Excess Of Trifluoroacetic Acid Research Articles

Synthesis and characterization of azulene-based BO-doped heteroaromatics

Simultaneously incorporating heteroatoms and nonbenzenoid aromatic hydrocarbons, such as azulene, into polycyclic aromatic hydrocarbons, offers a robust strategy for designing molecules with aesthetic appeal and unique properties. This study presents the successful synthesis and characterization of a series of azulene-based BO-doped heteroaromatics. Investigation into their optical and electrochemical properties, through UV–vis absorption, cyclic voltammetry, and DFT calculations, reveal their sensitivity to fluoride ions, making them promising candidates for chemosensor applications. Notably, unlike the parent azulene, which is sensitive to acid, these new compounds show negligible changes in absorption and NMR spectra when exposed to excess trifluoroacetic acid. This observation suggests that the introduction of BO unit effectively restrains the protonation of azulene moiety.

Luminescence of 1,3,6-trisubstituted pyrazolo[3,4-d][1,2,3]triazoles

The photophysical properties of four 1,3,6-trisubstituted pyrazolo[3,4- d][1,2,3]triazoles were studied by a combination of UV–vis and fluorescence spectroscopy as well as density functional theory (DFT) and time-dependent DFT calculations. All four compounds are weakly fluorescent. Upon protonation with trifluoroacetic acid, all compounds display a drastic luminescence turn-on. The addition of excess trifluoroacetic acid further enhances the luminescence intensity, which is tentatively attributed to the formation of extended hydrogen bonding network rather than the formation of doubly protonated 1,3,6-trisubstituted pyrazolo[3,4- d][1,2,3]triazoles. All new compounds were characterized by nuclear magnetic resonance and X-ray crystallography.

Mononuclear nickel(II) dithiolate complexes with chelating diphosphines: Insight into protonation and electrochemical proton reduction

Inspired by the metal active sites of [FeFe]- and [NiFe]‑hydrogenases, a series of mononuclear Ni(II) ethanedithiolate complexes [{(Ph2PCH2)2×}Ni(SCH2CH2S)] (X = NCH2C5H4N-p (2a), NCH2C6H5 (2b), NCH2CHMe2 (2c), and CH2 (2d)) with chelating diphosphines were readily synthesized through the room-temperature treatments of mononuclear Ni(II) dichlorides [{(Ph2PCH2)2×}NiCl2] (1a-1d) with ethanedithiol (HSCH2CH2SH) in the presence of triethylamine (Et3N) as acid-binding agent. All the as-prepared complexes 1a-1d and 2a-2d are fully characterized through elemental analysis, nuclear magnetic resonance (NMR) spectrum, and by X-ray crystallography for 1b, 2a-2d. To further explore proton-trapping behaviors of this type of mononuclear Ni(II) complexes for catalytic hydrogen (H2) evolution, the protonation and electrochemical proton reduction of 2a-2c with aminodiphosphines (labeled PCNCP = (Ph2PCH2)2NR) and reference analogue 2d with nitrogen-free diphosphine (dppp = (Ph2PCH2)2CH2) are studied and compared under trifluoroacetic acid (TFA) as a proton source. Interestingly, the treatments of 2a-2d with excess TFA resulted in the unexpected formation of dinuclear Ni(II)-Ni(II) dication complexes [{(Ph2PCH2)2×}2Ni2(μ-SCH2CH2S)](CF3CO2)2 (3a-3d) and mononuclear Ni(II) N-protonated complexes [{(Ph2PCH2)2N(H)R}Ni(SCH2CH2S)](CF3CO2) (4a-4c), which has been well supported by high-resolution electrospray ionization mass spectroscopy (HRESI-MS), NMR (31P, 1H) as well as fourier transform infrared spectroscopy (FT-IR) techniques, and especially by X-ray crystallography for 3d. Additionally, the electrochemical properties of 2a-2d are investigated in the absence and presence of strong acid (TFA) by using cyclic voltammetry (CV), showing that the complete protonation of 2a-2d gave rise to dinuclear Ni2S2 species 3a-3d for electrocatalytic proton reduction to H2.

Twisted One-Dimensional Charge Transfer and Related Y-Shaped Chromophores with a 4H-Pyranylidene Donor: Synthesis and Optical Properties.

Three series of push–pull derivatives bearing 4H-pyranylidene as electron donor group and a variety of acceptors were designed. On one hand, one-dimensional chromophores with a thiophene ring (series 1H) or 5-dimethylaminothiophene moiety (series 1N) as an auxiliary donor, non-coplanar with the π-conjugated system, were synthesized. On the other hand, related two-dimensional (2D) Y-shaped chromophores (series 2) were also prepared to compare how the diverse architectures affect the electrochemical, linear, and second-order nonlinear optical (NLO) properties. The presence of the 5-dimethylaminothiophene moiety in the exocyclic C=C bond of the pyranylidene unit gives rise to oxidation potentials rarely low, and the protonation (with an excess of trifluoroacetic acid) of its derivatives results in the apparition of a new blue-shifted band in the UV–visible spectra. The analysis of the properties of derivatives with and without the additional thiophene ring shows that this auxiliary donor leads to a higher NLO response, accompanied by an enhanced transparency. Y-shaped chromophores of series 2 present a blue-shifted absorption, higher molar extinction coefficients, and higher Eox values compared to their linear twisted counterparts. As concerns NLO properties, 2D Y-shaped architecture gives rise to somewhat lower μβ values (except for thiobarbiturate derivatives).

Tuning the Photophysical Properties of Spirolactam Rhodamine Photoswitches

AbstractSpirolactam rhodamines are fluorescent photoswitches that are useful for single molecule localization microscopy, volumetric 3D digital light photoactivatable dye displays, and other applications. Measurement of the photophysical properties, particularly photoswitching kinetics and quantum yields, is challenging and a comprehensive understanding of how molecular structure affects these parameters remains incomplete. In this study, we have synthesized a series of N‐aryl spirolactam rhodamine photoswitches with fluorescent emissions at 585 nm and 518 nm. Extinction coefficients and fluorescence quantum yields of the fluorescent form of the photoswitch have been measured using excess trifluoroacetic acid to drive the equilibrium to the open form. A method to determine photoswitching kinetics and quantum yields was developed by monitoring the kinetics to reach equilibrium between the on‐state and off‐state and fitting this data to a rate equation for a reaction in equilibrium. Trends based on the electronic and steric properties of the aryl substituents were evaluated. Using this information, a proof‐of‐principle demonstration of 3D voxel formation was accomplished using a green (518 nm) emitting photoswitch, setting the foundation for a multi‐colour volumetric 3D display.

Amine‐containing tertiary phosphine‐substituted diiron ethanedithioate (edt) complexes Fe2(μ‐edt)(CO)6‐nLn (n= 1, 2): Synthesis, protonation, and electrochemical properties

As diiron subsite models of [FeFe]‐hydrogenases for catalytic proton reduction to hydrogen (H2), a new series of the phosphine‐substituted diiron ethanedithiolate complexes Fe2(μ‐edt)(CO)6‐nLn (n = 1, 2) were prepared from the variable substitutions of all‐CO precursor Fe2(μ‐edt)(CO)6 (A) and tertiary phosphines (L1‐L4) under different reaction conditions. While the Me3NO‐assisted substitutions of A and one equiv. ligands L1‐L4 [L = Ph2P(CH2NHBut), Ph2P(CH2CH2NH2), Ph2P(NHBut), and Ph2P(C6H4Me‐p)] produced the monosubstituted complexes Fe2(μ‐edt)(CO)5L (1–4) in good yields, the refluxing xylene solution of A and two equiv. ligand L1 prepared complex Fe2(μ‐edt)(CO)5{κ1‐Ph2P(CH2NHBut)} (1) in low yield. Meanwhile, the UV‐irradiated toluene solution of A and two equiv. ligand L3 resulted in the rare formation of the disubstituted complex Fe2(μ‐edt)(CO)4{κ1, κ1‐(Ph2PNHBut)2} (5) in low yield, whereas the Me3NO‐assisted substitution of A and two equiv. ligand L4 afforded the disubstituted complex Fe2(μ‐edt)(CO)4{κ1, κ1‐(Ph2PC6H4Me‐p)2} (6) in good yield. All the model complexes 1–6 have been characterized by elemental analysis, FT‐IR, NMR spectroscopy, and particularly for 1, 3, 5 by X‐ray crystallography. Further, the protonations of complexes 1–4 are studied and compared with excess acetic acid (HOAc) and trifluoroacetic acid (TFA) by using FT‐IR and NMR techniques. Additionally, the electrochemical and electrocatalytic properties of model complexes 1–6 are investigated and compared by cyclic voltammetry (CV), suggesting that they are electrocatalytically active for proton reduction to H2 in the presence of HOAc.

Fourier-transform infrared spectroscopy for monitoring proteolytic reactions using dry-films treated with trifluoroacetic acid

In this study we explore the potential of using Fourier-transform infrared (FTIR) spectra of trifluoroacetate-protein and peptide complexes for monitoring proteolytic reactions. The idea of treating dry-films of protein hydrolysates with trifluoroacetic acid (TFA) prior to FTIR analysis is based on the unique properties of TFA. By adding a large excess of TFA to protein hydrolysate samples, the possible protonation sites of the proteins and peptides will be saturated. In addition, TFA has a low boiling point when protonated as well as complex-forming abilities. When forming TFA-treated dry-films of protein hydrolysates, the excess TFA will evaporate and the deprotonated acid (CF3COO−) will interact as a counter ion with the positive charges on the sample materials. In the study, spectral changes in TFA-treated dry-films of protein hydrolysates from a pure protein and poultry by-products, were compared to the FTIR fingerprints of untreated dry-films. The results show that time-dependent information related to proteolytic reactions and, consequently, on the characteristics of the protein hydrolysates can be obtained. With additional developments, FTIR on dry-films treated with TFA may be regarded as a potential future tool for the analysis of all types of proteolytic reactions in the laboratory as well as in industry.

Synthesis of Expanded Porphyrinoids with Azulene and Indene Subunits and an opp-Dioxadicarbaporphyrin from Fulvene Carbinols and a Dioxacarbatripyrrin.

In an attempt to prepare quatyrin derivatives, which are hydrocarbon analogues of the porphyrins, azulene-appended fulvene carbinols were self-condensed in the presence of BF3·Et2O. Although these investigations failed to give structures related to quatyrin, expanded porphyrin analogues were obtained instead. In dichloromethane, the major macrocyclic product consisted of three fulvene units, but when chloroform was used as the reaction solvent, a tetrafulvene macrocycle was isolated. Self-condensation of a furan-appended fulvene alcohol gave trace amounts of an opp-dioxadicarbaporphyrin. An alternative route to this novel system was developed where a dioxacarbatripyrrin was condensed with an indene dialdehyde in the presence of HBr. The heterodicarbaporphyrinoid proved to have strong globally aromatic properties as assessed by 1H NMR spectroscopy, anisotropy of induced current density, and NICS calculations. In the presence of excess trifluoroacetic acid, an unstable aromatic cation was formed by C-protonation of an indene subunit. This species was also highly diatropic, and the 1H NMR spectrum gave an unusually high Δδ value of 17.46 ppm.

Stability of a Series of BODIPYs in Acidic Conditions: An Experimental and Computational Study into the Role of the Substituents at Boron.

Boron-dipyrromethene (BODIPY) dyes have been extensively investigated in recent years for a variety of bioanalytical and bioimaging applications. The success of these applications relies on the stability of BODIPYs, particularly under acidic conditions. In this work, the stability of a series of 4,4′-disubstituted BODIPYs (−F, −CN, −Ph, −Me, −OMe) toward addition of excess trifluoroacetic acid (TFA) was studied systematically and comprehensively through 11B and 1H NMR, UV–vis, fluorescence, thin layer chromatography, mass spectrometry, and infrared. The results indicate that 4,4′-dicyano-BODIPY 2 is the most stable among this series and remains unchanged even 3 days after addition of excess TFA. On the other hand, 4,4′-dimethyl-BODIPY 3 and 4,4′-dimethoxy-BODIPY 5 are the least stable, toward addition of TFA, and the 4,4′-diphenyl and 4,4′-difluoro-BODIPYs 1 and 4 were found to have intermediate stability. The experimental analysis and comparison with theoretical calculations indicate that the 4,4′-dicyano-BODIPY 2 has the greater aromaticity of the series, as evaluated by the BLA parameter, decreased charge on boron, and upon TFA addition it forms an unusually stable BODIPY 2···TFA complex. On the other hand, all other BODIPYs decompose within hours after TFA addition. Computational modeling demonstrates that 4,4′-dicyano substitution increases aromaticity and stabilizes the B–N bond, resulting in the most stable compound from the series studied.

Catalytic Hydroxylation of Benzene to Phenol by Dioxygen with an NADH Analogue.

Hydroxylation of benzene by molecular oxygen (O2 ) occurs efficiently with 10-methyl-9,10-dihydroacridine (AcrH2 ) as an NADH analogue in the presence of a catalytic amount of Fe(ClO4 )3 or Fe(ClO4 )2 with excess trifluoroacetic acid in a solvent mixture of benzene and acetonitrile (1:1 v/v) to produce phenol, 10-methylacridinium ion and hydrogen peroxide (H2 O2 ) at 298 K. The catalytic oxidation of benzene by O2 with AcrH2 in the presence of a catalytic amount of Fe(ClO4 )3 is started by the formation of H2 O2 from AcrH2 , O2 , and H(+) . Hydroperoxyl radical (HO2 (.) ) is produced from H2 O2 with the redox pair of Fe(3+) /Fe(2+) by a Fenton type reaction. The rate-determining step in the initiation is the proton-coupled electron transfer from Fe(2+) to H2 O2 to produce HO(.) and H2 O. HO(.) abstracts hydrogen rapidly from H2 O2 to produce HO2 (.) and H2 O. The Fe(3+) produced was reduced back to Fe(2+) by H2 O2 . HO2 (.) reacts with benzene to produce the radical adduct, which abstracts hydrogen from AcrH2 to give the corresponding hydroperoxide, accompanied by generation of acridinyl radical (AcrH(.) ) to constitute the radical chain reaction. Hydroperoxyl radical (HO2 (.) ), which was detected by using the spin trap method with EPR analysis, acts as a chain carrier for the two radical chain pathways: one is the benzene hydroxylation with O2 and the second is oxidation of an NADH analogue with O2 to produce H2 O2 .

Synthesis, Structure and Redox Properties of Asymmetric (Cyclopentadienyl)(ene‐1,2‐dithiolate)cobalt(III) Complexes Containing Phenyl, Pyridyl and Pyrazinyl Units

AbstractThe compounds [(η5‐C5H5)Co{SC(H)CRS}] [R = phenyl (1), pyridin‐3‐yl (2) or pyrazin‐2‐yl (3)] have been synthesized and characterized by elemental analysis, 1H NMR, mass spectrometry and X‐ray crystallography. The variation in the UV/Vis and redox properties of these compounds alone and upon acidification has been investigated. In CH2Cl2 solution each compound undergoes a reversible one‐electron reduction, and the EPR spectrum of each monoanion has been recorded. In the presence of a 5:1 excess of trifluoroacetic acid the one‐electron reduction of both 2 and 3 occurs at a less negative potential. The information obtained has been interpreted with the aid of DFT calculations for [1]y, [2]y and [3]y (y = 0 or –1) and the monoprotonated forms [2H]z and [3H]z (z = +1 or 0), and this has provided insight into the nature of the redox‐active orbitals in these complexes. The HOMOs and LUMOs of these species are delocalized and each involves contributions from cobalt, ene‐1,2‐dithiolate and R orbitals. The information from the experimental and theoretical investigations is used to suggest that, for the pyran ring‐opened form of the molybdenum cofactor of oxygen‐atom‐transfer enzymes, the pterin may participate in the redox reactions involved in the catalytic cycle.

High-valent chromium-oxo complex acting as an efficient catalyst precursor for selective two-electron reduction of dioxygen by a ferrocene derivative.

Efficient catalytic two-electron reduction of dioxygen (O2) by octamethylferrocene (Me8Fc) produced hydrogen peroxide (H2O2) using a high-valent chromium(V)-oxo corrole complex, [(tpfc)Cr(V)(O)] (tpfc = tris(pentafluorophenyl)corrole) as a catalyst precursor in the presence of trifluoroacetic acid (TFA) in acetonitrile (MeCN). The facile two-electron reduction of [(tpfc)Cr(V)(O)] by 2 equiv of Me8Fc in the presence of excess TFA produced the corresponding chromium(III) corrole [(tpfc)Cr(III)(OH2)] via fast electron transfer from Me8Fc to [(tpfc)Cr(V)(O)] followed by double protonation of [(tpfc)Cr(IV)(O)](-) and facile second-electron transfer from Me8Fc. The rate-determining step in the catalytic two-electron reduction of O2 by Me8Fc in the presence of excess TFA is inner-sphere electron transfer from [(tpfc)Cr(III)(OH2)] to O2 to produce the chromium(IV) superoxo species [(tpfc)Cr(IV)(O2(•-))], followed by fast proton-coupled electron transfer reduction of [(tpfc)Cr(IV)(O2(•-))] by Me8Fc to yield H2O2, accompanied by regeneration of [(tpfc)Cr(III)(OH2)]. Thus, although the catalytic two-electron reduction of O2 by Me8Fc was started by [(tpfc)Cr(V)(O)], no regeneration of [(tpfc)Cr(V)(O)] was observed in the presence of excess TFA, regardless of the tetragonal chromium complex being to the left of the oxo wall. In the presence of a stoichiometric amount of TFA, however, disproportionation of [(tfpc)Cr(IV)(O)](-) occurred via the protonated species [(tpfc)Cr(IV)(OH)] to produce [(tpfc)Cr(III)(OH2)] and [(tpfc)Cr(V)(O)].

A Novel Acylmethylpyridinol Ligand Containing Dinuclear Iron Complex Closely Related to [Fe]-Hydrogenase

On synthesizing the PMB-protected mononuclear iron complexes [2-C(O)CH2-6-PMBOC5H3N]Fe(CO)3I (6) and [2-C(O)CH2-6-PMBOC5H3N]Fe(CO)2(2-SC5H4N) (7), the novel acylmethylpyridinol ligand containing dinuclear iron complex [2-C(O)CH2-6-HOC5H3N]Fe2(CO)4[2′-C(O)CH2-6′-OC5H3N](2-SC5H4N) (9), which is closely related to the active site of [Fe]-hydrogenase, has been prepared unexpectedly via removal of the PMB protecting group from 7 under the action of excess trifluoroacetic acid. The [Fe]-hydrogenase-related complex 9 and its precursor complexes 6 and 7 have been fully characterized by elemental analysis, spectroscopy, and X-ray crystallography.

A Synthetic Pathway to the 1,4-Dihydro-2H-3-benzoxocine System from Morita–Baylis–Hillman Cinnamyl Alcohols with 2,5-Dimethoxy-2,5-dihydrofuran via the Heck Reaction

A new synthetic method for methyl 2-methoxy-1-(meth­oxycarbonylmethyl)-1,4-dihydro-2 H -3-benzoxocine-5-carboxylates was developed using the Heck reaction between 2,5-dimethoxy-2,5-dihydrofuran and methyl 2-(hydroxymethyl)-3-(2-iodophenyl)propenoates as a key step. The latter were readily obtained from the Morita–Baylis–Hillman reaction of iodobenzaldehydes with methyl acrylate through acetylation, rearrangement, and hydrolysis. The methyl 2-methoxy-1-(methoxycarbonylmethyl)-1,4-dihydro-2 H -3-benzoxocine-5-carboxylates were converted into methyl 2-oxo-1,2,5,11b-tetrahydro-3a H -furo[3,2- a ][3]benzoxocine-6-carboxylates on exposure to excess trifluoroacetic acid.

Phosphine Ligands in the Palladium‐Catalysed Methoxycarbonylation of Ethene: Insights into the Catalytic Cycle through an HP NMR Spectroscopic Study

Novel cis-1,2-bis(di-tert-butyl-phosphinomethyl) carbocyclic ligands 6-9 have been prepared and the corresponding palladium complexes [Pd(O(3)SCH(3))(L-L)][O(3)SCH(3)] (L-L=diphosphine) 32-35 synthesised and characterised by NMR spectroscopy and X-ray diffraction. These diphosphine ligands give very active catalysts for the palladium-catalysed methoxycarbonylation of ethene. The activity varies with the size of the carbocyclic backbone, ligands 7 and 9, containing four- and six-membered ring backbones giving more active systems. The acid used as co-catalyst has a strong influence on the activity, with excess trifluoroacetic acid affording the highest conversion, whereas excess methyl sulfonic acid inhibits the catalytic system. An in operando NMR spectroscopic mechanistic study has established the catalytic cycle and resting state of the catalyst under operating reaction conditions. Although the catalysis follows the hydride pathway, the resting state is shown to be the hydride precursor complex [Pd(O(3)SCH(3))(L-L)][O(3)SCH(3)], which demonstrates that an isolable/detectable hydride complex is not a prerequisite for this mechanism.

Formation of Trifluoroacetylated Ephedrine During the Analysis of a Pseudoephedrine-Formaldehyde Adduct by TFAA Derivatization Followed by GC-MS.

(+)-Pseudoephedrine reacts with formaldehyde to form (4S,5S)-3,4-dimethyl-5-phenyloxazolidine. Gas chromatography-mass spectrometry (GC-MS) analysis after the reaction of this oxazolidine with excess trifluoroacetic acid anhydride (TFAA) shows predominantly N,O-bis(trifluoroacetyl)pseudoephedrine with some of the monotrifluoroacetylated derivative. In addition, variable amounts of N,O-bis(trifluoroacetyl)ephedrine were detected by GC-MS. N,O-bis(trifluoroacetyl)ephedrine was not detected upon trifluoroacetylation of the source (+)-pseudoephedrine, and nuclear magnetic resonance analysis of the (4S,5S)-3,4-dimethyl-5-phenyloxazolidine showed no evidence of the (4R,5S) isomer. This suggests that the N,O-bis(trifluoroacetyl)ephedrine is formed by epimerization during the TFAA derivatization and GC-MS analysis of the pseudoephedrine-formaldehyde adduct.

Solvent Control in the Protonation of [Cp*Mo(dppe)H3] by CF3COOH

AbstractThe outcome of the reaction between [Cp*Mo(dppe)H3] [dppe = 1,2‐bis(diphenylphosphanyl)ethane] and trifluoroacetic acid (TFA) is highly dependent on the solvent and the TFA/Mo ratio. The dihydride compound [Cp*Mo(dppe)H2(O2CCF3)] is obtained selectively when the reaction is carried out in aromatic hydrocarbons (benzene, toluene) when using less than one equivalent of TFA. The dihydride is also the end product when THF or MeCN are used as solvent, independent of the TFA/Mo ratio. In benzene/toluene the use of excess acid has a profound effect, resulting in the formation of the tetrahydrido complex [Cp*Mo(dppe)H4]+, which did not further evolve into the dihydrido product. Monitoring of the reaction by NMR and IR spectroscopy under different conditions (solvent, temperature, TFA/Mo ratio) reveals the rapid establishment of an equilibrium between the dihydrogen‐bonded adduct, [Cp*Mo(dppe)H3]···HO2CCF3, the ion‐paired proton‐transfer product, [Cp*Mo(dppe)H4]+···–O2CCF3, and the separated ions, followed by a slower irreversible transformation to the final dihydride product with H2 evolution. The activation parameters of the H2 evolution and M–OR product formation were determined. Excess TFA in low‐polarity solvents stabilizes the separated charged species by forming the homoconjugate anion [CF3COO(CF3COOH)n]–. The effect of the solvent on the course of the reaction can be interpreted in terms of the different polarity, H‐bonding ability, and coordinating power of the various solvent molecules.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Cruciforms as Functional Fluorophores: Response to Protons and Selected Metal Ions

The photophysics of dialkylamino- and/or pyridine-containing functional chromophores, 1,4-distyryl-2,5-bis(ethynylaryl)benzenes (cruciforms) was investigated; their fluorescence quantum yields and emissive lifetimes were determined. Depending upon their substituents, the frontier molecular orbitals (FMOs) of these cruciforms are either congruent, i.e., HOMO and LUMO occupy the same real space, or disjoint, i.e., the HOMO is located on one branch of the cruciform while the LUMO is located on the second one. Donor-acceptor substitution leads to a disjoint FMO pattern, while the parent 1,4-distyryl-2,5-bis(phenylethynyl)benzene shows congruent FMOs. The photophysics of the cruciforms was investigated upon addition of either an excess of trifluoroacetic acid or an excess of selected metal (Mg(2+), Ca(2+), Mn(2+), Zn(2+)) trifluoromethanesulfonate salts. Addition of either metal ions or protons led to analogous but not identical changes in the spectroscopic properties of the investigated cruciforms. The collected data suggest that the metals bind preferentially at the aniline nitrogen and not at the electron-rich arene. The spatially separated FMOs permit the independent manipulation of the HOMO and the LUMO of such cruciforms. If the branches contain metal-complexing moieties, metal binding leads to either a hypsochromic or a bathochromic shift in emission via interaction of the metal cations with either the HOMO or the LUMO.

Novel Cyclo‐Dimerization of 1‐tert‐Butoxycarbonyl‐3‐alkenylindole Derivatives.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Novel cyclo-dimerization of 1- tert-butoxycarbonyl-3-alkenylindole derivatives

Reaction of 1- tert-butoxycarbonyl-3-cyclopentylidenemethyl-1 H-indole with an excess of trifluoroacetic acid in dichloromethane at room temperature gave a cyclic dimer, 13-cyclopentyl-6,7,12,13-tetrahydrospiro[5 H-cyclohepta[1,2- b:4,5- b′]diindole-6,1′-cyclopentane] in 73% yield as the sole product through a novel cyclo-dimerization process. Structure of the cyclic dimer derived from 5-bromo-1- t-butoxycarbonyl-3-cyclopentylidenemethyl-1 H-indole was elucidated by X-ray crystallographic analysis.