrocene) and phosphinoselenoyl derivatives ([dppcSe₂][PF₆], [dcpcSe₂][PF₆], [dippcSe₂][PF₆], [1-dtbpcSe][PF₆], and 1,1′-bis(dicyclohexylphosphinoselenoyl)ferrocene) were prepared and characterized, and the structures of eight of these compounds were determined. The electrochemistry of these phosphinochalcogenyl cobaltocenium compounds, as well as the previously prepared [dppcO₂][PF₆], displayed two reversible reductive waves at potentials less negative than that of the free phosphines. A correlation was found to exist between the Hammett substituent constant σ_p and the reduction potentials of these compounds. In addition, the phosphinoselenoyl [dppcSe₂][PF₆], [dcpcSe₂][PF₆], and [dippcSe₂][PF₆] displayed an electrochemically irreversible oxidative wave, potentially indicating an intramolecular Se-Se bonded trication. The electrochemistry of three new and five previously reported transition metal complexes of the general formula [M_nCl₂(P^∩P)][PF₆] (M = Pd or Pt, n = 1, P^∩P = dppc, dcpc or dippc; M = Au, n = 2, P^∩P = dppc or dcpc)) was also examined displaying at least two reductive waves at potentials less negative than that of the free phosphines. Comparison of the electrochemical data with that previously obtained for analogous ferrocenes indicates that a correlation exists between the reduction potentials of the cobaltocenium phosphines and the potentials at which oxidation of the ferrocene phosphines occurs. In addition, the structure of [Au₂Cl₂(dppc)][PF₆] was determined.     

1,1-(1-Propene-1,3-diyl)-ferrocene: modified synthesis, crystal structure, and polymerisation behaviour

The dehydro[3](1,1^′)ferrocenophanes, 1,1^′-(1-propene-1,3-diyl)-ferrocene (3a), and 1,1^′-(3-phenyl-1-propene-1,3-diyl)-ferrocene (3b) were synthesised under Shapiro conditions from the tosylhydrazones of the corresponding α-oxo-[3](1,1^′)ferrocenophanes. Electrochemistry shows 3a is oxidised at smilar potential to ferrocene; according 3a can be chemically oxidised using silver trifluoromethanesulfonate. The structure of 3a shows a ring tilt of 11.3°. Attempts to polymerise 3a using the ROMP initiator Mo(CHCMe₂Ph)[N(2,6-ⁱPr₂C₆H₃)][OCMe(CF₃)₂]₂ led to a mixture of insoluble material and a soluble mixture of apparently cyclic oligomers ([3a]_n).     

Synthesis, structural characterization and electrochemical study of 1,1′-ferrocenylene labeled amino acids

Unsymmetrical 1,1′-disubstituted ferrocenes bearing an amino acid moiety and a conjugated electron density controlling substituent were synthesized conveniently starting from 1,1′-ferrocenedicarbaldehyde. The novel ferrocene amino acid derivatives were completely characterized from their MS, ¹H NMR and ¹³C NMR spectra. Their electrochemical behavior was studied by cyclic voltammetry. Their formal redox potentials E_f were slightly influenced by the nature of the amino acid and mainly by the kind of the ethenyl substituent. Furthermore all the (Z)-isomers exhibited a slight anodic shift compared with the corresponding (E)-isomers.     

Soluble and thermally stable polyamides bearing 1,1′-thiobis(2-naphthoxy) groups

A new-type of sulfide containing diacid (1,1′-thiobis(2-naphthoxy acetic acid)) was synthesized from 2-naphthol in three steps. Reaction of 2-naphthol with sulfur dichloride afforded 1,1′-thiobis(2-naphthol) (TBN). 1,1′-Thiobis(2-naphthoxy acetic ester) (TBNAE) was successfully synthesized by refluxing the TBN with methylcholoroacetate in the presence of potassium carbonate. The related diacid was synthesized by basic solution reduction of TBNAE. The obtained diacid was fully characterized and used to prepare novel thermally stable poly(sulfide ether amide)s via polyphosphorylation reaction with different aromatic diamines. The properties of these new polyamides were investigated and compared with similar polyamides. These polyamides showed inherent viscosities in the range of 0.39-0.87 dL g⁻¹ in N,N-dimethylacetamide (DMAc) at 30 °C and at a concentration of 0.5 g dL⁻¹. All the polyamides were readily soluble in a variety of polar solvents such as DMAc and tetrahydrofuran (THF). These polyamides showed glass transition temperature (T_g) between 241-268 °C. Thermogravimetric analysis measurement revealed the decomposition temperature at 10% weight loss (T₁₀) ranging from 441- 479 °C in argon atmosphere.     

A robust dimethylgold(III) complex stabilized by a 2-pyridyl-2-pyrrolide ligand

Reaction of isopropyl[(2-pyridyl)alkyl]amines such as N-isopropyl-N-2-methylpyridine or N-isopropyl-N-2-ethylpyridine with aqueous solutions of NaAuCl₄ led to the formation of [LAuCl₂][AuCl₄] in low yields, where L = pyridyl amine bound to gold in a bidentate fashion. Reaction of 2-(3,5-diphenyl-1H-pyrrol-2-yl)pyridine with aqueous NaAuCl₄, however, proceeded with formal loss of HCl and direct formation of the gold(III) amido complex L′AuCl₂, where L′ = deprotonated pyrrolyl ligand. Optimization of the reaction conditions to make the new amido complex identified MeCN:H₂O (1:2) as the best choice of solvent, affording product in 92% yield. This dichloro amido complex is a convenient precursor to L′AuMe₂, which was found to be air-stable and thermally robust.     

Luminescence and electroluminescence of bis (2-(benzimidazol-2-yl) quinolinato) zinc. Exciplex formation and energy transfer in mixed film of bis (2-(benzimidazol-2-yl) quinolinato) zinc and N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine

The absorption and emission properties of benzimidazol-2-yl-quinoline (BIQ) and bis (2-(benzimidazol-2-yl) quinolinato) zinc (ZnBIQ) a new emitter used for organic light emitting device (OLED) were reported. Exciplexes are observed for ZnBIQ with N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) system, in both electro- and photoluminescent processes. The identification of exciplex emission in co-evaporated and multi-layer ZnBIQ thin film was reported for the first time. The optical formation of the exciplex involves the excitation of a single molecule, followed by the relaxation of that exciton into a lower energy exciplex state. Both BIQ and ZnBIQ possess very high thermal stabilities and can be purified by subliming under the high vacuum condition. Devices consisting of ZnBIQ as the emitting layer have been fabricated, and the emission spectra of ZnBIQ-base devices gave a voltage-dependent spectrum, with the red emission observed (3-7 V), switching over to strong white emission as the bias was raised.     

Synthesis and characterization of porphyrin-ferrocene-fullerene triads

Novel porphyrin-fullerene systems linked by ferrocene and related model compounds were successfully synthesized and characterized. Conformationally flexible 1,1′-disubstituted ferrocene functioned as effective modulator of the conformation between porphyrin and fullerene, as ¹H NMR spectra indicated, the porphyrin and C₆₀ moieties in the triads showed gauche type conformation. The electrochemical and photophysical studies showed that there were considerable interactions between porphyrin and fullerene in the ground state due to intramolecular π-stacking of the these two chromophores, assisted by the ferrocence linker. Fluorescence lifetime measurements indicated there might be two different quenching processes occurring simultaneously (intersystem crossing and electron transfer).     

DFT study of the reaction sites of N,N′-substituted p-phenylenediamine antioxidants

The geometry of N,N′-diphenyl-p-phenylenediamine (DPPD), N-phenyl-N′-(1′-methylbenzyl)-p-phenylenediamine (SPPD), N-phenyl-N′-(1,3-dimethyl-butyl)-p-phenylenediamine (6PPD), N-phenyl-N′-isopropyl-p-phenylenediamine (IPPD), and N-(1-methyl-1-phenylethyl)-N′-phenyl-p-phenylenediamine (CPPD) as well as of their dehydrogenation products has been optimized at B3LYP/6-31G^∗ level of theory. Our results support the idea of formation of stable ketimine Ph-NC structures (instead of quinonediimine structures) during consecutive dehydrogenation of SPPD, 6PPD, and IPPD antioxidants despite the formation of tertiary carbon-centered radicals in the first dehydrogenation step is energetically preferred for SPPD only.     

Reaction of ferrocenecarboxylic acid with N,N-disubstituted carbodiimides: synthesis, spectroscopic and X-ray crystallographic analysis of N,N-disubstituted N-ferrocenoylureas and identification of a one-pot coupling reagent for the formation of ferrocenecarboxamides in a non-aqueous solvent

N,N^′-dicyclohexyl-N-ferrocenoylurea 2, N,N^′-diisopropyl-N-ferrocenoylurea 3, N,N^′-di-p-tolyl-N-ferrocenoylurea 4 and N,N^′-di-tert-butyl-N-ferrocenoylurea 5 were obtained by reaction of ferrocenecarboxylic acid 1 with N,N^′-dicyclohexylcarbodiimide (DCC), N,N^′-diisopropylcarbodiimide (DIC), N,N^′-di-p-tolylcarbodiimide 10 and N,N^′-di-tert-butylcarbodiimide 11, respectively. Both N-tert-butyl-N^′-ethyl-N-ferrocenoylurea 6 and N^′-tert-butyl-N-ethyl-N-ferrocenoylurea 7 were obtained by reaction of 1 with N-tert-butyl-N^′-ethylcarbodiimide 12. In all cases a small amount of ferrocenecarboxylic anhydride 8 was formed as a by-product. All compounds were characterized by ¹H NMR, ¹³C NMR, IR and MS. Single crystal X-ray structural analyses were made of 2, 3 and 4. From the consistent results, the reaction products of 1 with carbodiimides appear different from those proposed by some earlier workers. With N-(3-dimethylaminopropyl)-N^′-ethylcarbodiimidehydrochloride 9 ferrocenoylurea was not isolated, but the main product was rather 8. The suitability of 8 as acylation reagent was applied by using 9 to obtain N-(3-triethoxysilyl)-propylferrocenecarboxamide in a one-pot reaction from 1 and 3-(triethoxysilyl)-propylamine.