Arene Spacer Research Articles

Extended sulfonated bipyridine ligands targeting the para-selective borylation of arenes

Iridium-catalysed borylation of arenes is one of the most widely used metal-catalysed C–H activation processes to elaborate aromatic rings. Exercising catalyst control over regioselectivity of the C–H oxidative addition step remains an area of active research. In this paper we describe the synthesis of a selection of sulfonated bipyridine ligands in which there is an arene spacer between the sulfonate group and the bipyridine backbone. In comparison to our previous work which achieved meta-selective borylation and in which the sulfonated bipyridine bore no spacer, we hoped that these extended ligands may allow a larger macrocyclic transition state for C–H activation thus favouring the para-position. The synthesised ligands have been evaluated on a series of arenes bearing amides and quaternary ammonium salts at varying distances from the aromatic ring.

An Ultimate Stereocontrol in Supramolecular Photochirogenesis: Photocyclodimerization of 2-Anthracenecarboxylate Mediated by Sulfur-Linked β-Cyclodextrin Dimers.

Stereoisomeric β-cyclodextrin (CD) dimers linked with a sulfur atom or an arene spacer were designed to create a tethered dual CD capsule for precisely manipulating the regio- and enantioselectivities of the photocyclodimerization of 2-anthracenecarboxylate (AC) to four stereoisomeric classical 9,10:9',10'-cyclodimers and two nonclassical 5,8:9',10'-cyclodimers. Among the dimeric CD hosts prepared, exo-3-thia-β-CD dimer formed 1:1 and 1:2 host-guest complexes with AC in aqueous solutions, the former of which hindered but the latter facilitated the AC photocyclodimerization with regio- and enantioselectivities much higher than those obtained with native β-CD or the rest of the β-CD dimers. The stereochemical outcomes turned out to be highly sensitive to and hence critically manipulable by the linking position and configuration of the connected saccharide units and the linker length, as well as the external variants, such as temperature, pH, and added salt. Eventually, the photocyclodimerization of AC mediated by the dimeric β-CD host gave enantiopure syn-head-to-tail-9,10:9',10'-cyclodimer in 97-98% yield in a pH 5.1 buffer solution at 0.5 °C and also in an aqueous CsCl solution at -20 °C.

Upper Rim Bifunctional cone-Calix[4]arenes Based on a Ligated Metal Ion and a Guanidinium Unit as DNAase and RNAase Mimics.

The catalytic activity of an artificial phosphodiesterase that combines a ligated metal ion (Cu(II), Zn(II)) with a guanidinium unit connected by a 1,2-vicinal calix[4]arene spacer was investigated in the transesterification of RNA models HPNP and four diribonucleoside 3',5'-monophosphates. Comparison with previous data related to the 1,3-distal regioisomeric metal complexes confirms the superiority of the Cu(II) complexes over the Zn(II) analogs and shows that in the reactions of HPNP, GpU, and UpU, the catalytic efficiency depends very little on whether the substitution pattern is 1,2-vicinal or 1,3-distal. On the other hand, CpA turned out to be a good substrate for the Cu(II) complex of the 1,2-vicinal catalyst and a bad substrate for the corresponding 1,3-distal regioisomer, whereas the opposite holds for GpA. Extension of the investigation to the cleavage of the DNA model BNPP showed that both Zn(II) and Cu(II) complexes exhibit good catalytic efficiency, with a superiority of the 1,2-vicinal catalyst in both cases. The data reported in this work show that rate accelerations over background for the best catalyst-substrate combinations at 0.5 mM catalyst concentration are 3.6 × 10(5)-fold for HPNP, 1.1 × 10(6)-fold for BNPP, and range from 1.3 × 10(6)- to 1.3 × 10(7)-fold for diribonucleoside monophosphates.

ChemInform Abstract: Synthesis of Pentasubstituted Pyrroles via Catalyst‐Free Multicomponent Reactions.

A facile and versatile catalyst-free method for the preparation of a wide range of pentasubstituted pyrroles has been reported using four-component reactions of arylglyoxal monohydrate, β-keto esters, amines, and various cyclic 1,3-dicarbonyls under mild reaction conditions. Employing this methodology, pseudo seven-component reactions have also been achieved in the case of p-phenylenediamine to provide conjugated bispyrroles with arene spacers.

Synthesis of Pentasubstituted Pyrroles via Catalyst-Free Multicomponent Reactions

A facile and versatile catalyst-free method for the preparation of a wide range of pentasubstituted pyrroles has been reported using four-component reactions of arylglyoxal monohydrate, β-keto esters, amines, and various cyclic 1,3-dicarbonyls under mild reaction conditions. Employing this methodology, pseudo seven-component reactions have also been achieved in the case of <i>p</i>-phenylenediamine to provide conjugated bispyrroles with arene spacers.

Gold(I) Chloride Complexes of Polyphosphine Ligands with Electron-Rich Arene Spacer: Gold–Arene Interactions

The reactions of Au(tht)Cl (tht = tetrahydrothiophene) with the electron-rich-arene-spacer-containing polyphosphine ligands N,N′-bis((diphenylphosphino)methyl)benzene-1,4-diamine (Dpba), N,N′-bis((...

Aza-Crown Macrocycles as Chiral Solvating Agents for Mandelic Acid Derivatives

A series of new chiral macrocycles containing the trans-1,2-diaminocyclohexane (DACH) subunit and arene- and oligoethylene glycol-derived spacers has been prepared in enantiomerically pure form. Four of the macrocycles have been characterized by X-ray crystallography, which reveals a consistent mode of intramolecular N-H···N hydrogen bonding and conformational variations about the N-benzylic bonds. Most of the macrocycles were found to differentiate the enantiomers of mandelic acid (MA) by (1)H NMR spectroscopy in CDCl(3); within the series of macrocycles tested, enantiodiscrimination was promoted by (i) a meta-linkage geometry about the arene spacer, (ii) the presence of naphthalene- rather than phenylene-derived arene spacers, and (iii) increasing length of the oligoethylene glycol bridge. (1)H NMR titrations were performed with optically pure MA samples, and the data were fitted to a simultaneous 1:1 and 2:1 binding model, yielding estimates of 2:1 binding constants between some of the macrocycles and MA enantiomers. In several cases, NOESY spectra of the MA:macrocycle complexes show differential intramolecular correlations between protons adjacent to the amine and carboxylic acid groups of the macrocycles and MA enantiomers, respectively, thus demonstrating geometric differences between the diastereomeric intermolecular complexes. The three most effective macrocycles were employed as chiral solvating agents (CSAs) to determine the enantiomeric excess (ee) of 18 MA samples over a wide ee range and with very high accuracy (1% absolute error).

Synthesis, structural characterization and luminescent properties of a series of Cu(i) complexes based on polyphosphine ligands

A series of Cu(I) complexes with a [Cu(NN)(PP)](+) moiety, [Cu(phen)(pba)](BF(4)) (1a), [Cu(2)(phen)(2)(pbaa)](BF(4))(2) (2a), [Cu(2)(phen)(2)(pnaa)](BF(4))(2) (3a), [Cu(2)(phen)(2)(pbbaa)](BF(4))(2) (4a), [Cu(dmp)(pba)](BF(4)) (1b), [Cu(2)(dmp)(2)(pbaa)](BF(4))(2) (2b), [Cu(2)(dmp)(2)(pnaa)](BF(4))(2) (3b) and [Cu(2)(dmp)(2)(pbbaa)](BF(4))(2) (4b) (phen = 1,10-phenanthroline, dmp = 2,9-dimethyl-1,10-phenanthroline, pba = N,N-bis((diphenylphosphino)methyl)benzenamine, pbaa = N,N,N',N'-tetrakis((diphenylphosphino)methyl)benzene-1,4-diamine, pnaa = N,N,N',N'-tetrakis((diphenylphosphino)methyl)naphthalene-1,5-diamine and pbbaa = N,N,N',N'-tetrakis((diphenylphosphino)methyl)biphenyl-4,4'-diamine), were rationally designed and synthesized. These complexes were characterized by (1)H and (31)P NMR, electrospray mass spectrometry, elemental analysis and X-ray crystal structure analysis. Introduction of different central arene spacers (phenyl, naphthyl, biphenyl) into ligands, resulting in the size variation of these complexes, aims to tune the photophysical properties of the complexes. Each Cu(I) ion in these complexes adopts a distorted tetrahedral geometry constructed by the chelating diimine and phosphine groups. Intermolecular C-H···π and/or π···π interactions are involved in the solid states. The dmp-containing complex exhibits better emission relative to the corresponding phen complex due to the steric encumbrance of bulky alkyl groups. Furthermore, for complexes with identical diimine but different phosphine ligands, the tendency of increased emission lifetime as well as blue-shifted emission in the solid state follows with the decrease in size of complexes. Intermolecular C-H···π interactions have an influence on the final solid state photophysical properties through vibrationally relaxed non-radiative energy transfer in the excited state. Smaller-sized complexes show better photophysical properties due to less vibrationally relaxed behavior related to flexible C-H···π bonds. Nevertheless, the tendency for increased quantum yield and emission lifetime, as well as blue-shifted emission in dilute solution goes with the increase in size of complexes. The central arene ring (phenyl, naphthyl or biphenyl) has an influence on the final photophysical properties. The larger the π-conjugated extension of central arene ring is, the better the photophysical properties of complex are. The rigid and large-sized complex 3b, with a high quantum yield and long lifetime, is the best luminophore among these complexes.

Evidence for Dual Pathway in Through‐Space Singlet Energy Transfers in Flexible Cofacial Bisporphyrin Dyads

Flexible "pacman" scaffolds built upon a calix[4]arene platform bearing a [18]crown-6 ether and either two OH functions or two OPr groups at the lower rim have been used to generate donor-acceptor (D-A) dyads incorporating a zinc-porphyrin donor and a free-base porphyrin acceptor. Through-space singlet energy transfer (SET) in the D-A dyads was studied by time-resolved fluorescence spectroscopy. Although the effects of conformational changes are well documented when the chromophores switch from a non-cofacial to a cofacial arrangement, little is known about flexible pacman scaffolds in which the changes are limited to the distance between the chromophores. The known SET rates for reported, geometrically well-defined, rigid pacman D-A dyads were used as calibration to estimate the D-A distances in the flexible pacman dyads. Due to the flexibility of the calix[4]arene spacer, the D-A dyads adopt a "closed" or "open" geometry that is tuned by intramolecular hydrogen bonds (O--H...[18]crown-6 ether) and by solvent interactions. Changes in the SET rates between the open and closed geometries were surprisingly less dramatic than expected, and are explained by a dual SET pathway that is specific to the calix[4]arene platform. Time-resolved fluorescence studies support the hypothesis that, for the "open" conformer, the preferred through space SET pathway (i.e., at the shortest distance) is located within the calix[4]arene cavity through the cofacial phenyl groups. For the "closed" conformer, the preferred through space SET route is located between the zinc and free-base porphyrins.

Ground- and Excited-State Pinched Cone Equilibria in Calix[4]arenes Bearing Two Perylene Bisimide Dyes

We report on a series of bis-chromophoric compounds o2c, g2c, and r2c, afforded by linking two identical orange, green, or red perylene bisimide (PBI) units, respectively, through a calix[4]arene spacer unit. The PBI units are characterized by their increasing sterical demand from a planar conformation, which is orange (o) colored, via the slightly distorted greenish (g) colored form to the strongly distorted derivative, which is red (r) colored. An equilibrium between the two possible pinched cone conformations of the calix[4]arene unit is observed for all three compounds, with one conformation showing a π-stacked sandwich arrangement of the PBI units and the second revealing a nonstacked conformation. The amount of the π-stacked conformation in the equilibrium enhances upon decreasing the steric encumbering of the respective PBI unit as well as upon lowering the solvent polarity, thus increasing π−π interactions as well as electronic coupling between the PBI units. Accordingly, the presence of the π-sta...

様々な分野で応用可能な広範囲波長領域の光を吸収するスクアリリウム系機能性色素

Novel bis-squaraine dyes have been synthesized in which two squaraine moieties are conjuga-tively linked by a methine group, thiophene, oligothiophene or arene spacer. New unsymmetrical squarylium dyes have been also prepared by condensation of mono-substituted squaric acid (semi-squaraine acid) with heterocyclic compounds with active methyl group or arylamines. These dyes exhibit large and intense absorption in the near-infrared region, and the X-ray structural analyses of these dyes show a planar structure. Semi-squaraine acids are key precursors for the synthesis of unsymmetrical squarylium dyes, and exhibited their absorption maxima at the shorter wavelength. Applications of squarylium dyes to photoconductive materials, photovoltatic devices, biological and environmental analysis are described. A Ca2+ ion-induced allostreic assem-bling of the squarylium dimmer was confirming by ESI-MS measurement showing the formation of metallo supramolecular complexes, that is the H-aggregate composed of at least three units.

New Concepts for Regio‐ and Stereoselective Bis‐ and Triscyclopropanations of C60

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Unsymmetrical Calix[4]arene Bisporphyrin Pacman

[structure: see text] The synthesis of a Pacman heterobisporphyrin associating an octaethyl porphyrinatozinc (ZnOEP) energy donor and a triaryl porphyrinatozinc (ZntPP) energy acceptor around a calix[4]arene spacer is described. Contrary to previous symmetrical architectures, correlations between the chromophores in the unsymmetrical calixarene bisporphyrin Pacman scaffold can now be observed in ROESY experiments. Independent of the excitation wavelength, only the luminescence of the ZntPP moiety was observed corresponding to quenching of the OEP moiety's emission.

Electrochemically Triggered Open and Closed Pacman Bis-metalloporphyrins

A new type of very compact Pacman bis-porphyrin scaffold has been obtained in which a calix[4]arene spacer provides both cofacial preorganization and flexibility. Changes in the distance between the two tetrapyrrolic macrocycles can be triggered by electrochemistry, where closed and open conformers can be interconverted in a handclapping motion.

Electrochemical Properties of A Dual Porphyrin System with Marked Affinity toward DABCO

Electrochemical characterization was made of a dual porphyrin system built on a calix[4]arene spacer and that of a porphyrin monomer. The porphyrin dimer showed marked affinity toward 1,4-diazobicyclo[2.2.2]octane (DABCO) such as that of molecular tweezers and reacted strongly with large interactions in the ground state as indicated by electrochemical behavior. Compared to the monomeric porphyrin, the initial oxidation potentials for this dimer were significantly reduced and reoxidation occurred in two distinct redox steps.

New concepts for regio‐ and stereoselective bis‐ and triscyclopropanations of C60

The synthesis of isomerically multiple adducts of C(60) with a defined three-dimensional structure is still one of the most challenging tasks of exohedral fullerene chemistry. The inherent regioselectivity of successive additions of addends such as malonates to the fullerene's [6,6]-double bonds is only moderate. In most cases difficult-to-isolate mixtures of regioisomers are obtained. The regioselectivity can be significantly improved if multifunctional addends able to undergo two or more additions are allowed to react with C(60). Preorganization and minimization of strain energy within the addend skeleton reduce the number of sterically allowed addition patterns. Improved concepts for highly regio- and stereoselective bis- and triscyclopropanations of C(60) are described. Two examples of the bisadditions with complete regioselectivity leading to trans-2- and cis-2 are presented. Here, the two malonate binding sites are linked by rigid tetraphenylporphyrin and calix-[4]-arene spacers. Selective trisadditions were achieved with the easy-to-synthesize and easy-to-modify tripodal addends 5-7, where the malonates are held together by a focal aryl moiety. Another very elegant approach for bis- and trisadditions involves cyclo-[n]-alkylmalonates. Selection between addition patterns with and without rotational axes is possible by choosing the right combinations of the flexible alkyl chains connecting the malonates. If alkyl chains of identical lengths are used bis- and trisadducts such as 19-21 and 25 with rotational symmetry are formed with high regioselectivity. These addition patterns are avoided if cyclo-[n]-malonates containing alkyl chains of different lengths are employed. In this case adducts such as 26 and 27 with C(s)-symmetry are formed. The use of the chiral cyclo-[3]-malonate 28 allows for the regio- and stereoselective synthesis of the enantiomerically pure e,e,e-trisadducts 29 and 30 containing an inherently chiral addition pattern with C(3)-symmetry.

Synthesis and Binding Properties of Calix[4]arene Dual Porphyrin Conjugate: Tweezers for DABCO.

A dual porphyrin system built on a calix[4]arene spacer was prepared and the corresponding Zn(II) complex 4 showed a marked affinity for 1,4-diazobicyclo[2.2.2]octane (DABCO) as compared with other amines.

Synthesis and Binding Properties of Calix[4]Arene Dual Porphyrin Conjugate: Tweezers for DABCO

A dual porphyrin system built on a calix[4]arene spacer was prepared and the corresponding Zn(II) complex 4 showed a marked affinity for 1,4-diazobicyclo[2.2.2]octane (DABCO) as compared with other amines.

The first versatile synthetic approach to cofacial bis-porphyrins with calixarene spacers.

[structure: see text] A versatile stepwise synthetic approach to cofacial bis-porphyrin species with calix[4]arene spacers has been designed. The three examples described demonstrate that the method allows selection, in a tailor-made fashion, of the calix[4]arene conformation, the type of functionalization of the calixarene rims, and the anchoring point of the chromophores on the calix[4]arene spacer.