Ethynyl[2.2]paracyclophanes and 4-isocyano[2.2]paracyclophane as ligands in organometallic chemistry

An alternative synthesis of (±)-4-ethynyl[2.2]paracyclophane (PCPCCH) (5) and 4,16-diethynyl[2.2]paracyclophane (6) via the Corey-Fuchs reaction has been developed. The olefinic intermediate 4-dibromovinyl[2.2]paracyclophane (3) has been isolated and structurally characterized. The racemic terminal alkyne 5 was employed as starting material for assembling of a luminescent extended π-conjugated system containing a thiophene unit and for a catalytic bis-silylation reaction yielding the olefinic dithioether Z-PhSCH₂Me₂SiC(H)C(PCP)SiMe₂CH₂SPh (9). The dimetallatetrahedran [Co₂(CO)₆(μ-η²-PCP-CCH)] (10) has been prepared and its crystal structure determined by an X-ray diffraction analysis. Alkyne 5 has also been used for the preparation of the Pt(0) complex [Pt(PPh₃)₂(PCPCCH)] (11) and the heterodinuclear dimetallacyclopentenone [(OC)₂Fe{μC(O)C(PCP)C(H)}(μ-dppm)Pt(PPh₃)] (12). The synthesis and reactivity of 4-isocyano[2.2]paracyclophane (15) towards heterobimetallic iron-platinum and palladium-platinum complexes is also presented. Opening of the dative iron → platinum bond of [(OC)₄Fe(μ-dppm)PtCl₂] (16) occurred upon addition of 15 to a CH₂Cl₂ solution of 16 leading to [(OC)₄Fe{μ-dppm}PtCl₂(CNPCP)] (17). Treatment of [ClPd(μ-dppm)₂PtCl] (18) with isocyanide 15 in a 1:1 ratio affords the A-frame compound [ClPd(μ-dppm)₂(μ-CNPCP)PtCl] (19), resulting from formal insertion of 15 into the Pd-Pt bond. Addition of 2 equiv. of 15-18 leads to the ionic A-frame compound [ClPd(μ-dppm)₂(μ-CNPCP)Pt(CNPCP)]Cl (20).     

The first three aromatic tribromides of the [2.2]paracyclophane series

From the reaction mixtures in the uncatalyzed polybromination of [2.2]paracyclophane by the action of excess Br₂ in CCl₄, there have been found along with the known products — 4,15- and 4,16-dibromo[2.2]paracyclophanes — two new aromatic tribromides of this series, which have been isolated in pure form: 4,12,15- and 4,15,16-tribromo[2.2]paracyclophanes. Special experiments demonstrated that the mixtures of these tribromides are formed as a result of competitive monobromination of 4,15-dibromo[2.2]paracyclophane; the 4,15,16-tribromo[2.2]paracyclophane, together with still another newly isolated isomer of this series — 4,8,12-tribromo[2.2]paracyclophane — is formed as a result of competitive monobromination of 4,16-dibromo[2.2]paracyclophane. As an explanation of the features of the orienting effect of substituents in these competing reactions, a rule was proposed: On the conventional orientation (from the electronic point of view) of entry of the bromine atom into the substituted ring (para > ortho > meta), a steric limitation is imposed on its attack in the pseudo-gem-position, owing to the bulky bromine atom that is transannularly positioned above it in the neighboring aromatic ring. The structures of all of the tribromides were established on the basis of elemental analyses, mass spectrometry, and¹H NMR spectrometry (including PMR using the homonuclear Overhauser effect). The data obtained in this work indicate that the 4,12,15-tribromo[2.2]paracyclophane and 4,15,16-tribromo[2.2]paracyclophane are predecessors of the two tetrabromides previously obtained by Cram — 4,7,12,15- and 4,5,15,16-tetrabromo[2.2]paracyclophanes; and the 4,8,12-tribromo[2.2]paracyclophane is a possible predecessor of 4,8,12,16-tetrabromo[2.2]paracyclophane, which is unknown up to the present time.A. N. Nesmeyanov Institute of Heteroorganic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1837–1843, August, 1992.     

5-Nitro[2.2]paracyclophanepyran-6-one—building block for the synthesis of [2.2]paracyclophanes containing condensed benzofuran subunits

The 5-nitro[2.2]paracyclophanepyran-6-one 2 has been synthesized. DBN treatment of the Diels-Alder cycloadducts of 2 followed by DDQ oxidation unexpectedly led to [2.2]paracyclophanes containing a condensed benzofuran subunit.     

Synthesis of novel mono- and diaryl-substituted [2.2]paracyclophanes

The cross-coupling reactions of 4-bromo[2.2]paracyclophane withp-tolylmagnesium bromide in the presence of various palladium and nickel complexes have been studied. It was found that [1,1 -bis(diphenylphosphinoferrocene)]palladium dichloride (PdCl₂ · dppf) shows the highest catalitic activity in this reaction. A series of new mono- and diaryl [2.2]paracyclophane derivatives with various substituents in the arene ring have been synthesized using this catalyst. It was shown that it is possible to cross-couple organozinc [2.2]paracyclophane derivatives with aromatic bromides. The composition and structure of the compounds obtained have been established on the basis of elemental analysis and spectral data. Some correlations between the structure and spectral parameters of mono- and diarylsubstituted [2.2]paracyclophanes have been found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1081–1085, June, 1994.The present work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-5246).The authors wish to express their gratitude to Prof. N. A. Bumagin for his scientific interest and helpful discussions.     

Synthesis and structure of [2.2]paracyclophanes incorporating alkyne units in the extended linear chain

The novel [2.2]paracyclophanes 4-7 with an extended π-conjugation due to the presence of a linear arylethynyl chain have been synthesized by the Pd-catalyzed Sonogashira coupling reaction.     

Conformational rigidity and flexibility of the paracyclophane skeleton in substituted [2.2]paracyclophanes

The character of distortions of the paracyclophane skeleton in various substituted [2.2]paracyclophanes was analyzed based on X ray diffraction data. The rigidity of the skeleton is provided by ethylene bridges and flexibility of the benzene rings, which adopt a boat conformation. The flexibility of the skeleton is manifested in the displacement of the benzene rings with respect to each other and conformational changes of ethylene bridges. The changes in these characteristics are very sensitive to intra- and intermolecular steric factors and are indicative of the absence of strong specific stacking interactions between the be nzene rings. Precision X-ray diffraction study and quantum-chemical calculations for unsubstituted [2.2]paracyclophane and 4,7-benzoquinono[2.2]paracyclophane demonstrated that there are no attractive interactions between the benzene rings, and the electron density is localized predominantly on the outer surface of the rings. This fact can be considered as the cage molecular effect of the [2.2]paracyclophane skeleton.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1707–1732, September, 2004.     

Construction of benzene ring-layered polymers

A simple and novel approach for synthesizing the benzene ring-layered polymers using [2.2]paracyclophane and xanthene skeletons was demonstrated. Palladium-catalyzed polymerization of pseudo-p-diethynyl[2.2]paracyclophane 1, 2,7-di-tert-butyl-4,5-diiodo-9,9-dimethylxanthene 2, and ethynylferrocene 3 gave the corresponding polymers 4a-c, which composed of 7-30 face-to-face benzene rings by changing the feed ratio of 1-3.     

Synthesis and self-assembly of novel calix[4]arenocrowns: formation of calix[4]areno[2]catenanes

A series of novel calix[4]arenocrowns 1a-c were efficiently synthesized by a one-pot reaction of calix[4]monohydroquinone diacetate 5 with ditosylate 6 and its analogues in the presence of sodium hydroxide. It was found that the calix[4]arenocrowns could form stable pseudorotaxane-type complexes 2a-c with paraquat, and further self-assemble into calix[4]areno[2]catenanes 3a-c with dicationic salt 8 and p-bis(bromomethyl)benzene.     

Unexpected chlorination of angularly annelated [2.2]paracyclophanes during DDQ oxidation

DDQ treatment of the Diels-Alder products 1 unexpectedly led to chloroderivatives 2. Chlorination did not occur during DDQ treatment of the fully aromatised compounds 3. These results point out that DDQ acted as an oxidant and source of chlorine.     

Suzuki aryl cross-coupling chemistry using derivatives of 1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane

An exploration into the scope of Suzuki aryl cross-coupling chemistry using derivatives of 1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane is reported. The coupling of 4-iodo-1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane with various aryl boronic acids and boronic acid pinacol esters was successful, with the exception of very sterically demanding systems, such as mesityl. The synthesis of the previously unreported 1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophanyl-4-boronic acid is described, together with various Suzuki aryl cross-coupling reactions of this new system. Using standard Suzuki methodology, it was possible to prepare dicyclophanes bearing two octafluoro[2.2]paracyclophane units separated by both one and two benzene rings.     

Synthesis of novel planar-chiral [2.2]paracyclophane derivatives as potential ligands for asymmetric catalysis

The synthesis of a variety of new 4,5-disubstituted [2.2]paracyclophane derivatives has been achieved employing different cross-coupling reactions. By this methodology, a heteroatom-variation of successful catalyst ligands was achieved, giving rise to a modular ligand system. The X-ray structure of 4-hydroxy-5-(1′-hydroxy-1′-phenylethyl)-[2.2]paracyclophane was determined to elucidate the configuration. Additionally, a diastereoselective synthesis of planar- and central-chiral 4-([2.2]paracyclophanyl)ethylamine was achieved, thus resulting in a planar- and central-chiral phenyl ethylamine analogue.     

Theoretical investigation of [2.2]paracyclophane as a donor toward a Cr(CO)3 group

A comparative molecular orbital study of [2.2]paracyclophane and simple arenes as ligands toward a Cr(CO)₃ group was performed with the aim of accounting for the observed coordination patterns. While the inter-ring repulsion is an important factor in [2.2]paracyclophane activation, it is not the only one. The molecular orbitals of two arene rings stacked parallel to each other were analyzed in some detail. The inward hybridization (toward the other ring) of the (arene)₂ HOMO was shown to reduce the strength of consequent bonding with the Cr(CO)₃ is fragment. The overall stabilization of [2.2]paracyclophane complex with Cr(CO)₃ is enhanced by a reduction of the inter-ring repulsion and strengthening of the Ar−Cr bond, and reduced by weakening of the intra-ring carbon-carbon bonds. The inter-ring repulsion increases with approach of the arenes to each other, as appears to happen in the structure of [2.2]paracyclophane complex with Cr(CO)₃. This explains the high donor ability of the free ring of the (arene)₂Cr(CO)₃ complex toward another Cr(CO)₃ fragment. It was proposed that the stabilization of the [2.2]paracyclophane complex with Cr(CO)₃ results ultimately from the relaxation of the strained framework of [2.2]paracyclophane. The kinetic factor in Cr(CO)₃ complexation was also studied by analyzing the charges on competing arene rings in monoaryl-substituted derivatives of [2.2]paracyclophanes. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 151–157, January, 1998.     

Dyes for sensitized solar cells by using [2.2]paracyclophane as a bridging unit

Organic dyes that consist of a [2.2]paracyclophane moiety between a triphenylamine donor group and a cyanoacrylic acid acceptor group have exhibited considerably high values of open-circuit voltage (V_oc) in the range of 0.69–0.74 V. In an experiment that involved using an ion liquid electrolyte (E2 electrolyte), the values of V_oc were increased to 0.03–0.04 V because of a decrease in the concentration of LiI. A typical device demonstrated a maximal incident photon-to-current conversion efficiency (IPCE) of 60% in the region of 350–475 nm, a short-circuit photo current density (J_sc) of 8.80 mA cm⁻², an open-circuit photovoltage (V_oc) of 0.74 V, and a fill factor (FF) of 0.65, corresponding to an overall conversion efficiency of 4.24% of CPG2b. The photophysical properties were analyzed using a time-dependent density functional theory (TDDFT) model with the M062X functional.     

Synthesis of [2.2]paracyclophane-pseudo-ortho-dicarboxylic acid

An efficient three-step synthesis of [2.2]paracyclophane-pseudo-ortho-dicarboxylic acid by dibromination of [2.2]paracyclophane, thermal isomerization of the resultingpseudopara-dibromide topseudo-ortho-isomer, followed by lithiation/carboxylation was developed. The possibility of preparation of two other novelpseudo-ortho-disubstituted carbonyl derivatives, 4-carboxy-12-(1-oxopenthyl)-[2.2]paracyclophane and di(4-carboxy[2.2]paracyclophanyl-12)ketone, was demonstrated when an excess of lithiation reagent (4 or 10 eq.) was used in the final step. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2001–2004, November, 1997.     

Stereoselective synthesis of homoallylic alcohols of the [2.2]paracyclophane series and their use as auxiliaries in asymmetric allylboration of aldehydes

Stereoselectivity of allylboration of 4-formyl[2.2]paracyclophane, 4-acetyl[2.2]paracyclophane, and 4-hydroxy-5-formyl[2.2]paracyclophane was studied and the relative configurations of the homoallylic alcohols obtained were established. Optically pure (Sp,Sc)-(+)-4-(4-hydroxy-1-methylbut-3-enyl)[2.2]paracyclophane and (Rc,Sc)-(+)-4-hydroxy-5-(4-hydroxybut-3-enyl)[2.2]paracyclophane were synthesized. The possibility of using (Sp,Sc)-(+)-4-(4-hydroxy-4-methylbut-3-enyl)[2.2]paracyclophane as a recoverable chiral auxiliary in asymmetric allylboration of aldehydes was demonstrated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 914–921, May, 2000.     

Design and synthesis of novel rhodamine-based chemodosimeters derived from [2.2]paracyclophane and their application in detection of Hg2+ion

For a better insight into the spectroscopic properties of [2.2]paracyclophane in fluorescent probes, a novel rhodamine-based chemodosimeter bearing [2.2]paracyclophane 4a has been designed and synthesized. The probe 4a exhibits a highly selective and sensitive response to Hg²⁺ over other transition metal ions in aqueous solution. Its detection limit is determined to be 77 nM. The significant changes in the fluorescence color could be used for the naked-eye detection. Furthermore, the probe 4a shows good membrane permeability and can be applied to detect intracellular Hg²⁺ in human lung adenocarcinoma cells (A549 cells). The crystal structure and spectral properties of its congener 4b that contains one 12-bromo [2.2]paracyclophane group and rhodamine moiety are also investigated for a comparison.     

Azobenzene-bridged calix[8]arenes

An azobenzene bridge was introduced into the lower (or smaller) rim of p-tert-butylcalix[8]arene (1) and 1,5-calix[8]crown-3 (2) to form 1,4-singly bridged (3) and 1,5:3,7-doubly bridged (4) calix[8]arene derivatives, respectively. Trans and cis isomers of conformationally rigid 4 were isolated. The quantum yields of the trans-cis photoisomerisation reactions have been measured.     

Calix[4]quinones. Part 4: The ClO2 oxidation of calix[4]arene dialkyl ethers

Except for the special case of calix[4]arene diethyl ether 1, the chlorine dioxide oxidation of dialkyl ethers 2-5 yielded only the corresponding calix[4]diquinone dialkyl ethers 8-11. Chlorine dioxide oxidation of calix[4]arene diethyl ether 1 produced two isomeric products 6 and 7, which were stable enough to be isolated by column chromatography. However, a slow conformational interconversion between isomeric pair 6 and 7 was observed at room temperature, and the equilibrium was reached after 400 h at 18 °C with an amount of 5:3 in favor of syn-isomer.     

Synthesis of 1,1,9,9-tetrafluoro[2.2]paracyclophane and its polymerization by vapor deposition method

1,1,9,9-Tetrafluoro[2.2]paracyclophane ( 1 ) was prepared successfully as white crystals in 72% yield via two-step reactions from 1,9-diketo[2.2]-paracyclophane. The polymerization of 1 by the vapor deposition method was carried out at pyrolysis temperature range of 400 to 800°C and deposition temperature range of ?20 to 20°C, and a tough, transparent poly(α,α-difluoro-p-xylylene) film was obtained in 72% yield at the pyrolysis temperature of 750°C and the deposition temperature of ?20°C. It was found that the pyrolysis of 1 gave a reactive α,α-difluoro-p-xylylene, which polymerized on the head-to-tail addition to give poly(α,α-difluoro-p-xylylene). Some properties such as solubility, thermal stability, glass transition temperature, and density for poly(α,α-difluoro-p-xylylene) were studied. © 1995 John Wiley & Sons, Inc.     

9,9-Dimethyl-8,10-dioxapentacyclo[5.3.0.0.0.0]decane and naphthotetracyclo[5.1.0.0.0]oct-3-ene: new substituted [1.1.1]propellanes as precursors to 1,2,3,4-tetrafunctionalized bicyclo[1.1.1]pentanes

Two new substituted [1.1.1]propellanes have been generated from the corresponding bicyclo[1.1.0]butanes in either single-step (1a) or four-step procedures (1b). The observed degree of double lithiation of the bicyclo[1.1.0]butanes is discussed in the context of DFT computational results. Addition reactions across the central C(1)-C(3) bonds of the propellanes were studied. Only the propellane 1b gave the biacetyl addition product.