Synthesis of π-extended porphyrins via intramolecular oxidative coupling

Porphyrins fused with other aromatic units at the meso- and β-positions have recently emerged as a hot topic of research. Their synthesis typically starts with preparation of precursors via either Suzuki coupling of a meso-bromoporphyrin or mixed-aldehyde condensation, and is followed by oxidative aromatic coupling, often using high-valent metal reagents (DDQ/Sc(OTf)(3) and Fe(iii) salts are among the most popular). In recent years, porphyrins were oxidatively coupled not only with well-known aromatic hydrocarbons such as naphthalene and pyrene, but also with more complex heterocyclic fragments, including indole, phenanthro[1,10,9,8-cdefg]carbazole and BODIPY. A subtle relationship exists between the output of intramolecular oxidative coupling and the nature of the second aromatic moiety, cation in the porphyrin cavity, oxidant, and type of remaining meso-substituent. The extension of the porphyrin chromophore leads to significant change in linear and non-linear optical properties. Very strong bathochromic shifts of absorption (λ(max) reaching 1.5-2 microns in some cases) and increases in two-photon absorption cross-sections are typical for these functional dyes.     

DNA-mediated electron transfer from a modified base to ethidium: π-stacking as a modulator of reactivity

Background: The DNA double helix is composed of an array of aromatic heterocyclic base pairs and, as a molecular π-stack, represents a novel system for studying long-range electron transfer. Because many base damage and repair processes result from electron-transfer reactions, the ability of DNA to mediate charge transport holds important biological implications. Seemingly contradictory conclusions have been drawn about electron transfer in DNA from the many different studies that have been carried out. These studies must be reconciled so that this phenomenon can be understood both at a fundamental level and in the context of biological systems.Results: The photoinduced oxidation of a modified base, 7-deazaguanine, has been examined as a function of distance, sequence, and base stacking in DNA duplexes covalently modified with ethidium. Over ethidium/deazaguanine separations of 6–27 Å, the photooxidation reaction proceeded on a subnanosecond time scale, and the quenching yield exhibited a shallow distance dependence. The efficiency of the reaction was highly sensitive to small changes in base composition. Moreover, the overall distance-dependence of the reaction is sensitive to sequence, despite the constancy of photoexcited ethidium as acceptor.Conclusions: The remarkable efficiency of deazaguanine photooxidation by intercalated ethidium over long distances provides new evidence for fast electron-transfer pathways through DNA. By varying sequence as well as reactant separation, this work provides the first experimental demonstration of the importance of reactant stacking in the modulation of long-range DNA-mediated electron transfer.     

Synthesis,molecular structure and reactivity of new π-conjugated diyne with ferrocenyl and phenyl units

New π-conjugated butadiynyl ligand FcC(CH₃)₂Fc′–CC–CC–Ph (L₁) has been synthesized and its reaction with Co₂(CO)₈ has been studied. New clusters [FcC(CH₃)₂Fc′–CC–CC–Ph][Co₂(CO)₆]_n [(1): n = 1; (2): n = 2] and [Fc–CC–CC–Ph][Co₂(CO)₆]_n [(3): n =  1; (4): n = 2] were obtained by the reaction of ligands FcC(CH₃)₂Fc′–CC–CC–Ph (L₁) and Fc–CC–CC–Ph (L₂) with Co₂(CO)₈ respectively and the composition and structure of the clusters and ligands have been characterized by elemental analysis, FTIR, ¹H and ¹³C NMR and MS. The crystal structures of compounds L₁, L₂, 2 and 4 have been determined by X-ray single crystal analysis.     

Synthesis of extended π-conjugated hypercrosslinked polymers via a Friedel–Crafts reaction and an intramolecular Scholl coupling reaction

Long-range conjugated structures are important for increasing the conductivity and broadening the application scope of hypercrosslinked polymers (HCPs). It is, however, difficult to fabricate long-range conjugated structures using conventional HCP synthesis methods. Herein, we report a simple and efficient strategy for the synthesis of HCPs with extended π-conjugated structures through Friedel–Crafts and intramolecular Scholl-coupling reactions from readily available aromatic compounds under mild conditions. Two conjugated HCPs (C-HCPs), namely, C-HCP-ATA and C-HCP-TPB, were prepared from anthracene (ATA) and triphenylbenzene (TPB), respectively, using this method. The proposed strategy not only ensures a high specific surface area of materials but also introduces a long-range conjugated structure into HCPs. The lithium-ion battery applications of the C-HCPs were investigated. As anode materials, C-HCP-ATA and C-HCP-TPB displayed higher lithium storage capacities, better conductivity, and higher stability than their precursors, HCP-ATA and HCP-TPB, which were prepared using the conventional method.     

PVC-silica hybrids: effect of sol–gel conditions on the morphology of silica particles and thermal mechanical properties of the hybrids

Hybrid materials from poly(vinyl chloride) (PVC) and silica have been prepared using different conditions by the sol–gel technique. In situ generation of silica network in the PVC matrix was carried out by hydrolysis/condensation of tetraethoxysilane (TEOS) in the matrix. Morphology of the silica particles produced in hybrid films was studied by scattering electron microscopy. The shape of silica particle produced in the matrix was modified by carrying out the sol–gel process under steam on the hybrid films using TEOS. The films were subjected to strain conditions during this process, which produced lamellar shaped particles in the matrix. It was possible to produce platelet type of structure with different aspect ratio by changing the composition and the stress conditions on the films during the steaming process. Addition of a very small amount of γ-glycidoxypropyltrimethoxysilane as compatibilizer drastically reduced the silica particles size in the matrix to nano-level. Thermal–mechanical properties of some of these hybrids were studied and related to the composition, structure and inter-phase interaction between the silica and the matrix.     

Quinoxaline-walled π-stacking molecules: synthesis,conformation, and luminescence properties

A series of semi-rigid N-phenylsuccinimides I (11Xy), N-arylmethylsuccinimides II (18Xy), and N,N′-(1,4-arylenebis(methylene))disuccinimides III (19XyX) walled by quinoxaline (QX), dimethylquinoxaline (diMQX), or benzoquinoxaline (BQX) ring were synthesized. Intramolecular π–π interactions in solution were detected by NMR and fluorescence spectroscopy, in terms of reciprocal anisotropic shielding and exciplex formation, respectively. The X-ray crystallographic analysis revealed the preferential conformations in solid state, which were compatible with the results of conformational studies by NMR and fluorescence spectroscopy. The results collectively indicated that 18Xy and 19XyX are driven by intramolecular π–π interactions in the mode of π-stacking (face-to-face) or T-shaped (edge-to-face) configuration to preferentially adopt the folded- and the double folded-conformation, respectively, where the spaced aromatic rings are oriented syn to each other in close proximity.     

Synthesis and intramolecular heterocyclization of β-amino ketone thiosemicarbazones

Intramolecular heterocyclization of thiosemicarbazones derived from saturated and conjugated β-amino ketones afforded previously unknown dihydro-1,3,4-thiadiazole derivatives. A probable scheme of the transformation of multicenter intermediate includes generation and intramolecular cyclization of a thiol thiosemicarbazone tautomer without participation of conjugated double carbon-carbon bond in the substrate.     

Closely stacked oligo(phenylene ethynylene)s: effect of π-stacking on the electronic properties of conjugated chromophores

In this work, a bicyclo[4.4.1]undecane scaffold is used to hold oligo(phenylene ethynylene) units in a cofacially stacked arrangement along the entire length of the conjugated units. We study the impact that the resulting strong interchain interactions have on the photophysical properties. The length of the individual oligomer branches was varied from three to five rings to investigate the effect of conjugation on the electronic properties of the stacked segments. Absorption and fluorescence spectra were recorded and compared to those of the corresponding unstacked analogues. Time-dependent density functional theory calculations were carried out and helped to rationalize the low-energy features present in the fluorescence spectra of the stacked systems. The calculations indicate that the low-energy emissions are due to the presence of excimer-like states. The stronger intensity of the low-energy fluorescence band observed in the five-ring stacked system compared to the three-ring analogue is attributed to the smaller activation barrier that separates the local intrachain state and the excimer-like state in the former compound.     

Synthesis and π-facially selective cycloadditions of pinofurans

The synthesis of the strained pinofuran (1) and methylpinofuran (2) was investigated by a number of approaches. The preferred route to 1 was via the monoprotected (Z)-enediol 8, which was obtained by Z-selective LiNEt₂-induced opening of the epoxide derived from protected homoallylic alcohol 3 (nopol). Methylpinofuran (2) was prepared from 1,4-diketone 14, which was obtained by a vinyl-Grignard 1,4-addition to pinocarvone (12) followed by ozonolysis. Pinofurans 1 and 2 entered into Diels-Alder additions with dimethyl acetylenedicarboxylate, giving 15 and 16, respectively. Pinofuran (1) also reacted with allyl cations, giving [4+3] cycloadducts 19 and 20. All cycloadditions were π-facially selective, attack occurring exclusively from the face anti to the gem-dimethyl grouping. Further, in the case of cycloadduct 19, extended attack was slightly preferred over compact attack (19ββ : 19αα = 3:2) (α, β, refer to the tetrahydropyranone moiety).     

Synthesis and structural reactivity of inorganic–organic hybrid nanocomposites – A review

Chemistry of hybrid nanocomposites depends mainly on their reactivity and structural relationship. This review mainly reports on the processing techniques of inorganic–organic hybrid nanocomposites and their natural reactivity. Herein, the structure, processing methods and properties of nanocomposites with three different types of matrices are discussed in general. The perusal of this review enables the researchers to design a novel and simple route in processing the hybrid nanocomposites.     

Synthesis and properties of thiophene-functionalized π-extended tetrathiafulvalenes

Two molecular ensembles composed of an array of thiophene-extended tetrathiafulvalene-thiophene were synthesized using Stille coupling and Horner-Wittig reaction as the key steps. Electrochemical redox and electronic absorption properties were investigated by voltammetric and UV-vis spectroscopic analyses.     

Synthesis and reactivity studies of α,α-difluoromethylphosphinates

The preparation and reactivity of some α,α-difluorophosphinates are investigated. Alkylation of H-phosphinates with LiHMDS and ClCF₂H gives the corresponding α,α-difluorophosphinates in good yield. Deprotonation of these reagents with alkyllithium or LDA is then studied. Subtle electronic effects translate into significant differences in the deprotonation/alkylation of the two ‘Ciba-Geigy reagents’ (EtO)₂CRP(O)(OEt)H (R=H, Me). On the other hand, attempted methylation of difluoromethyl-octyl-phosphinic acid butyl ester resulted in the exclusive alkylation of the octyl chain. Finally, reaction with carbonyl compounds results in the formation of 1,1-difluoro-2-phosphinoyl compounds.     

Influence of π-stacking on the N7 and O6 proton affinity of guanine

The influence of π-stacking interactions between guanine (G) and the side chain of tyrosine (Tyr) on the N7 and O6 proton affinities of guanine and on the capability of these sites to act as hydrogen bond acceptors is analyzed at the B3LYP-D, M05-2X and MP2 levels of theory. With all methods, results from full geometry optimizations indicate that stacking interactions increase the N7 and O6 proton affinities by about 5–6 kcal mol^?1, the increase being slightly larger for N7. Consistently with these results, hydrogen bond distances between guanine and one water molecule decrease in the stacked system. Moreover, interaction energy between H₂O and (G-Tyr) is found to be 2–3 kcal mol^?1 larger than in G···H₂O. This strengthening arises from the additional Tyr–H₂O stabilizing interactions and from a cooperative interplay between stacking and hydrogen bond forces.     

Facile and practical synthesis of π-extended oxepins by benzannulation and intramolecular cyclization

π-Extended oxepins 1 and dimer 8 were synthesized by the benzannulation of the corresponding asymmetric diarylacetylene derivatives and 2-(phenylethynyl)benzaldehyde followed by the Cu-catalyzed intramolecular cyclization. The optical properties of the π-extended oxepins 1 and 8 are also investigated.     

Synthesis,structure and reactivity of complexes containing a transition metal–bismuth bond

The transition metal chemistry of bismuth has attracted significant interest since the 1970s. The low cost and high abundance of bismuth(III) reagents, such as the trihalides, makes them ideal starting materials and the size of the bismuth centre allows three- and higher-coordinate complexes to be synthesised, in which the bismuth atom is linked to one or more transition metal fragments. The ability to vary these metal fragments gives access to a plethora of available structures, with cyclopentadienylcarbonyl, metal carbonyl and sandwich compounds of bismuth in existence. Significant recent study has focused on applications in catalysis, where bismuth species can act as cross-coupling agents in carbon–carbon, carbon–nitrogen and carbon–oxygen bond forming reactions. Another striking feature is the variation in bonding situations that can be observed when studying the organometallic chemistry of bismuth. For example, dative and covalent interactions have been reported, in addition to cases of dibismuth acting as a two-, four- or six-electron donating ligand. This review aims to demonstrate the multi-faceted nature of the transition metal chemistry of bismuth and provide a detailed coverage of this topic.     

Dipolar cycloaddition based multi-component reaction: Synthesis of spiro tethered acenaphthylene–indolizine–pyridinone hybrids

The stereoselective syntheses of novel dispiro acenaphthylene–indolizine–pyridinone hybrid heterocycles have been achieved through one-pot four-component domino 1,3-dipolar cycloaddition–Michael addition–air oxidation sequence of reactions.