Biphenol Units Research Articles

Synthesis and Optoelectronic Properties of Threaded BODIPYs.

We report on the synthesis of two new threaded BODIPYs 5 and 6 in good yields using boron as a gathering atom and a macrocycle with a 2,2'-biphenol unit. In addition to usual techniques, they were characterized by X-ray crystallography. Their electrochemical and optical properties were investigated. In particular, both compounds are highly emissive with photoluminescence quantum yields of 54 and 81 % respectively. In addition, they both show a high photostability.

Threading a Linear Molecule Through a Macrocycle Thanks to Boron: Optical Properties of the Threaded Species and Synthesis of a Rotaxane.

Two BODIPYs and two boron β-diketonates were threaded through a macrocycle bearing a 2,2'-biphenol unit, showing thus the ability of boron to act as a gathering atom. The new threaded species were characterized by 1D and 2D NMR spectroscopy as well as by X-ray crystallography for one of them and their properties rationalized with quantum chemistry to unravel the vibronic contributions. The BODIPYs exhibited interesting fluorescence features with quantum yields up to 91 % and enhanced photostability compared to their non-threaded homologues. A rotaxane was synthesized using this threading strategy after stoppering and removing the boron with potassium hydroxide.

Threading a Linear Molecule Through a Macrocycle Thanks to Boron: Optical Properties of the Threaded Species and Synthesis of a Rotaxane

AbstractTwo BODIPYs and two boron β‐diketonates were threaded through a macrocycle bearing a 2,2’‐biphenol unit, showing thus the ability of boron to act as a gathering atom. The new threaded species were characterized by 1D and 2D NMR spectroscopy as well as by X‐ray crystallography for one of them and their properties rationalized with quantum chemistry to unravel the vibronic contributions. The BODIPYs exhibited interesting fluorescence features with quantum yields up to 91 % and enhanced photostability compared to their non‐threaded homologues. A rotaxane was synthesized using this threading strategy after stoppering and removing the boron with potassium hydroxide.

A New Family of Macrocyclic Polyamino Biphenolic Ligands: Acid-Base Study, Zn(II) Coordination and Glyphosate/AMPA Binding

In this study, the ligands 23,24-dihydroxy-3,6,9,12-tetraazatricyclo[17.3.1.1(14,18)]eicosatetra-1(23),14,16,18(24),19,21-hexaene, L1, and 26,27-dihidroxy-3,6,9,12,15-pentaazatricyclo[20.3.1.1(17,21)]eicosaepta-1(26),17,19,21(27),22,24-hexaene, L2, were synthesized: they represent a new class of molecules containing a biphenol unit inserted into a macrocyclic polyamine fragment. The previously synthesized L2 is obtained herein with a more advantageous procedure. The acid-base and Zn(II)-binding properties of L1 and L2 were investigated through potentiometric, UV-Vis, and fluorescence studies, revealing their possible use as chemosensors of H+ and Zn(II). The new peculiar design of L1 and L2 afforded the formation in an aqueous solution of stable Zn(II) mono (LogK 12.14 and 12.98 for L1 and L2, respectively) and dinuclear (LogK 10.16 for L2) complexes, which can be in turn exploited as metallo-receptors for the binding of external guests, such as the popular herbicide glyphosate (N-(phosphonomethyl)glycine, PMG) and its primary metabolite, the aminomethylphosphonic acid (AMPA). Potentiometric studies revealed that PMG forms more stable complexes than AMPA with both L1- and L2-Zn(II) complexes, moreover PMG showed higher affinity for L2 than for L1. Fluorescence studies showed instead that the L1-Zn(II) complex could signal the presence of AMPA through a partial quenching of the fluorescence emission. These studies unveiled therefore the utility of polyamino-phenolic ligands in the design of promising metallo-receptors for elusive environmental targets.

An Alternate [2×2] Grid Constructed Around TiO4 N2 Units.

The formation of a tetranuclear self-assembled species constructed around a TiO4 N2 motif is reported. This aggregate is generated from Ti(Oi Pr)4 , 2,2'-bipyrimidine (bpym) and a bis-biphenol strand (L2 H4 ) where two 2,2'-biphenol units are connected with a biphenyl spacer. The solid-state structure of the [Ti4 (L2 )4 (bpym)4 ] architecture reveals the formation of an unprecedented chiral alternate [2×2] grid. In addition to the structural characterization of the [Ti4 (L2 )4 (bpym)4 ] architecture, geometry optimisation on various possible isomeric tetrameric assemblies ([2×2] grid, alternate [2×2] grid, circular helicate or cyclic hemihelicate) is performed using DFT calculations. These results confirm the higher stability of the alternate [2×2] grid over the other possible tetranuclear isomers and allow examining the replacement of the bpym ligands by two novel diimine chelates within the tetranuclear assembly (2,2'-bipyridine=bipy and 2,2'-bipyrazine=bipyraz). From this initial theoretical investigation, the competition between these three nitrogen ligands in the course of the self-assembly process is next evaluated. Overall, this investigation shows that the exclusive formation of the alternate [2×2] grid is driven by CH⋅⋅⋅N interactions.

Macrocycles of Axially Chiral and Racemic N-Heterocyclic Carbene Silver(I), Gold(I) and Palladium(II) Complexes: Synthesis, Characterization and Computational Structures

In this study, Ag(I), Au(I) and Pd(II) bis -N-hetero-cyclic carbene (NHC) complexes derived from axially chiral R-1,1′-binaphthyl-2,2′-diol (R-BINOL) and racemic biphenyl-2,2′-diol scaffolds have been synthe-sized. The metallation of these bis -imidazolium and bis -triazolium types of ligand precursors of R-BINOL and biphenol unit, viz. (1–4)d has been achieved using standard procedure. The {[L(L′-NHC) 2 ]Ag}Cl-type, chiral (1–2)e and racemic (3–4)e complexes have been obtained by the treatment of ligand with Ag 2 O. Similarly, chiral Pd(II) (1f) and Au(I) (1g) complexes have been synthesized and analysed using spectroscopic techniques. The geometry-optimized structures obtained through the density functional theory display good proximity with the reported X-ray structures of similar type of Ag(I), AAu(I) and Pd(II) complexes.

Supramolecular Interlocked Biphenyl Ligands for Enantioselective Ti-Catalyzed Alkylation of Aromatic Aldehydes

The substitution of tropos 2,2′-biphenols with (S)-amino-acid-derived interaction sites in the 5,5′-position results in a spontaneous desymmetrization. This process is driven by well-defined intermolecular hydrogen bonding, which leads to diastereoselective interlocking of the interaction sites of two biphenol units. The axial chirality of the subunits within the supramolecular dimer is dictated by the chiral information in the interacting selector units. The structure of the complex was investigated by nuclear magnetic resonance spectroscopy, X-ray crystallography, and hydrogen–deuterium exchange. Ligands were successfully employed in the Ti-mediated asymmetric alkylation of aromatic aldehydes.

Isomeric influences of naphthalene based sulfonated poly(arylene ether sulfone) membranes for energy generation using reverse electrodialysis and polymer electrolyte membrane fuel cell

Sulfonated poly(arylene ether sulfone) (SPAES) copolymers possessing three different dihydroxynaphthalene isomers and a biphenol (BP) moiety were synthesized as membranes for energy generation. Membrane samples of three different weight-based ion exchange capacities (IECw, 1.42, 1.82 and 2.2meqg−1) were evaluated through a thermal, mechanical and electrochemical analysis. In order to investigate the isomeric effects of naphthalene and BP units in a polymer matrix, their ion transport properties were studied for potential energy generation applications, exemplified by reverse electrodialysis (RED) and polymer electrolyte membrane fuel cell (PEMFC) applications. Interestingly, the prepared polymeric membranes comprised of three different naphthalene isomers or BP exhibited considerably disparate ion transport properties in both RED and PEMFC applications. In RED applications, 2,6-dihydroxynaphthalene containing SPAES showed high Na+ ion permselectivity and low membrane resistance due to the dense membrane structure and linear conformation of the resulting membrane. In addition, despite having the same IECw, a large difference in the electrochemical performance of the membranes was observed due to isomeric effects in the naphthalene containing polymer backbone. Moreover, in PEMFC single cell tests at 80°C under RH 100% and H2/air feed conditions, the membrane composed of 1,5-dihydroxynaphthalene (IECw=2.2meqg−1), which had a helical conformation, achieved a promising current density (614mAcm−2 at 0.6V) among the tested membranes.

Synthesis and characterization of pendant propane sulfonic acid on phenylene based copolymers by superacid-catalyzed reaction

A series of phenylene based polyelectrolytes were synthesized from 2,2′-biphenol, biphenyl and isatin by superacid catalyzed polyhydroxyalkylation reactions. Grafted sulfonated polymers were synthesized by substitution reaction with 3-bromopropane sulfonic acid potassium salt. These polymers have all carbon–carbon structure on polymer backbone without ether linkage. Particularly, the flexible sulfoalkyl groups were attached to a 2,2′-biphenol unit and formed grafting structure which afforded better stability due to less reactive towards nucleophilic substitution reaction, and good proton mobility because of well phase separation. The structure properties of the synthesized polymers were investigated by 1H NMR spectroscopy. The membranes were studied by ion exchange capacity (IEC), water uptake, dimensional stability, proton conductivity, and cell performance. The chemical deterioration test was performed by Fenton reagent, and compared with normal sulfonated poly(ether sulfone)s and Nafion.

Preparation and characterization of grafted propane sulfonic acid polyphenylene membrane via superacid-catalyzed reaction

A series of polyphenylene-based polyelectrolytes were synthesized from 2,2'-biphenol, and isatin by superacid catalyzed polyhydroxyalkylation reactions. Grafted sulfonated polyphenylenes were synthesized via K2CO3 catalyzed condensation reaction with 3-bromopropane sulfonic acid potassium salt. These polymers have all carbon–carbon linkages without any ether linkage on polymer backbone, which were not attacked by nucleophiles (H2O, hydrogen peroxide, hydroxide anion and radical). Particularly, chemical modification to flexible sulfoalkyl groups implanted to a biphenol unit afforded better stability due to less reactive towards nucleophilic substitution reaction, and good proton mobility because of well phase separation. The structural properties of the synthesized polymers were investigated by 1H NMR spectroscopy. The membranes were studied by ion exchange capacity (IEC), water uptake, dimensional stability as well as proton conductivity assessment. The chemical degradation test was performed by Fenton's reagent, and compared with the usual sulfonated poly(ether sulfone)s and Nafion.

Complexation Enhanced Excited‐State Deactivation by Lithium Ion Coordination to a Borondipyrromethene (Bodipy) Donor–Bridge–Acceptor Dyad

AbstractA donor–acceptor dyad was prepared comprised of a borondipyrromethene (Bodipy) chromophore as the acceptor and a dimethylamino moiety as the donor. The two groups are separated by a 2,2′‐biphenol moiety. The excited state of the Bodipy is efficiently quenched by electron transfer involving donation from the dimethyl amino group. The rate constant for forward electron transfer in DMF was measured to be ca. 2 × 1010 s–1. The charge recombination process is ultrafast. Titration of aliquots of LiClO4 to a DMF solution of the dyad resulted in alterations to the absorption spectrum associated with the 2,2′‐biphenol unit. Changes were modelled as Li+ ions bound to the oxygen atoms of the 2,2′‐biphenol to produce 1:1 (Li+/ligand) and 2:1 (Li+/ligand) complexes. The rate constant for excited state quenching is enhanced upon lithium ion binding.

Synthesis and extension/contraction motion of spiroborate-based double-stranded helicates consisting of substituted oligophenol strands

A new class of ortho- and meta-substituted tetraphenols at the terminal phenyl residues with a biphenylene unit in the middle were synthesized and the effect of the substitution position on the spiroborate-based double-stranded helicate formation with sodium borohydride was investigated. The ortho-substitution considerably hampered the spiroborate formation between the terminal biphenol units and the boron atoms, whereas the meta-substituted oligomers formed a double-stranded helicate bridged by spiroborate groups accommodating a sodium cation in the center, which displayed an extension and contraction motion triggered by the removal and addition of sodium ions in solution.

Synthetic Approaches to Zigzag‐Shaped Oligophenylene Strands Laterally Decorated with Hydroxy Functions

AbstractTwo nanosized zigzag‐shaped oligophenylene strands incorporating 2,2′‐biphenol units were prepared by Suzuki–Miyaura coupling methodology. The two strands are made up of ten and seven phenyl rings, respectively. Two synthetic pathways were evaluated. The first involved the preparation of the target oligophenylene molecules by a sequential approach, whereas the second entailed the formation of the precursors of the target compounds in a one‐step fashion. The efficiencies of these two approaches are discussed and compared.

Synthesis of new compartmental amino-phenolic ligands. Basicity, coordination properties towards Cu(II) and Zn(II) ions. A fluorescent chemosensor for H + and Zn(II)

The syntheses of three new compartmental ligands are reported. Each ligand shows two 1,4,7-triazaheptane (dien) moieties separated by different rigid aromatic groups. The dien unit is linked to the spacer through its central N-atom, while each aromatic moiety contains two hydroxyl-phenolic functions. The synthetic aspects involved in attaching two dien subunits to an aromatic group containing two hydroxyl functions were explored. Each ligand synthesized can coordinate two metal ions positioned far from each other; the single dinuclear units will be useful as building blocks in new supramolecular aggregates. The basicity and binding properties of one of the synthesized ligands (3,3′-bis[ N, N-bis(2-aminoethyl)aminomethyl]-4,4′-dihydroxybiphenyl ( L2)) were potentiometrically studied in aqueous solution. L2 was found to behave as a diprotic acid and as a pentaprotic base under the experimental conditions used. L2 forms stable mononuclear and dinuclear complexes with Cu(II) and Zn(II) ions; the mononuclear species show a tendency to dimerize, while the dinuclear ones are predominant in the presence of two equivalents of M(II) ions in solution. Both protonation and the presence of Zn(II) strongly affect the fluorescence emission properties of L2, which can be used as a new chemosensor for H + and Zn(II) ions. L2 exhibits pH-dependent fluorescence and the emission due to the different protonation of L2 and can be ascribed, above all, to the degree of protonation of the 4,4′-biphenol unit; thus, L2 is more emitting at acidic pH values where the aromatic unit is fully protonated. On the contrary, the Zn-dinuclear species are more emitting from neutral to alkaline pH values exhibiting a CHEF effect which reaches its maximum values (seven times those of the free ligand) at pH 9 with the [Zn 2H −2 L2] 2+ species, thus highlighting the sensing properties of this new chemosensor towards Zn(II).

Recent Advances in Metal-Catalyzed Asymmetric Conjugate Additions

The conjugate addition of carbon nucleophiles to acceptor activated olefins is one of the most important reactions for carbon-carbon bond formation. With optically active metal complexes this transformation can be catalyzed enantioselectively. This review is a collection of the newer literature (since 2001) on this topic. The metal salts and complexes applied are in a broad range, starting from solely Lewis acidic M(II) and M(III) compounds, such as magnesium, zinc, boron, aluminum and the lanthanoids. Transition-metal catalysts suitable for asymmetric conjugate additions are compounds of ruthenium, iridium, nickel, and palladium. The most flourishing fields are, however, the catalysis with rhodium and copper complexes. Rhodium catalysts often have a chiral diphosphane like BINAP, or an optically active olefin as the ligand, the latter being a newer development. The privileged ligand structures for copper catalysts are monodentate phosphoramidites with axially chiral BINOL or other biphenol units.

Rh‐Catalyzed Enantioselective Conjugate Addition of Arylboronic Acids with a Dynamic Library of Chiral tropos Phosphorus Ligands

A library of 19 chiral tropos phosphorus ligands, based on a free-to-rotate (tropos) biphenol unit and a chiral P-bonded alcohol (11 phosphites, 1-P(O)(2)O to 11-P(O)(2)O) or secondary amine (8 phosphoramidites, 12-P(O)(2)N to 19-P(O)(2)N), were screened, individually and in combinations of two, in the rhodium-catalyzed asymmetric conjugate addition of arylboronic acids to enones and enoates. High enantioselectivities (up to 99 % ee) and excellent yields were obtained in the addition to either cyclic or acyclic substrates. The flexible biphenolic P ligands outperformed the analogous rigid binaphtholic P ligands. Variable-temperature (31)P NMR studies revealed that the biphenolic ligands are tropos even at low temperature. Only below 190 K was a coalescence observed; upon further cooling, two atropisomers were detected. The Rh homocomplexes ([Rh(L(a))(2)](+)) were also studied: in general, a single doublet (P-Rh coupling) was observed in the case of the biphenolic phosphite ligands, over the temperature range 380-230 K, demonstrating their tropos nature in the rhodium complexes even at low temperatures. On the other hand, the phosphoramidites showed different behaviors depending on the structure of the ligand and on the nature of the rhodium source. The spectrum at 230 K of the mixture of [Rh(acac)(eth)(2)] (eth=C(2)H(4)) with phosphite 6-P(O)(2)O and phosphoramidite 19-P(O)(2)N (the most enantioselective ligand combination in the conjugate addition reaction) revealed the presence of four homocomplexes (total approximately 40 %: [Rh{6-P(O)(2)O}(2)], [Rh{(aR)-19-P(O)(2)N}(2)], [Rh{(aS)-19-P(O)(2)N}(2)], [Rh{(aR)-19-P(O)(2)N}{(aS)-19-P(O)(2)N}]) and one heterocomplex, [Rh{6-P(O)(2)O}{(aR)-19-P(O)(2)N}] (approximately 60 %) In the heterocomplex, the biphenol-derived phosphite is free to rotate (tropos) while the biphenol-derived phosphoramidite shows a temperature-dependent tropos/atropos behavior (coalescence temperature=310 K).

Rhodium-catalyzed asymmetric reactions with a dynamic library of chiral tropos phosphorus ligands

Abstract Nineteen chiral tropos phosphorus ligands, based on a flexible (tropos) biphenol unit and a chiral P-bound alcohol (11 phosphites) or secondary amine (8 phosphoramidites), were screened, individually and as a combination of two, in various Rh-catalyzed asymmetric reactions. In the Rh-catalyzed asymmetric conjugate addition of phenylboronic acid to cyclic enones, enantiomeric excesses (ee's) up to 95 % were obtained with a 1:1 mixture of a phosphite [derived from (1R,2S)-2-(1-methyl-1-phenylethyl)cyclohexanol] and a phosphoramidite [derived from (S,S)-2,5-diphenylpyrrolidine]. In the mixed Rh precatalyst, which was characterized via 31P-NMR, the biphenol-derived phosphite is free to rotate (tropos) while the biphenol-derived phosphoramidite shows a temperature-dependent tropos/atropos behavior (coalescence temperature = 310 K). The ligands were also screened in the hydrogenation of dehydro-α-amino acids and dehydro-β-amino acids. Ee's up to 98% were obtained for the dehydro-α-amino acids, using the combination of a phosphite [derived from (1R,2S)-2-phenyl-1-cyclohexanol] and a phosphoramidite [derived from (S,S)-bis(α-methylbenzyl)amine]. The reaction was optimized by lowering the phosphite/phosphoramidite ratio to 0.25:1.75 with a resulting improvement of the product ee.

Rh‐Catalyzed Asymmetric Hydrogenation of Prochiral Olefins with a Dynamic Library of Chiral TROPOS Phosphorus Ligands

A library of 19 chiral tropos phosphorus ligands, based on a flexible (tropos) biphenol unit and a chiral P-bound alcohol (11 phosphites) or secondary amine (8 phosphoramidites), was synthesized. These ligands were screened, individually and as a combination of two, in the rhodium-catalyzed asymmetric hydrogenation of dehydro-alpha-amino acids, dehydro-beta-amino acids, enamides and dimethyl itaconate. ee values up to 98% were obtained for the dehydro-alpha-amino acids, by using the best combination of ligands, a phosphite [4-P(O)2O] and a phosphoramidite [13-P(O)2N]. Kinetic studies of the reactions with the single ligands and with the combination of phosphite [4-P(O)2O] and phosphoramidite [13-P(O)2N] have shown that the phosphite, despite being less enantioselective, promotes the hydrogenation of methyl 2-acetamidoacrylate and methyl 2-acetamidocinnamate faster than the mixture of the same phosphite with the phosphoramidite, while the phosphoramidite alone is much less active. In this way, the reaction was optimized by lowering the phosphite/phosphoramidite ratio (the best ratio is 0.25 equiv phosphite/1.75 equiv phosphoramidite) with a resulting improvement of the product enantiomeric excess. A simple mathematical model for a better understanding of the variation of the enantiomeric excess with the phosphite/phosphoramidite ratio is also presented.

Rh-catalysed asymmetric hydrogenations with a dynamic library of chiral tropos phosphorus-ligands

A library of 16 chiral tropos phosphorus-ligands, based on a chiral P-bound alcohol or secondary amine and a flexible (tropos) P-bound biphenol unit, was synthesised. This ligand library allowed the screening of 16 homocombinations and 115 heterocombinations for the rhodium catalysed asymmetric hydrogenation of methyl N-acetamido acrylate. The screening resulted in the identification of a phosphite/phosphoramidite heterocombination, which proved to be extremely effective and enantioselective (100% yield, 94% ee).

Thin-film polymerization and characterization of Sumitomo's Sumikasuper®-type liquid crystalline polymers

Using the thin film polymerization approach, we have studied the texture evolution when synthesizing a novel liquid crystalline polymer (LCP) system based on Sumikasuper® LCPs. The main monomers used were p-acetoxybenzoic acid (ABA), 4,4′-biphenol (BP), isophthalic acid (IA), phthalic acid (PA) and terephthalic acid (TA). Polarizing optical microscopy (POM), FTIR, X-ray diffraction (XRD) and atomic force microscopy (AFM) were employed to study the thin film polymerization process and characterize the products. The generation and evolution of liquid crystal phases were monitored; the results revealed that there exists a composition range for the monomers to react and form liquid crystal materials. The critical temperature for LC formation in ABA/BP/IA system decreased with increasing ABA content. FTIR results confirmed the formation of polymers. AFM investigation suggested a similar process of morphological change to that observed using POM. An increasing surface roughness of the thin films with the progress of polymerization was also obtained from AFM analysis. A nematic LC texture of the polymer system was suggested by XRD examination. Results obtained by replacing BP with acetylated BP, and by conducting polymerization using two-monomer systems, suggest that BP units are included in polymers obtained by the thin film polymerization method.