Unsubstituted Cyclopentadienyl Ring Research Articles

Supramolecular architectures in the salt trimethoprimium ferrocene-1-carboxylate and the cocrystal 4-amino-5-chloro-2,6-dimethylpyrimidine-ferrocene-1-carboxylic acid (1/1).

In the salt trimethoprimium ferrocenecarboxylate [systematic name: 2,4-diamino-5-(3,4,5-trimethoxybenzyl)pyrimidin-1-ium ferrocene-1-carboxylate], (C14H19N4O3)[Fe(C5H5)(C6H4O2)], (I), of the antibacterial compound trimethoprim, the carboxylate group interacts with the protonated aminopyrimidine group of trimethoprim via two N-H...O hydrogen bonds, generating a robust R22(8) ring motif (heterosynthon). However, in the cocrystal 4-amino-5-chloro-2,6-dimethylpyrimidine-ferrocene-1-carboxylic acid (1/1), [Fe(C5H5)(C6H5O2)]·C6H8ClN3, (II), the carboxyl-aminopyrimidine interaction [R22(8) motif] is absent. The carboxyl group interacts with the pyrimidine ring via a single O-H...N hydrogen bond. The pyrimidine rings, however, form base pairs via a pair of N-H...N hydrogen bonds, generating an R22(8) supramolecular homosynthon. In salt (I), the unsubstituted cyclopentadienyl ring is disordered over two positions, with a refined site-occupation ratio of 0.573 (10):0.427 (10). In this study, the two five-membered cyclopentadienyl (Cp) rings of ferrocene are in a staggered conformation, as is evident from the C...Cg...Cg...C pseudo-torsion angles, which are in the range 36.13-37.53° for (I) and 22.58-23.46° for (II). Regarding the Cp ring of the minor component in salt (I), the geometry of the ferrocene ring is in an eclipsed conformation, as is evident from the C...Cg...Cg...C pseudo-torsion angles, which are in the range 79.26-80.94°. Both crystal structures are further stabilized by weak π-π interactions.

Palladacycle from Cyclometalation of the Unsubstituted Cyclopentadienyl Ring in Ferrocene: Synthesis, Characterization, Theoretical Studies, and Application to Suzuki–Miyaura Reaction

The ferrocenylimines of general formula [(η5-C5H5)Fe(η5-C5H4)-CH2N═CH-C(R)═CH-C6H5] with R = H (2a) and CH3 (2b) were conveniently prepared from ferrocenylmethylamine. Reaction of 2a,b with lithium tetrachloropalladate in methanol in the presence of anhydrous sodium acetate resulted in the formation of the di-μ-chloro-bridged heteroannular cyclopalladated complexes 3a,b via the unsubstituted ferrocenyl C–H bond activation of the related ligands. Treatment of 3a,b with triphenylphosphine gave Pd{[(η5-C5H4)Fe(η5-C5H4)CH2N═CH-CH═CH-C6H5]}ClPPh3 (4a) and Pd{[(η5-C5H4)Fe(η5-C5H4)-CH2N═CH-C(CH3)═CH-C6H5]}ClPPh3 (4b), respectively. The crystal structures of 4a,b confirmed the formation of a carbon–palladium bond by using a carbon atom in the unsubstituted cyclopentadienyl ring. Additionally, theoretical studies using density functional theory calculations were carried out in order to account for the regioselectivity of cyclometalation. As for the catalysts, using 0.1% of palladacycles 4a,b in the presence of K3P...

(E)-1-Ferrocenyl-3-(2-meth-oxy-phen-yl)prop-2-en-1-one.

The structure of the title compound, [Fe(C5H5)(C15H13O2)], consists of a ferrocenyl moiety and a 2-meth­oxy­phenyl group linked through a prop-2-en-1-one spacer in an E conformation. In the ferrocene unit, the substituted cyclo­penta­dienyl (Cps) ring and the unsubstituted cyclo­penta­dienyl ring (Cp) are almost parallel to one another [dihedral angle = 1.78 (14)°], and the Cp and Cps rings are in a gauche conformation. The benzene ring is twisted by 10.02 (14) and 11.38 (11)° with respect to the Cp and Cps rings, respectively. In the crystal, mol­ecules are linked by weak C—H⋯O hydrogen bonds into supra­molecular chains running along the b-axis direction.

(E)-1-Ferrocenyl-3-(4-methoxyphenyl)prop-2-en-1-one

In the title compound, [Fe(C5H5)(C15H13O2)], a conjugated substituent group bridges a five-membered η5-C5H4 ring and a benzene ring. In the ferrocene unit, the substituted (Cps) and unsubstituted (Cp) cyclo­penta­dienyl rings are eclipsed and almost parallel [Cps—Fe—Cps angle = 176.1 (2)°]. The mol­ecule is linked into an S(5) motif via intra­molecular C—H⋯O hydrogen bonds. The mol­ecules are arranged into a three-dimensional framework by five inter­molecular C—H⋯O hydrogen bonds and one inter­molecular C—H⋯π(Cps) inter­action.

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.

Ferrocene compounds. XXXIX. 1-Ferrocenylisochromane.

In the title compound, [Fe(C(5)H(5))(C(14)H(13)O)], the plane of the heterocyclic ring is almost perpendicular to the plane of the substituted cyclopentadienyl ring, and the heterocyclic ring adopts a half-chair conformation. The conformation of the nearly parallel cyclopentadienyl (Cp) rings [the dihedral angle between their planes is 2.7 (1) degrees ] is almost halfway between eclipsed and staggered, and the rings are mutually twisted by about 19.4 (2) degrees (mean value). The mean lengths of the C-C bonds in the substituted and unsubstituted cyclopentadienyl ring are 1.420 (2) and 1.406 (3) A, respectively, and the Fe-C distances range from 2.029 (2) to 2.051 (2) A. The phenyl and unsubstituted cyclopentadienyl rings are involved in C-H.pi interactions, with intermolecular H.centroid distances of 2.85 and 3.14 A for C-H.pi(Ph), and 2.88 A for C-H.pi(Cp). In two of these interactions, the C-H bond points towards one of the ring bonds rather than towards the ring centroid. In the crystal structure, the C-H.pi interactions connect the molecules into a three-dimensional framework.

Synthesis of 1‘-Substituted Derivatives of 1,2,3,4,5-Pentaphenylferrocene

Pentaphenylferrocene was synthesized in 57% overall yield from 1-bromopentaphenylcyclopentadiene. Functionalization of the unsubstituted cyclopentadienyl ring using the Friedel−Crafts reaction gave 1‘-formyl- and 1‘-(2-chlorobenzoyl)-substituted derivatives. Hydrolysis of the latter provided the corresponding 1‘-carboxylic acid. This was readily transformed via a modified Curtius rearrangement into 1‘-amino-1,2,3,4,5-pentaphenylferrocene. This methodology also provided (η5-aminocyclopentadienyl)(η4-tetraphenylcyclobutadiene)cobalt and gave an improved synthesis of aminoferrocene.

Ferrocene-containing carbohydrate dendrimers.

Aliphatic amines, incorporating one or three (branched) acylated beta-D-glucopyranosyl residues, were coupled with the acid chloride of ferrocenecarboxylic acid and with the diacid chloride of 1,1'-ferrocenedicarboxylic acid to afford four dendrimer-type, carbohydrate-coated ferrocene derivatives in good yields (54-92%). Deprotection of the peracylated beta-D-glucopyranosyl residues was achieved quantitatively by using Zemplén conditions, affording four water-soluble ferrocene derivatives. When only one of the two cyclopentadienyl rings of the ferrocene unit is substituted, strong complexes are formed with beta-cyclodextrin in H2O, as demonstrated by liquid secondary ion mass spectrometry (LSIMS), 1H NMR spectroscopy, electrochemical measurements, and circular dichroism spectroscopy. Molecular dynamics calculations showed that the unsubstituted cyclopentadienyl ring is inserted through the cavity of the toroidal host in these complexes. The electrochemical behavior of the protected and deprotected ferrocene-containing dendrimers was investigated in acetonitrile and water, respectively. The diffusion coefficient decreases with increasing molecular weight of the compound. The potential for oxidation of the ferrocene core, the rate constant of heterogeneous electron transfer, and the rate constant for the energy-transfer reaction with the luminescent excited state of the [Ru(bpy)3]2+ complex (bpy = 2,2'-bipyridine) are strongly affected by the number (one or two) of substituents and by the number (one or three) of carbohydrate branches present in the substituents. These effects are assigned to shielding of the ferrocene core by the dendritic branches. Electrochemical evidence for the existence of different conformers for one of the dendrimers in aqueous solution was obtained.

Heterobimetallic (Ferrocenyl)indenyl Rhodium Complexes. Synthesis, Crystal Structure, and Oxidative Activation of [η5-(1-Ferrocenyl)indenyl]RhL2 [L2 = COD, NBD, (CO)2

The binuclear [η5-(1-ferrocenyl)indenyl]Rh(NBD) (1), [η5-(1-ferrocenyl)indenyl]Rh(COD) (1a), and [η5-(1-ferrocenyl)indenyl]Rh(CO)2 (2) complexes have been synthesized (NBD = norbornadiene; COD = cycloocta-1,5-diene). The crystal structure determination showed that the iron and rhodium nuclei are disposed in a transoid configuration in 1 probably to avoid steric repulsions. On the contrary, in 2 the metals are in a cisoid configuration due to the presence of stabilizing π-hydrogen bonds between the CO's and the hydrogens of the unsubstituted cyclopentadienyl ring. The results of the chemical and electrochemical oxidation of 2 are in favor of the existence of an effective interaction between the two metals.

Syntheses and Physical Properties of Ferrocene Derivatives (VIII) Crystal Structure of a Liquid Crystalline Ferrocene Derivative, ω-[4-(4-methoxyphenoxycarbonyl) phenoxycarbonyl]butyl 4-ferrocenylbenzoate

The structure of a monosubstituted ferrocene derivative of which the flexible spacer is located between the ferrocenyl and mesogenic groups, ω-[4-(4-methoxyphenoxycarbonyl)phenoxycarbonyl]butyl 4-ferrocenylbenzoate was determined by the X-ray diffraction method. The -C4H8- chain introduced as a flexible spacer is an all-trans conformation. The molecule is slightly bent around the ester group to the phenyl ferrocenyl group in order to form a rod-like structure. The molecular geometry is a rod-like feature, and two cyclopentadienyl rings exhibit an eclipsed conformation rather than a staggered one. As a result, this bent structure can lead to efficient packing because it is suitable to make up a bulk of unsubstituted cyclopentadienyl ring, and may play an important role in the appearance of the liquid crystal phase. The molecules are arranged in layers just like the smectic phase of the liquid crystals.

Selective synthesis of ferrocenes

We have developed a new one pot procedure for the selective functionalization of the 1′ position in ferrocenecarbaldehyde, with fair yields (up to 70%) and good regioselectivity (>90/10). Our method uses lithium N-methylpiperazide as a temporary protecting group of the aldehyde function and directing group for lithiation on the unsubstituted cyclopentadienyl ring of ferrocene. The extension of this new method with enantiomerically pure 2-substituted ferrocenecarbaldehydes provides an easy access to various enantiomerically pure 1,2,1′-trisubstituted ferrocenes with three different groups. Finally, when applying our method for the lithiation of 1,1′-ferrocenedicarbaldehyde with a chiral amine, we found a one pot synthesis of 1,2,1′,2′-tetrasubstituted C 2-symmetrical ferrocenes with very high enantiomeric excesses (>99%). Furthermore, changing the experimental conditions allows us to obtain 1,2,1′-trisubstituted ferrocenes with a very good enantioselectivity (up to 96%). The first chiral enantiomerically pure 2-substituted 1,1′-( β- oxa-trimethylene)ferrocenes and the first chiral enantiomerically pure C 2-symmetrical-disubstituted 1,1′-( β- oxa-trimethylene)ferrocene were also synthesized.

Redox potential and substituent effects in ferrocene derivatives: II

The anodic behavior of 31 ferrocene derivatives (FcX) (four of which have been prepared for the first time) of the types shown below has been investigated by cyclic voltammetry (and, in some cases, also by controlled-potential electrolysis and differential pulse polarography) at a Pt electrode, in an aprotic solvent: FcC(Y)Z (class A; Y  R (hydrogen, alkyl or unsaturated-carbon moiety) or Cl; Z  CRR′, derived functionalized groups or {W(CO) 5}); FcC(Y)O (class B; Y  R or OH); other types (class C, including azide, other unsaturated N moieties, acyloxy or phosphino); disubstituted ferrocenes (class D, with alkyl, aminoalkyl, phosphino, B(OH) 2 or −HGCl substituents, or the SSS bridge). All these substituted ferrocenes exhibit a one-electron reversible oxidation centered at iron and the effect of the substituents on the half-wave oxidation potential is discussed in terms of electronic properties. Using the accepted linear correlations between the half-wave oxidation potential and the Hammett constant σ p of the substituent, σ p was estimated for the first time for 29 of the substituents in the ferrocenes listed above. The anomalous behavior of complexes with a hydroxy or a carbonyl group is discussed. No correlation was observed between the oxidation potential and either the energy of the electronic absorption bands or the 1H NMR chemical shift of the unsubstituted cyclopentadienyl ring, although there are rough correlations for class A compounds. This behaviour is compared with those of [Fc-CHYZ]. kw]Iron; Redox potentials; Ferrocenes; Electrochemistry; Substituent effects

Structures of 1-ferrocenyl-1-phenylethanol, ferrocenyl(diphenyl)methanol and ferrocene-1,1'-diylbis(diphenylmethanol)

Racemic 1-ferrocenyl- 1-phenylethanol, [(CsHs)Fe- (CsHa)]CPhMeOH (I), crystallizes as discrete molecules which are not involved in hydrogen bondinog; the shortest intermolecular O-..O contact is 3.768(3) A and the hydroxyl H atom is orientated towards the unsubstituted cyclopentadienyl ring. Ferrocenyl(diphenyl)methanol, [(CsHs)Fe(CsHa)]CPh2OH (II) is hydrogen bonded to form centrosynunetric dimers with O...O 2.816(1) and H...O 2.52 ]k. Ferrocene-l,l~-diylbis(diphenylmeth - anol), Fe[(CsHa)C(Ph)2COH]2 (III) crystallizes as a dimeric aggregate with the Fe atoms on twofold crystallographic symmetry axes and the four O atoms defining a folded trapezium with O...O 2.762(2), 2.714(2) and 2.865(2) A,. The four hydroxyl groups are disordered equally over two orientations such that there are two halfoccupancy H-atom sites between each hydrogen-bonded oxygen pair.

Regiochemistry of acetylation of ferrocenylarylethylenes

We describe the synthesis and Friedel-Crafts acetylation of a series of ferrocenylarylethylenes, C 15 H 5 FeC 54 =CH(C 6 H 4 -p-X), where X = NO 2 (3a), Br (3B), and NME 2 (3c). Compounds 3a-c provide a direct comparison of the reactivity of ferrocene, olefin, and aryl functionlities. The regiochemistry of substitution of these compounds depends on the nature of the aryl functionalities. Acetylation occurs predominantly at the olefin and the unsubstituted cyclopentadienyl ring; substitution does not occur at the aryl or ar the substituted cyclopentadienyl ring

Acylation of ω-phenylalkanoylferrocenes by cinnamoyl and phenylpropiolyl chlorides

In Friedel-Crafts acylation of ω-phenylalkanoylferrocenes, the site of electrophilic attack depends on the reagent used. The acylation with cinnamoyl chloride yields preferentially the products of substitution of the unsubstituted cyclopentadienyl ring of ferrocene. The acylation with phenylpropionyl chloride affords the products of acylation of the benzene ring of the starting compound. The different behaviour of both acylating agents is discussed.

Self-Diffusion, Overall Rotation of Molecules, and Ring Motions in the Three Solid Phases of Formylferrocene, Fe(C5H5) (C5H4CHO), as Studied by 1H NMR and Differential Thermal Analysis

The temperature dependences of static and rotating frame 1H spin-lattice relaxation times, T1 and T1ϱ, respectively, and also of 1H spin-spin relaxation time, T*2 were studied for formylferrocene Fe(C5H5)(C5H4CHO). Broadline 1H NMR was investigated over a wide range of temperature. Differential thermal analysis revealed a new second-order phase transition at 294 K. At 77 K, formylferrocene was found to form a rigid lattice. Above 130 K, the onset of the Cs reorientation of the cyclopentadienyl ring in the molecule about its C5 axis was observed to take place with the average activation energy of 14.5 kJ mol−1. In the plastic phase above 317 K, the uniaxial as well as overall rotations and self-diffusion of the molecule as a whole were detected to occur. Other motional parameters of the unsubstituted cyclopentadienyl rings and the molecules in each phase were evaluated.

Mass spectrometry of π-complexes of transition metals : XX. Dimethylaminoalkyl derivatives of ferrocene and cymantrene; the determination of the distribution and the total content of deuterium label

The mass spectrometry behaviour of dimethylaminomethyl- and α-(dimethylamino)ethyl derivatives of cymantrene and ferrocene, their iodine methylates as well as of the deutero analogues of these compounds has been studied. It has been shown that mass spectrometry can be successfully employed for the quantitative determination of the total deuterium content in aminoalkyl derivatives of cymantrene and ferrocene, the distribution of the label between the dimethylaminoalkyl group and the metallocenyl fragment and in case of the dimethylaminomethylferrocene also between the substituted and unsubstituted cyclopentadienyl rings. The data on the distribution of the isotopic label were used to ascertain the mechanism of fragmentation of the dimethylaminomethylferrocene under electron impact.

ChemInform Abstract: ELECTROCHEMICAL PREPARATION OF ESTERS OF FERROCENYL‐CONTAINING CARBOXYLIC ACIDS

AbstractDurch Elektrolyse einer methanolischen Lösung von Ferrocen (II) und Oxalsäure (I) bei 15°C mit 25 Volt erhält man die Ferrocencarbonsäuremethylester (III) und (IV).

Rearrangements and hydrogen—deuterium exchange in ferrocenylcarbenium ions

The rearrangement of the t-butyl group in t-butylferrocenyl carbenium ions (VI) and the hydrogen—deuterium exchange in the methyl group of methylferrocenyl carbenium ions (XVI) has been studied. The reaction rates depend on the size of the substituents at the carbenium ion center, an increase in the size of the substituents causing an increase in the rate. This effect is attributed, on the basis of the Gleiter and Cais models of ferrocenyl substituted carbenium ions, to increased steric hindrance between the substituents and the unsubstituted cyclopentadienyl ring.

Electrophilic substitutions on some ferrocenyl analgues of chalcones an unusual reaction caused by the high stability of the α-ferrocenylmethyl carbenium ion

Friedel—Crafts acetylation of 5-ferrocenyl-1-phenyl-2,4-pentadie-1-one and 1-ferrocenyl-5-phenyl-1,4-pentadien-3-one has been acomplished. It was found that acetylation takes place on the unsubstituted cyclopentadienyl ring of ferrocene as well as on the double bond of chalcones. In the light of these results the Friedel—Crafts acetylation of 3-ferrocenyl-1-phenyl-2-propen-1-one was reinvestigated and the structures of some drivatives, described earlier, were corrected. The mechanism of the acetylation is discussed briefly. Friedel—Craft alkylation and electrophilic bromination of 3-ferrocenyl-1-phenyl-2-propen-1-one have also been attempted.