Isomers 1a Research Articles

On the geometries, stabilities, and potential energy surfaces of planar C 4B 2 and C 2B 4

The geometrical structures, potential energy surfaces, stabilities, and bonding characteristics of low-energy isomers for planar C 4B 2 and C 2B 4 are systematically investigated at the CCSD(T)/6-311+G(d)//B3LYP/6-311+G(d) level. Isomers 1a ( C 2h , 1 A g ) and 2a ( D 2h , 1 A g ) with belt-like geometries are the lowest-energy structures of C 4B 2 and C 2B 4, respectively, and their structures tend to be similar to those of B 6, CB 5, and C 3B 3 clusters. For C x B 6- x ( x = 1–6) clusters, an interesting planar-to-linear structural transition occurs at x = 1 and 2. The σ-radial, σ-tangential, and delocalized π molecular orbitals are favorable to stabilizing structures of lower-energy isomers of C 4B 2 and C 2B 4 based on the NBO and molecular orbital analyses. The lowest-energy isomers of C 4B 2 and C 2B 4 are stable both thermodynamically and kinetically at the CCSD(T)/6-311+G(d)//B3LYP/6-311+G(d) level and detectable in experiment, which is significant for future experimental studies of C 4B 2 and C 2B 4.

Photoswitching of an alcohol-sensitive photochromic diarylethene

The closed-ring isomer of diarylethene 1a, 1-(2-methyl-5-(4- N, N-diethylaminophenyl)thien-3-yl)-2-(2-methyl-5-phenylthien-3-yl)perfluorocyclopentene was found to cause the substitution reaction with primary alcohols at room temperature. The open-ring isomer 1a was stable in the alcohols. The product obtained in methanol was isolated by HPLC, and the structure was identified by 1H NMR, mass spectrometry, and X-ray crystallographic analysis. It was revealed that two fluorine atoms were replaced with methoxy groups. The substitution reaction was also caused with ethylene glycol to form the five-membered ring. Both the products also showed photochromism, and had absorption maxima and photocycloreversion quantum yields different from those of 1a.

Photoisomerization of 1-Phenyl-2-(pyridin-2-yl)indole BMes2: The Dark Isomer

A new member of photochromic N,C-chelate organoboron compounds, BMes2(Py-N-Ph-In) (1), where Mes = mesityl, Py-N-Ph-In = 1-Ph-2-(2-Py)-indolyl, has been synthesized, and its photo-thermal isomerization properties have been investigated. Upon irradiation by UV light (365 nm), compound 1 isomerizes to compound 1a, changing color from light yellow to dark turquoise-green with the disappearance of the green fluorescence of 1. This process involves the breaking/formation of a B−C bond and a C−C bond and is thermally reversible. Compound 1a finally allowed us to obtain suitable crystals. The crystals of the dark isomer 1a were isolated, and its structure was determined by a single-crystal X-ray diffraction analysis, which confirms the formation of a C−C bond between the indolyl ring and a mesityl ring, the dearomatization of the mesityl ring, and the presence of a BC2 triangle in 1a. NMR and DFT computational data further support that 1a is an analogue of the dark isomers generated from previously reported N,C-chelate BMes2 compounds.

Photochromic and Reductive Electrochemical Switching of a Dithiazolylethene with Large Redox Modulation

A new dipyridylthiazolylethene (1a) and its dicationic analogue (2a), with two N-methylated pyridyl rings, have been synthesized and structurally characterized. Due to the N-methylation of the pyridyl rings, 2 a displays not only very different photochromic properties, but also undergoes a reductive ring-closing reaction to generate its closed-ring isomer 2b. Careful electrochemical studies coupled with EPR spectroscopy show that this reductive ring-closing reaction takes place when 2a is two-electron reduced. DFT calculations suggest that such a ground-state electrocyclization is driven by a very large stabilization of the reduced closed-ring isomer 2b relative to the reduced open-ring isomer 2a. In addition, 2b exhibits two successive and reversible one-electron reductions at half-wave potentials of 0.04 and -0.14 V versus SCE and a redox modulation as large as 1 V is achieved when passing from 2a to 2b.

Synthesis and Structure of 6-Aminofulvene-2-aldiminate Complexes

We report here a synthetic route to bis(N,N'-aryl)-6-aminofulvene-2-aldimine (AFA) ligand systems, specifically Ph(2)-AFAH and Dip(2)-AFAH. The synthesis and structural characterization of a series of Cu(I) complexes [(Ph(2)-AFA)Cu(CNPh)(2)] (2), [(Ph(2)-AFA)Cu(CN(i)Pr)] (3), and [(Dip(2)-AFA)Cu(CN(i)Pr)] (4), from the reaction of the corresponding lithiated AFA systems with Cu-Cl derivatives are reported; notably in the case of [(Ph(2)-AFA)Cu(CNPh)(2)] studies have revealed the existence of two structural isomers (2a and 2b), both of which can be isolated and structurally characterized. Density functional theory (DFT) calculations suggest that the two crystal forms are comparatively close in energy, and geometry optimization reveals a convergence of these two forms to a geometry that more closely resembles the solid-state structure of isomer 2b, having a CH···π interaction. The reactions of the AFA compounds Ph(2)-AFAH and Dip(2)-AFAH with ZnMe(2) and AlMe(3) have also been investigated, and the results of these reactions are described here.

Conformational supramolecular isomerism in one-dimensional silver(i) coordination polymer of a flexible bis(bidentate) N,N-donor ligand with p-xylyl spacer

The isolation and structural characterisation of three isomeric silver(I) complexes, 1a, 1b and 2 with the general formula {[AgL(1)]ClO(4)}(n) (where L(1) is a bis(bidentate) N,N-donor ligand derived from the Schiff-base condensation of α,α'-diamino-p-xylene and pyridine-2-carboxaldehyde) are discussed. Single-crystal X-ray structures reveal the polymeric nature for the complexes where all the silver ions are in pseudotetrahedral geometry with the AgN(4) coordination environment. Isomers 1a (Pc space group) and 1b (Cc space group) were crystallised from acetonitrile whereas 2 (C2/c space group) was crystallised during the synthesis from a solvent mixture of dicholormethane and methanol. The flexible ligand (L(1)) adopts only an anti conformation in 1b and the presence of two different anti conformations in the repeating unit results in the formation of a trapezoidal wave polymeric chain. However, both gauche and anti conformations of the ligand are found to be present in the polymeric chains of 1a. In the polymeric chain of 2, only one anti isomer of the ligand is present in the repeating unit resulting in a triangular wave chain. The structure of isomer 1a is solvent induced and solvent plays a major role in the crystal packing of this isomer. One-dimensional coordination polymers 1a, 1b and 2 are related to each other as conformational supramolecular isomers. Additionally, two independent polymeric chains parallel to each other: one triangular wave consisting of only an anti conformation and a trapezoidal wave chain consisting of alternate gauche and anti conformations of the ligand are observed in 1a. This is a rare example of two supramolecular isomers present in the same crystal. Six different conformers of the flexible ligand are observed in the crystals of coordination polymers.

Dehydro[12]annulenes: Structures, Energetics, and Dynamic Processes

Density functional and coupled cluster calculations on neutral monodehydro[12]annulenes (C(12)H(10)) reveal a global minimum that should be kinetically stable. At the CCSD(T)/cc-pVDZ//BHLYP/6-31G* level, the unsymmetrical CTCTC conformer 1a lies at least 3 kcal/mol below all other isomers studied. The two isomers closest in energy to 1a are Möbius structure 5a (CCTCC) and all-cis 6a. Isomer 1a can undergo conformational automerization with E(a) = 3.9 kcal/mol, implying that this process would be rapid on the NMR time scale, and computed (1)H NMR parameters (GIAO-B3LYP/6-311+G**//RHF/6-31G*) are presented. Cumulenic dehydro[12]annulene isomers, with 1,2,3-butatriene subunits, were found to be reactive intermediates in the interconversion of different configurations of the alkyne forms. Pathways for configuration change of 1a, and for subsequent rearrangement to biphenyl, were investigated. The 28 kcal/mol overall barrier for the lowest energy pathway connecting 1a to biphenyl suggests that 1a is kinetically stable with respect to valence isomerization.

A theoretical study on structures, stabilities, and potential energy surfaces of planar BnP2 (n = 1–7)

The geometries, stabilities, and potential energy surfaces of possible isomers of BnP2 (n=1–7) are explored and investigated at the CCSD(T)/6-311+G(d)//B3LYP/6-311+G(d) level. Many planar structures for the possible isomers of BnP2 (n=1–7) and transition states are located. The lowest-energy structures (1a–7a) of BnP2 exhibit belt-like growth feature with two phosphorus atoms capped to two terminal B-B edges of Bn unit. The lowest-energy structures B2P2(2a), B4P2(4a), and B6P2(6a) are more stable than their neighbors. Especially, the lowest-energy isomer (4a) of B4P2 has exceptional stability. Results from molecular orbital analysis suggest that the formation of the delocalized π, the σ-radial, and σ-tangential MOs is favorable to stabilizing the structures of lowest-energy isomers (1a–7a) of BnP2. In addition, results from molecular orbital and nucleus independent chemical shift demonstrate that BP2 and B7P2 may have aromaticity. Importantly and interestingly, the lowest-energy isomers (2a, 3a, 4a, 5a, and 6a) of BnP2 (n=2–6) are stable both thermodynamically and kinetically at the CCSD(T)/6-311+G(d)//B3LYP/6-311+G(d) level and may be observable in laboratory, which is helpful for further experimental studies of BnP2.

Optically Activated Uptake and Release of Cu2+ or Ag+ Ions by or from a Photoisomerizable Monolayer-Modified Electrode

Di-(N-butanoic acid-1,8-naphthalimide)-piperazine dithienylethene was covalently linked to a cysteamine monolayer associated with a Au surface to yield a photoisomerizable monolayer composed of the open or closed dithienylcyclopentene isomers (3a or 3b), respectively. Electrochemical and XPS analyses reveal that the association of metal ions to the monolayer is controlled by its photoisomerization state. We find that Cu(2+) ions reveal a high affinity for the open (3a) monolayer state, K(a) = 4.6 × 10(5) M(-1), whereas the closed monolayer state (3b) exhibits a substantially lower binding affinity for Cu(2+), K(a) = 4.1 × 10(4) M(-1). Similarly, Ag(+) ions bind strongly to the 3a monolayer state but lack binding affinity for the 3b state. The reversible photoinduced binding and dissociation of the metal ions (Cu(2+) or Ag(+)) with respect to the photoisomerizable monolayer are demonstrated, and the systems may be used for the photochemically controlled uptake and release of polluting ions. Furthermore, we demonstrate that the photoinduced reversible binding and dissociation of the metal ions to and from the photoisomerizable electrode control the wettability properties of the surface.

Inhibition of P-glycoprotein-mediated Multidrug Resistance (MDR) by N,N-bis(cyclohexanol)amine aryl esters: Further restriction of molecular flexibility maintains high potency and efficacy

Conformational modulation of the aryl portion of a set of N,N-bis(cyclohexanol)amine aryl esters (1a–d) that are potent Pgp-dependent MDR inhibitors has been performed. Toward this end the trans-3-(3,4,5-trimethoxyphenyl)acrylic acid present in set 1 was substituted with 3-(3,4,5-trimethoxyphenyl)propanoic and 3-(3,4,5-trimethoxyphenyl)propiolic moieties to give sets 2 and 3, respectively. While the introduction of 3-(3,4,5-trimethoxyphenyl)propanoic moiety resulted in a definite drop in potency and efficacy, esterification with 3-(3,4,5-trimethoxyphenyl)propiolic acid gave four isomers (3a–d) that maintain high potency and possess optimal efficacy. These results are discussed in terms of conformational flexibility of the different sets of compounds.

Reactions of group 13 metal trialkyls with oxamides

Alkyl aluminum-, gallium-, and indium oxamidates Me 4Al 2(dpoa) ( 1), Me 4Al 2(dboa) ( 2), Me 4Ga 2(dpoa) ( 3), Me 4Ga 2(dboa) ( 4), t Bu 4Ga 2(dpoa) ( 5) and Me 4In 2(dboa) ( 6) (dpoa-H 2 = N, N′-diphenyloxamide, dboa-H 2 = N, N′-di- tert-butyloxamide) have been prepared and characterized. Compounds 1– 3, 5 and 6 exist in the form of isomers a only, with a skeleton framework of the molecules consisting of two almost flat, coplanar and fused MNOC 2 (M = Al, Ga, In) heterocyclic rings. Depending on the reaction conditions, the compound 4 was obtained as the isomer 4a or as the mixture of two isomers 4a and 4b. Molecular structures of the compounds 1a– 6a have been determined by X-ray crystallography. A structure of the isomer 4b was proposed on the basis of NMR spectroscopy. A skeleton framework of the 4b molecule consists of two fused different cycles, GaO 2C 2 and GaN 2C 2.

Triphenylantimony(V) o‐amidophenolates with unsymmetrical N‐aryl group for a reversible dioxygen binding

AbstractNew triphenylantimony(V) o‐amidophenolates (AP‐Me,Et)SbPh3 (1) and (AP‐Me,iPr)SbPh3 (2) with unsymmetrically substituted N‐aryl groups and (AP‐Et,Et)SbPh3 (3) with symmetrical N‐aryl group {AP‐R1,R2 is 4,6‐di‐tert‐butyl‐N‐[2‐alkyl(R1),6‐alkyl(R2)‐phenyl]‐o‐amidophenolate dianion} were synthesized and characterized in detail. Complexes were examined for dioxygen activity. The unsymmetrical complexes 1 and 2 were found to form different geometrical isomers (A and B) of spiroendoperoxides [L‐R1,R2(O2)]SbPh3 (4 and 5, respectively) with different dispositions of peroxide group and N‐aryl fragment (methyl and peroxide group are on the same side of the molecule in the less shielded isomer A, and on different sides in the more hindered isomer B). The isomer A prevails over isomer B, reflecting the possibility of steric control on the dioxygen‐binding reaction. Complex 3, where R1 = R2 = Et, formed the isomers 6A and 6B as 50:50. The ratio 4A:4B was 60:40 (for methyl‐ethyl containing complex 4) and it increased up to 80:20 for methyl‐isopropyl‐containing 5. The molecular structure of isomers 4A and 4B was confirmed by X‐ray analysis. Copyright © 2010 John Wiley & Sons, Ltd.

Diphenyl(1-naphthyl)phosphine Ancillary for Assembling of Red and Orange-Emitting Ir(III) Based Phosphors; Strategic Synthesis, Photophysics, and Organic Light-Emitting Diode Fabrication

Treatment of a series of dinuclear Ir(III) complexes [(fnazo)(2)Ir(μ-Cl](2), [(fpiq)(2)Ir(μ-Cl](2), and [(fppy)(2)Ir(μ-Cl](2) with diphenyl(1-naphthyl)phosphine (dpnH) in decalin at 100 °C afforded the simple adducts, trans-N,N'-[(fnazo)(2)Ir(dpnH)Cl] (1a), trans-N,N'-[(fpiq)(2)Ir(dpnH)Cl] (1b), and trans-N,N'-[(fppy)(2)Ir(dpnH)Cl] (1c), for which the C(∧)N cyclometalating reagents, that is, fnazoH, fpiqH and fppyH, stands for 4-(4-fluorophenyl)quinazoline, 1-(4-fluorophenyl)isoquinoline and 4-fluorophenylpyridine, respectively. Single crystal X-ray diffraction study on 1a revealed existence of two trans-N,N' cyclometalates, with both chloride and dpnH donors located at the positions opposite to the phenyl substituents. Subsequent heating of 1a-1c at higher temperature afforded the second isomer (2a-2c), showing formation of cis-N,N' orientation for the aforementioned cyclometalates. Further thermolysis of either trans or cis-Ir(III) complexes 1 or 2 in presence of sodium acetate, which serves as both activator and chloride scavenger, gave successful isolation of a mixture of two fully cyclometalated Ir(III) complexes trans-N,N'-[(C(∧)N)(2)Ir(dpn)] (3a-3c) and cis-N,N'-[(C(∧)N)(2)Ir(dpn)] (4a-4c). Structural and photophysical properties of complexes 3a-3c and 4a-4c were measured and compared. Time-dependent density functional theory (DFT) studies suggested that, upon changing the C(∧)N cyclometalates from quinazolinyl, isoquinolinyl, and, finally, to pyridyl fragment, the lowest unoccupied molecular orbitals (LUMOs) are gradually shifted from the cyclometalating nitrogen heterocycles to the 1-naphthyl group of the phosphine chelate and, concomitantly altered the photophysical properties. An organic light-emitting diode (OLED) using orange-red phosphors 4a and 4b has been successfully fabricated. At the practical brightness of 500 cd·m(-2), decent external quantum efficiency of 10.6% and 12.5% could be reached for 4a and 4b, respectively, revealing the usefulness of relevant molecular architecture in designing triplet OLED emitters.

ChemInform Abstract: Cycloaddition-Elimination Reactions of 4-Methyl-5-phenylimino-δ2- 1,2,3,4-thiatriazoline with Electrophilic Nitriles.

4-Methyl-5-phenyliminothiatriazoline 4 undergoes two consecutive cycloaddition-elimination reactions with ethyl cyanoformate and p-toluenesulfonyl cyanide in refluxing chloroform, and yields the 1,2,4-thiadiazolines 6a,b via the isomers 5a,b. In acetone as the solvent, the reactions occur at room temperature, due to the formation of the 1,2,4-oxathiazolidine 12 as the intermediate. When trichloroacetonitrile was used, only the decomposition products of 4, namely 7 and 8 were obtained.

ChemInform Abstract: Mammalian Alkaloids: Synthesis and O-Methylation of (S)- and (R)-3′- Hydroxycoclaurine and Their N-Methylated Analogues with S-Adenosyl-L-( methyl-14C)methionine in Presence of Mammalian Catechol O- Methyltransferase.

O-Methylation of the optically active 3′-hydroxycoclaurines 3a and 3b and of the N-methylated analogs 5a,b with S-adenosyl-L-[methyl-14C]methionine in presence of mammalian COMT was investigated in vitro. The N-unsubstituted (1S)- and (1R )-isomers 3a and 3b, respectively, afforded almost equal amounts of the corresponding N-norreticuline 4 and N-nororientaline 19, besides two unknown by-products (see Fig. and Table 1). The N-methylated (1S)-isoquinoline 5a, on the other hand, afforded largely (S)-orientaline ((S)-19), while an almost equal mixture of (R)-reticuline (6b) and (R)-orientaline ((R)-19) was obtained from the (1R)-enantiomer 5b. The isoquinolines 3a,b and 5a,b were prepared by a Bischler-Napieralski cyclization yielding O-benzyl-protected isoquinoline 10 (Scheme 1). The optical resolution of 10 was accomplished with 2′-bromotartranilic acid. The N-methylated isoquinolines were prepared by N-formylation of 10a,b and reduction of the formamides 13a,b with diborane ( 14a,b). Deblocking of the benzyl-ether moieties of 10a,b and 14a,b was accomplished by catalytic hydrogenation in presence of HCl, affording directly 3a,b·HCl and 5a,b·HCl, respectively.

ChemInform Abstract: Isolation of an Isomer of FK-506 from Fermentation of Streptomyces tsukubaensis and Its Chemical Synthesis from FK-506.

Abstract From the fermentation broth of Streptomyces tsukubaensis 9993 an isomer 2a of the immunosuppressant FK-506 1a was isolated as a minor metabolite. From NMR- and FAB-MS data follows that in 2a the size of the macrocycle is reduced by two carbon atoms due to a shift of the lactone-acyl from 0–26 to 0–24. The compound was synthesized from FK-506 and proved to be identical with the natural product 2a.

ChemInform Abstract: Oxidation of Spiroketones with DDQ - Synthesis of Tropone Derivatives and DDHQ Diesters.

Abstract Oxidation of spiroketones 3a–f with DDQ in dry benzene gave tropone derivatives 4a–f and DDHQ esters 5a–f ( cis - cis isomer 6a–f, trans - trans isomer 7a–f). While the aryl substituted spirokeone 17a gave a 2:1 mixture of 19a and the corresponding trans - trans isomer, the aryl substituted spiroketones 17b–d gave exclusively cis - cis isomers 19b–d. Heating acid chloride of acid 9c with DDHQ resulted in compounds 4a and 7a, thus confirming the structures assigned. Mechanism of formation of these compounds has been rationalised. A detailed study of 2D 1H-1H COSY, 1H-13C COSY, HMBC and 2D NOESY of compound 7d led to complete assignment of 1H and 13C NMR signals and its solution conformation.

ChemInform Abstract: Photocycloaddition of Deoxyuridines to 2,3-Dimethyl-2-butene.

Direct and ketone (acetone or acetophenone)-sensitized photocycloaddition of 2,3-dimethyl-2-butene to 2′-deoxyuridine (1a), thymidine (1b), 5-fluoro-2′-deoxyuridine (1c), and their 3′,5′-di-O-acetyl derivatives 1d—1f by near-UV irradiation have been studied. The triplet excited state of the nucleosides was found to be the major intermeidate by the triplet quenching technique. From the respective reactants, a pair of diastereomeric products having a cyclobutane ring were isolated. The absolute configuration of the bridgehead carbon atoms was identified by X-ray crystallographic analyses with two of them as (1R, 6R)-isomer 3a and (1S, 6S)-isomer 2b and by 1H NMR. The conformations of the glycosyl bond, the pyrimidine ring, and the sugar portion in solution were identified by 1H NMR and compared with the ones in the crystalline state.

Carbon dioxide and water as a key for unlocking photochromism of diarylethene derivative

A photochromic diarylethene derivative with 4-(ethylideneamino) phenol group ( 1a) is prepared, and 1a exhibits ring-opening and ring-closing photoisomerization with UV/vis light irradiation in solution. Addition of base to both solution of ring-open isomer 1a and ring-closed isomer 1b produces deprotonated compounds 2a and 2b, respectively, and both 2a and 2b are photo-inactive and no photochemical reaction is detected in solution in the absence of carbon dioxide and water. Both 2a and 2b are, however, converted back to 1a and 1b when the solution contains carbon dioxide and water, and photochromic reaction is recovered. This may provide a means to generate a gate for non-destructive readout. Meanwhile, the conversion between species is accompanied color change in a wide range by combination of photo-trigger and chemical trigger. The system endowed with multi-responsive functionality for multi-color change is beneficial for applications such as display and camouflage.

Search for structures, potential energy surfaces, and stabilities of planar BnP(n = 1 ∼ 7)

We have systematically explored and investigated the geometrical structures, stability, growth pattern, bonding character, and potential energy surface (PES) of the possible isomers of each cluster for planar B(n)P (n = 1 ∼ 7) at the CCSD(T)/6-311+;G(d)//B3LYP/6-311+G(d) level. A large number of planar structures for the possible isomers of B(n)P (n = 1 ∼ 7) and transition states are located. Isomers 1a ∼ 7a of B(n)P are the lowest-energy structures and 2a, 4a, as well as 6a are more stable than their neighbors. For the lowest-energy structures (1a ∼ 7a) of B(n)P, P atom lies at the apex and tends to form two B-P bonds with boron atoms. They exhibit planar zigzag growth feature or approximately spherical-like growth pattern. Results from molecular orbital analysis demonstrate that the formation of the delocalized π MOs and the σ-radial and σ-tangential MOs plays a critical role in stabilizing the structures of lowest-energy isomers (2a ∼ 7a) of B(n)P. Importantly, isomers 3a, 3c, 3d, 4a, 4b, 5b, and 5c of B(n)P are stable both thermodynamically and kinetically at the CCSD(T)/6-311+G(d)// B3LYP/6-311+G(d) level and detectable in laboratory, which is valuable for further experimental studies of B(n)P.