Amine-modified polyionic liquid supports enhance the efficacy of PdNPs for the catalytic hydrogenation of CO2 to formate.

Palladium nanoparticles stabilised by aniline modified polymer immobilised ionic liquid is a remarkably active catalyst for the hydrogenation of CO2 to formate; the initial TOF of 500 h-1 is markedly higher than either unmodified catalyst or its benzylamine and N,N-dimethylaniline modified counterparts and is among the highest to be reported for a PdNP-based catalyst.

Hybridising inorganic materials with fluorescent BOPHY dyes: A structural and optical comparative study.

This study presents the design and characterization of new monochromatic light-harvesting systems based on inorganic porous materials hybridized with organic dye molecules within their structure. A new fluorescent BOPHY dye was prepared, characterized optically and used as both reference and synthetic precursor for two alkoxysilane derivatives that were incorporated separately within a silica structure. The dyes, one bearing one alkoxysilane group and the other one two, were co-condensed with tetraethyl orthosilicate to form a hybrid organo-silica framework, where they are found at specific locations. The structure of the new materials was analysed by powder XRD and TEM, which confirmed the presence of the hexagonal pore arrangement typical of mesoporous MCM-41 silica particles. The steady-state and time-resolved analysis showed that the particles where the dyes are most dispersed within the framework retain the highest fluorescence quantum yield, up to 0.63, in the green-yellow region of the visible spectrum. On the other hand, increasing the content of BOPHY units in the solid matrix seem to favour non-radiative deactivation pathways and aggregation phenomena, which lower the efficiency of light emission. The materials also exhibit interesting properties, such as a dual excited-state decay and fluorescence anisotropy. The short fluorescence lifetime, about 2 ns, matches the typical singlet lifetime of BOPHY dyes, whereas the long component, up to 20 ns, is attributed to delayed fluorescence, which could take place via charge recombination. Optical anisotropy experiments revealed that all materials show polarised light emission to a significant extent and, for most samples, it was also possible to determine a polarisation transfer decay trace, from 400 to 800 ps This is ascribed to the occurrence of energy migration between neighbouring dye units within the silica structure.

Synthesis and Reactivity of 3,5-Diiodo-BODIPYs via a Concerted, Double Aromatic Finkelstein Reaction.

3,5-Diiodo-8-aryl-BODIPYs are prepared from the corresponding 3,5-dichloro- and 3,5-dibromo- congeners via a double aromatic Finkelstein reaction with NaI in refluxing propionitrile, in yields from 51 to 100%. Rate enhancement is observed for 3,5-dibromo-BODIPYs (ArBr > ArCl) suggesting a concerted SNAr mechanism for this transformation. Thus formed 3,5-diiodo-BODIPYs are examined as coupling partners in Migita-Kosugi-Stille, Mizoroki-Heck, Sonogashira, and Suzuki-Miyaura reactions, providing routes toward complex BODIPY architectures.

Synthesis, Structure and Photophysical Properties of a New Class of Inherently Chiral Boron(III) Chelates-The tert-Leucine Complexes.

A new family of boron(III) chelates is introduced whereby molecular chirality, confirmed by circular dichroism, is imported during synthesis such that isolation of the diastereoisomers does not require separation procedures. The photophysical properties of two members of the family have been examined: the N,O,O-salicylaldehyde-based derivative shows pronounced intramolecular charge-transfer character in fluid solution and is weakly fluorescent, with a large Stokes shift. The corresponding 2-methylamino-benzaldehyde-derived N,N,O-chelate absorbs and fluoresces in the visible region with a much smaller Stokes shift. Orange fluorescence is also observed for this compound as a cast film. Temperature-dependence studies show that decay of the fluorescent state is weakly activated but emission is less than quantitative at 77 K. Quite rare for boron(III)-based chelates, this derivative undergoes intersystem crossing to form a meta-stable triplet-excited state. X-ray crystal structures are reported for both compounds, along with simulated ECD spectra.

A new chiral boron-dipyrromethene (BODIPY)-based fluorescent probe: molecular docking, DFT, antibacterial and antioxidant approaches.

A new chiral BODIPY-based fluorescent compound, 5-bromo-4,4-difluoro-3(S)-1-phenylethyl)amino) BODIPY, 4 was synthesized for biomedical applications. Optical, antimicrobial, antioxidant properties of the compound 4 are investigated. The partition coefficient suggested that the compound 4 has the potential to be developed as an active antibacterial and antioxidant candidate. In this context, antibacterial assay was carried out for compound 4 against various bacterial strains, revealing maximum inhibition zone (24 ± 2.19 mm) in Escherichia coli. Moreover, results of antioxidant activity of compound 4 revealed IC50 values to be greater than ascorbic acid. Molecular docking has given brief insight about the binding of the compound 4, suggesting that it has a strong potential to inhibit bacterial target enzymes viz., DNA gyrase, enzymes in the type II fatty acid synthesis and Ddl (d-alanine: d-alanine ligase) in peptidoglycan synthesis. The molecular geometry and electrostatic potential of compound 4, was established by DFT (Density Functional Theory) calculations.AbbreviationsBBBblood‒brain barrierBDEbond dissociation energyBODIPYboron-dipyrromethaneDdlD-alanine:D-alanine ligaseDDQ2,3-dichloro-5,6-dicyano-1,4-benzoquinoneDFTdensity functional theoryDNAdeoxyribonucleic acidDPPH1,1‒diphenyl‒2‒picrylhydrazylNBSN-bromo succinimideROSreactive oxygen speciesUV-visultraviolet-visibleFMOfrontier molecular orbitalsHOMOhighest occupied molecular orbitalLUMOlowest unoccupied molecular orbitalCommunicated by Ramaswamy H. Sarma.

Optical spectroscopic properties recorded for simple BOPHY dyes in condensed media: The mirror-symmetry factor.

The BOPHY structural scaffold provides opportunities for the synthesis of innumerable derivatives with linear geometries and well-controlled π-conjugation pathways. The simpler BOPHY chromophores are highly fluorescent but exhibit poor mirror symmetry between absorption and fluorescence spectra at ambient temperature. In particular, the absorption (and excitation) spectra are broad and appear as two overlapping bands of comparable intensity. In constrained media, such as low-temperature rigid glasses or stretched poly(ethylene) films, mirror symmetry is restored. Analysis of the temperature dependence recorded for simple BOPHY derivatives indicates that the vibronic envelope accompanying the electronic transitions can be well described in terms of low- and medium-frequency modes. Whereas the fluorescence spectral profile is only weakly dependent on temperature, the excitation spectrum is far more affected. The magnitude of the low-frequency mode, and the associated electron-phonon coupling, increase substantially with increasing temperature and is responsible for temperature broadening and distortion of the excitation spectrum in solution. This critical low-frequency vibronic mode is associated with out-of-plane torsional bending of the BOPHY unit. Variable temperature NMR studies failed to provide unequivocal evidence for conformational changes of one of the derivatives over the temperature range 193-353 K.

Synthesis of 2-aminoBODIPYs by palladium catalysed amination.

Palladium catalysed coupling of the 2-iodoBODIPY 3 with a range of anilines and a primary alkylamine succeeds in generating the corresponding 2-aminoBODIPYs. These 2-aminoBODIPY derivatives are non-emissive and quantum chemical calculations and electrochemistry are consistent with charge transfer from the amine substituent. Attenuation of this charge transfer pathway by conversion of the 1,2-phenylenediamine derivative 9 into the corresponding benzimidazolone 10 restores the fluorescence and has been used as the basis for a fluorescence sensor for phosgene.

Thermally-Activated, Delayed Fluorescence in O,B,O- and N,B,O-Strapped Boron Dipyrromethene Derivatives.

A small series of boron dipyrromethene (BODIPY) dyes has been synthesized whereby the boron atom is constrained in a five-membered ring formed from either o-dihydroxypyridine or o-aminophenol. In the latter case, the amino group has been converted into the corresponding amide derivative so as to curtail the possibility for light-induced charge transfer from strap to BODIPY. These compounds are weakly emissive in fluid solution but cleavage of the strap, by treatment with a photoacid generator, restores strong fluorescence. Surprisingly, the same compounds remain weakly fluorescent in a rigid glass at 80 K where light-induced charge transfer is most unlikely. In fluid solution, the fluorescence quantum yield increases with increasing temperature due to a thermally activated step but does not correlate with the thermodynamics for intramolecular charge transfer. It is proposed that the strap causes rupture of the potential energy surface for the excited state, creating traps that provide new routes by which the wave packet can return to the ground state. Access to the trap from the excited state is reversible, leading to the delayed emission. Analysis of the temperature dependent emission intensities allows estimation of the kinetic parameters associated with entering and leaving the trap.

Circularly Polarized Luminescence from Helically Chiral N,N,O,O-Boron-Chelated Dipyrromethenes.

Helically chiral N,N,O,O-boron chelated dipyrromethenes showed solution-phase circularly polarized luminescence (CPL) in the red region of the visible spectrum (λem (max) from 621 to 663 nm). The parent dipyrromethene is desymmetrised through O chelation of boron by the 3,5-ortho-phenolic substituents, inducing a helical chirality in the fluorophore. The combination of high luminescence dissymmetry factors (|glum | up to 4.7 ×10(-3) ) and fluorescence quantum yields (ΦF up to 0.73) gave exceptionally efficient circularly polarized red emission from these simple small organic fluorophores, enabling future application in CPL-based bioimaging.

Synthesis of 3-aminoBODIPY dyes via copper-catalyzed vicarious nucleophilic substitution of 2-halogeno derivatives.

2-Halogeno BODIPYs undergo copper catalysed nucleophilic substitution with alkyl amines and anilines and an amide to give the corresponding 3-aminoBODIPY derivatives. The substrates are readily prepared by the regioselective 2-halogenation of the chemically robust, preformed BODIPYs thus providing an alternative to direct nucleophilic substitution of the corresponding 3-halogenoBODIPYs which requires regioselective 3-halogenation of the more sensitive dipyrromethane intermediate. 2-Halogenation expands the scope of vicarious substitution of BODIPYs to include weaker nitrogen nucleophiles.

Synthesis of an electron-rich KITPHOS monophosphine, preparation of derived metal complexes and applications in catalysis.

This protocol describes the synthesis of a representative example of the electron-rich biaryl-like KITPHOS class of monophosphine, 11-dicyclohexylphosphino-12-phenyl-9,10-dihydro-9,10-ethenoanthracene (H-KITPHOS). The bicyclic architecture of H-KITPHOS is constructed via [4+2] Diels-Alder cycloaddition between 1-(dicyclohexylphosphinoylethynyl)benzene and anthracene. H-KITPHOS monophosphine is prepared via an operationally straightforward three-step procedure and is isolated in an overall yield of ∼55%. The synthesis of palladium and gold precatalysts of H-KITPHOS are also described; the yields of analytically pure complexes are high (75-85% and 85-90%, respectively). The palladium complex of H-KITPHOS forms a highly active catalyst for C-C and C-N cross-coupling of a range of aryl and heteroaryl chlorides and bromides, and the electrophilic Lewis acid gold complex efficiently catalyzes a host of cycloisomerizations. The total time required for the synthesis of H-KITPHOS is 95 h; the preparation of corresponding palladium and gold precatalysts requires an additional 7-8 h, and, if necessary, crystallizations will require a further 48 h.

Rhodium-catalyzed double [2 + 2 + 2] cycloaddition of 1,4-bis(diphenylphosphinoyl)buta-1,3-diyne with tethered diynes: a modular, highly versatile single-pot synthesis of NU-BIPHEP biaryl diphosphines.

Rhodium-catalyzed double [2 + 2 + 2] cycloaddition of 1,4-bis(diphenylphosphinoyl)buta-1,3-diyne with tethered diynes provides a straightforward, single-pot procedure for the synthesis of a new class of tropos biaryl diphosphine, NU-BIPHEP. This methodology represents a significant improvement on existing multistep procedures. Enantiopure Lewis acid platinum complexes of these diphosphines are highly efficient catalysts for carbonyl-ene and Diels-Alder reactions, and ruthenium diphosphine-diamine complexes catalyze the asymmetric reduction of ketones to give ee's that rival those obtained with their BINAP counterpart.

Asymmetric platinum group metal-catalyzed carbonyl-ene reactions: carbon-carbon bond formation versus isomerization.

A comparative study of the carbonyl-ene reaction between a range of 1,1'-disubstituted or trisubstituted alkenes and ethyl trifluoropyruvate catalyzed by Lewis acid-platinum group metal complexes of the type [M{(R)-BINAP}]2+ (M = Pt, Pd, Ni; BINAP is 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl) revealed subtle but significant differences in their reactivity. For instance, the palladium-based Lewis acid [Pd{(R)-BINAP}]2+ catalyzes the ene reaction between methylene cycloalkane to afford the expected alpha-hydroxy ester in good yield and excellent diastereo- and enantioselectivity. In contrast, under the same conditions, the corresponding [M{(R)-BINAP}]2+ (M = Pt, Ni) catalyzes isomerization of methylene cycloalkane and the ene reaction of the resulting mixture of methylene cycloalkane and 1-methylcycloalkene at similar rates to afford a range of -hydroxy esters in high regioselectivity, good diastereoselectivity, and good to excellent enantioselectivity. In addition, [Pt{(R)-BINAP}]2+ also catalyzes postreaction isomerization of the ene product as well as consecutive ene reactions to afford a double carbonyl-ene product. The sense of asymmetric induction has been established by single-crystal X-ray crystallography, and a stereochemical model consistent with the formation of (S)-configured -hydroxy ester has been proposed; the same model also accounts for the observed exo-diastereoselectivity as well as the level of diastereoselectivity.

The first insoluble polymer-bound palladium complexes of 2-pyridyldiphenylphosphine: highly efficient catalysts for the alkoxycarbonylation of terminal alkynes.

Palladium complexes of 2-pyridyldiphenylphosphine anchored on polystyrene, polymethylmethacrylate and styrene-methylmethacrylate copolymer form highly active heterogeneous catalysts for the alkoxycarbonylation of terminal alkynes with activities approaching those obtained under homogeneous conditions.

Highly efficient asymmetric Lewis acid catalysis with platinum group complexes of conformationally flexible 1,3-butadiene-bridged diphosphines, NUPHOS.

[structure: see text] Palladium and platinum complexes of conformationally flexible 1,3-butadiene-bridged diphosphines NUPHOS can be resolved with (S)-BINOL at elevated temperatures to afford diastereopure delta-[(NUPHOS)M[(S)-BINOL]] (M = Pd, Pt). The homochiral Lewis acid complexes delta-[(NUPHOS)M][OTf](2), generated by protonation of delta-[(NUPHOS)M[(S)-BINOL]] with trifluoromethanesulfonic acid, catalyze the Diels-Alder reaction between acryloyl-N-oxazolidinones and cyclopentadiene to give ee values up to 96%. The corresponding enantiopure dichlorides delta-[(NUPHOS)PtCl(2)] react with AgClO(4) to form highly efficient catalysts that give good endo/exo selectivities and high endo enantioselectivity.