New Syntheses of Retinal and Its Acyclic Analog γ‐Retinal by an Extended Aldol Reaction with a C6 Building Block That Incorporates a C5 Unit after Decarboxylation. A Formal Route to Lycopene and β‐Carotene

Since the C₁₅ β‐end‐group aldehyde 10 ((β‐ionylidene)acetaldehyde), an excellent intermediate in the syntheses of retinoids, can be synthesized in many ways from β‐ionone, and since the corresponding acyclic C₁₅ ψ‐end‐group aldehyde 5 can easily be synthesized from citral ( 1 ) (Scheme 3), we applied the C₁₅+C₅ route to the syntheses of γ‐retinal ((all‐E)‐ 8 ) (Scheme 3) and retinal ((all‐E)‐ 13 ) (Scheme 4), and therefore, by coupling (2×C₂₀→C₄₀), to the preparation of lycopene ( 14 ) and β‐carotene ( 15 ) (Scheme 5). Our new syntheses of retinal ((all‐E)‐ 13 ) and γ‐retinal ((all‐E)‐ 8 use an extended aldol reaction with a C₆ building block that incorporates a C₅ unit after decarboxylation.     

Comparison of the structure of (E)‐2‐(2‐benzylidenehydrazinylidene)quinoxaline with those of its chloro‐ and bromobenzylidene analogues

(E)‐2‐(2‐Benzylidenehydrazinylidene)quinoxaline, C₁₅H₁₂N₄, crystallized with two molecules in the asymmetric unit. The structures of six halogen derivatives of this compound were also investigated: (E)‐2‐[2‐(2‐chlorobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁ClN₄; (E)‐2‐[2‐(3‐chlorobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁ClN₄; (E)‐2‐[2‐(4‐chlorobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁ClN₄; (E)‐2‐[2‐(2‐bromobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁BrN₄; (E)‐2‐[2‐(3‐bromobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁BrN₄; (E)‐2‐[2‐(4‐bromobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁BrN₄. The 3‐Cl and 3‐Br compounds are isomorphous, as are the 4‐Cl and 4‐Br compounds. In all of these compounds, it was found that the supramolecular structures are governed by similar predominant patterns, viz. strong intermolecular N—H...N(pyrazine) hydrogen bonds supplemented by weak C—H...N(pyrazine) hydrogen‐bond interactions in the 2‐ and 3‐halo compounds and by C—H...Cl/Br interactions in the 4‐halo compounds. In all compounds, there are π–π stacking interactions.     

The Astounding Chemistry of a 2‐Amino‐1,2‐dihydroisoquinoline Derivative

The cycloadducts of isoquinolinium N‐phenyl imide 2 with C=C bonds are derivatives of 2‐amino‐1,2‐dihydroisoquinoline. Their N^β‐vinylphenylhydrazine system is amenable to an acid‐catalyzed [3,3]‐sigmatropic shift; the formation of pentacyclic aminals is exemplified by 6 → 8 . The dimethyl maleate adduct 11 , C₂₁H₂₀N₂O₄, is exceptional by being converted on treatment with acid to bright‐yellow crystals, C₂₄H₂₂N₂O₆ (additional C₃H₂O₂). X‐Ray crystal‐structure analysis and NMR spectra reveal structure 13 , and mechanistic studies indicated an initial β‐elimination at the N−N bond of 11 to yield 18 ; this step is followed by a retro‐Mannich‐type cleavage that gives methyl isoquinoline‐1‐acetate ( 14 ) and methyl 2‐(phenylimino)acetate ( 15 ), according to the sequence C₂₁H₂₀N₂O₄ ( 11 )→ 18 →C₁₂H₁₁NO₂ ( 14 )+C₉H₉NO₂ ( 15 ). In the second act of the drama, electrophilic attack by 15 ‐H⁺ on the ene‐hydrazine group of a second molecule of 11 furnishes 13 by a polystep intramolecular redox reaction. All rate constants must be fine‐tuned in this reaction cascade to give 13 in yields of up to 78% with an overall stoichiometry: 2 C₂₁H₂₀N₂O₄ ( 11 )→C₂₄H₂₂N₂O₆ ( 13 )+C₁₂H₁₁NO₂ ( 14 )+aniline. Interception and model experiments confirmed the above pathway. A by‐product, C₃₃H₃₁N₃O₆ ( 62 ), arises from an acid‐catalyzed dimerization of 11 and subsequent elimination of 15 .     

4‐(4‐Chlorobenzylidenehydrazonomethyl)benzonitrile and the bromo and iodo analogs

4‐Cyano‐4′‐chlorobenzalazine [systematic name: 4‐(4‐chlorobenzylidenehydrazonomethyl)benzonitrile], C₁₅H₁₀ClN₃, occurs in two polymorphs. Polymorph A is isostructural with the corresponding dichloro compound. Polymorph B is isostructural with the bromo and iodo analogs, viz. C₁₅H₁₀BrN₃ and C₁₅H₁₀IN₃, respectively. The latter three structures all have approximately linear C—N...X—C intermolecular contacts in which the N...X contact distances are longer than those in the corresponding benzylideneanilines.     

Hydrogen bonding in cyclic imides and amide carboxylic acid derivatives from the facile reaction of cis‐cyclohexane‐1,2‐carboxylic anhydride with o‐ and p‐anisidine and m‐ and p‐aminobenzoic acids

The structures of the open‐chain amide carboxylic acid rac‐cis‐2‐[(2‐methoxyphenyl)carbamoyl]cyclohexane‐1‐carboxylic acid, C₁₅H₁₉NO₄, (I), and the cyclic imides rac‐cis‐2‐(4‐methoxyphenyl)‐3a,4,5,6,7,7a‐hexahydroisoindole‐1,3‐dione, C₁₅H₁₇NO₃, (II), chiral cis‐3‐(1,3‐dioxo‐3a,4,5,6,7,7a‐hexahydroisoindol‐2‐yl)benzoic acid, C₁₅H₁₅NO₄, (III), and rac‐cis‐4‐(1,3‐dioxo‐3a,4,5,6,7,7a‐hexahydroisoindol‐2‐yl)benzoic acid monohydrate, C₁₅H₁₅NO₄·H₂O, (IV), are reported. In the amide acid (I), the phenylcarbamoyl group is essentially planar [maximum deviation from the least‐squares plane = 0.060 (1) Å for the amide O atom] and the molecules form discrete centrosymmetric dimers through intermolecular cyclic carboxy–carboxy O—H...O hydrogen‐bonding interactions [graph‐set notation R₂²(8)]. The cyclic imides (II)–(IV) are conformationally similar, with comparable benzene ring rotations about the imide N—C_ar bond [dihedral angles between the benzene and isoindole rings = 51.55 (7)° in (II), 59.22 (12)° in (III) and 51.99 (14)° in (IV)]. Unlike (II), in which only weak intermolecular C—H...O_imide hydrogen bonding is present, the crystal packing of imides (III) and (IV) shows strong intermolecular carboxylic acid O—H...O hydrogen‐bonding associations. With (III), these involve imide O‐atom acceptors, giving one‐dimensional zigzag chains [graph‐set C(9)], while with the monohydrate (IV), the hydrogen bond involves the partially disordered water molecule which also bridges molecules through both imide and carboxy O‐atom acceptors in a cyclic R₄⁴(12) association, giving a two‐dimensional sheet structure. The structures reported here expand the structural database for compounds of this series formed from the facile reaction of cis‐cyclohexane‐1,2‐dicarboxylic anhydride with substituted anilines, in which there is a much larger incidence of cyclic imides compared to amide carboxylic acids.     

Nine closely related tetrahydro‐1,4‐epoxy‐1‐benzazepines carrying pendant heterocyclic substituents: hydrogen‐bonded supramolecular assembly in zero,one and two dimensions

The structures are reported of nine closely related tetrahydro‐1,4‐epoxy‐1‐benzazepines carrying pendant heterocyclic substituents, namely: 2‐exo‐(5‐nitrofuran‐2‐yl)‐2,3,4,5‐tetrahydro‐1,4‐epoxy‐1H‐1‐benzazepine, C₁₄H₁₂N₂O₄, (I), 7‐fluoro‐2‐exo‐(1‐methyl‐1H‐pyrrol‐2‐yl)‐2,3,4,5‐tetrahydro‐1,4‐epoxy‐1H‐1‐benzazepine, C₁₅H₁₅FN₂O, (II), 7‐fluoro‐2‐exo‐(5‐methylfuran‐2‐yl)‐2,3,4,5‐tetrahydro‐1,4‐epoxy‐1H‐1‐benzazepine, C₁₅H₁₄FNO₂, (III), 7‐fluoro‐2‐exo‐(3‐methylthiophen‐2‐yl)‐2,3,4,5‐tetrahydro‐1,4‐epoxy‐1H‐1‐benzazepine, C₁₅H₁₄FNOS, (IV), 7‐fluoro‐2‐exo‐(5‐methylthiophen‐2‐yl)‐2,3,4,5‐tetrahydro‐1,4‐epoxy‐1H‐1‐benzazepine, C₁₅H₁₄FNOS, (V), 7‐chloro‐2‐exo‐(5‐methylfuran‐2‐yl)‐2,3,4,5‐tetrahydro‐1,4‐epoxy‐1H‐1‐benzazepine, C₁₅H₁₄ClNO₂, (VI), 2‐exo‐(5‐methylfuran‐2‐yl)‐7‐trifluoromethoxy‐2,3,4,5‐tetrahydro‐1,4‐epoxy‐1H‐1‐benzazepine, C₁₆H₁₄F₃NO₃, (VII), 2‐exo‐(3‐methylthiophen‐2‐yl)‐7‐trifluoromethoxy‐2,3,4,5‐tetrahydro‐1,4‐epoxy‐1H‐1‐benzazepine, C₁₆H₁₄F₃NO₂S, (VIII), and 2‐exo‐(5‐nitrofuran‐2‐yl)‐7‐trifluoromethoxy‐2,3,4,5‐tetrahydro‐1,4‐epoxy‐1H‐1‐benzazepine, C₁₅H₁₁F₃N₂O₅, (IX). All nine compounds crystallize in centrosymmetric space groups as racemic mixtures with configuration (2RS,4SR). There are no direction‐specific interactions between the molecules in (V). The molecules in (III), (IV), (VI) and (VII) are linked into simple chains, by means of a single C—H...O hydrogen bond in each of (III), (VI) and (VII), and by means of a single C—H...π(arene) hydrogen bond in (IV), while the molecules in (VIII) are linked into a chain of rings. In each of (I) and (II), a combination of one C—H...O hydrogen bond and one C—H...π(arene) hydrogen bond links the molecules into sheets, albeit of completely different construction in the two compounds. In (IX), the sheet structure is built from a combination of four independent C—H...O hydrogen bonds and one C—H...π(arene) hydrogen bond. Comparisons are made with some related compounds.     

Hirshfeld surface analysis of two bendroflumethiazide solvates

Bendroflumethiazide, or 3‐benzyl‐6‐(trifluoromethyl)‐3,4‐dihydro‐2H‐1,2,4‐benzothiadiazine‐7‐sulfonamide 1,1‐dioxide, is reported to crystallize as 1:1 solvates with acetone, C₁₅H₁₄F₃N₃O₄S₂·C₃H₆O, and N,N‐dimethylformamide, C₁₅H₁₄F₃N₃O₄S₂·C₃H₇NO. A detailed investigation of the crystal packing and intermolecular interactions is presented by means of Hirshfeld surface analysis. This analysis confirms the atomic positions of methyl H atoms of the solvent molecules that were inferred from the X‐ray data and provides a useful tool for structure validation.     

7‐{Di­phenyl­[(tri­phenyl­phos­phine)­aurio]­phos­phine(1+)‐P}‐8‐methyl‐7,8‐dicarba‐nido‐undecaborate(1–) dichloro­methane hemi­solvate

The title compound, 7‐[(Ph₂P)Au(PPh₃)]‐8‐(CH₃)‐7,8‐nido‐C₂B₉H₁₀]·­0.5CH₂Cl₂ or [Au(C₁₅H₂₃B₉P)­(C₁₈H₁₅P)]·­0.5CH₂Cl₂, is the first reported gold derivative of the ligand [7‐­(Ph₂P)‐8‐(CH₃)‐7,8‐nido‐C₂B₉H₁₀]^?. It has a mono­nuclear structure with the gold centre in an essentially linear coordination [P—Au—P 174.041 (15)°]. The open C₂B₃ face contains one H atom that is strongly bonded to the central B atom and semi‐bridging to a neighbouring B atom [B—H distances 1.070 (16) and 1.45 (3) Å].     

Supramolecular networks of 10‐(2‐hydroxyethyl)acridin‐9(10H)‐one and 10‐(2‐chloroethyl)acridin‐9(10H)‐one

Both 10‐(2‐hydroxyethyl)acridin‐9(10H)‐one, C₁₅H₁₃NO₂, and 10‐(2‐chloroethyl)acridin‐9(10H)‐one, C₁₅H₁₂ClNO, have monoclinic (P2₁/c) symmetry and supramolecular three‐dimensional networks. But the differences in the intermolecular interactions displayed by the hydroxy group and the chlorine substituent lead to stronger intermolecular π‐stacking interactions and hydrogen bonding, and hence a significantly higher melting point for the former.     

(±)‐6‐Benzyl‐3,3‐di­methyl­morpholine‐2,5‐dione and its 5‐mono­thio and 2,5‐di­thio derivatives

The morpholine ring of the title dione, C₁₃H₁₅NO₃, shows a boat conformation that is distorted towards a twist‐boat, with the boat ends being the two Csp³ atoms of the ring. The benzyl substituent is in the favoured `exo' position. In the mono­thione derivative, (±)‐6‐benzyl‐3,3‐di­methyl‐5‐thioxo­morpholin‐2‐one, C<sub>13</sub>H<sub>15</sub>NO<sub>2</sub>S, this ring has a much flatter conformation that is midway between a boat and an envelope, with the di­methyl end being almost planar. The orientation of the benzyl group is `endo'. The di­thione derivative, (±)‐6‐benzyl‐3,3‐di­methyl­morpholine‐2,5‐di­thione, C₁₃H₁₅N­OS₂, has two symmetry‐independent mol­ecules, which show different puckering of the morpholine ring. One mol­ecule has a flattened envelope conformation distorted towards a screw‐boat, while the conformation in the other mol­ecule is similar to that in the mono­thione derivative. Intermolecular hydrogen bonds link the mol­ecules in the three compounds, respectively, into centrosymmetric dimers, infinite chains, and dimers made up of one of each of the symmetry‐independent mol­ecules.     

Halogenated C,N‐diarylacetamides: molecular conformations and supramolecular assembly

The structures of four halogenated N,2‐diarylacetamides are reported and compared with a range of analogues. N‐(4‐Chloro‐3‐methylphenyl)‐2‐phenylacetamide, C₁₅H₁₄ClNO, (I), and N‐(4‐bromo‐3‐methylphenyl)‐2‐phenylacetamide, C₁₅H₁₄BrNO, (II), are isostructural in the space group P. The molecules of (I) and (II) are linked into chains of rings by a combination of N—H...O and C—H...π(arene) hydrogen bonds. The molecules of N‐(4‐chloro‐3‐methylphenyl)‐2‐(2,4‐dichlorophenyl)acetamide, C₁₅H₁₂Cl₃NO, (III), and N‐(4‐bromo‐3‐methylphenyl)‐2‐(2‐chlorophenyl)acetamide, C₁₅H₁₃BrClNO, (IV), are linked into simple C(4) chains by N—H...O hydrogen bonds, but significant C—H...π(arene) interactions are absent. The N‐aryl groups in compounds (III) and (IV) adopt a different orientation, by ca 180°, from that of the corresponding groups in compounds (I) and (II), but otherwise the conformations of (I)–(IV) are very similar. Comparisons are drawn between compounds (I) and (IV) and a range of analogues of the type R¹CH₂CONHR², where R² represents a halogenated aryl ring and R¹ represents either another halogenated aryl ring or a naphthalen‐1‐yl unit.     

Four cytotoxic N4‐substituted thiosemicarbazones derived from 2‐hydroxynaphthalene‐1‐carboxaldehyde

The X‐ray crystal structures are reported of four novel and potentially O,N,S‐tridentate donor ligands that demonstrate antitumour activity. These ligands are 1‐[(4‐methyl­thio­semicarbazono)methyl]‐2‐naphthol, C₁₃H₁₃N₃OS, (III), 1‐[(4‐ethylthio­semicarbazono)­methyl]‐2‐naphthol, C₁₄H₁₅N₃OS, (IV), 1‐[(4‐phenyl­thio­semicarbazono)­methyl]‐2‐naphthol, C₁₈H₁₅N₃OS, (V), and 1‐[(4,4‐di­methyl­thio­semicarbazono)­methyl]‐2‐naphthol di­methyl sulfoxide solvate, C₁₄H₁₅N₃OS·C₂H₆OS, (VI). These chelators are N4‐substituted thio­semicarbazones, each based on the same parent aldehyde, namely 2‐­zhydroxynaphthalene‐1‐carboxaldehyde isonicotinoylhydrazone. Conformational variations within this series are discussed in relation to the optimum conformation for metal‐ion binding.     

Four 7‐aryl‐substituted pyrido[2,3‐d]pyrimidine‐2,4(1H,3H)‐diones: similar molecular structures but different crystal structures

Molecules of 1,3‐dimethyl‐7‐(4‐methylphenyl)pyrido[2,3‐d]pyrimidine‐2,4(1H,3H)‐dione, C₁₆H₁₅N₃O₂, (I), are linked by paired C—H...O hydrogen bonds to form centrosymmetric R₂²(10) dimers, which are linked into chains by a single π–π stacking interaction. A single C—H...O hydrogen bond links the molecules of 7‐(biphenyl‐4‐yl)‐1,3‐dimethylpyrido[2,3‐d]pyrimidine‐2,4(1H,3H)‐dione, C₂₁H₁₇N₃O₂, (II), into C(10) chains, which are weakly linked into sheets by a π–π stacking interaction. In 7‐(4‐fluorophenyl)‐3‐methylpyrido[2,3‐d]pyrimidine‐2,4(1H,3H)‐dione, C₁₄H₁₀FN₃O₂, (III), an N—H...O hydrogen bond links the molecules into C(6) chains, which are linked into sheets by a π–π stacking interaction. The molecules of 7‐(4‐methoxyphenyl)‐3‐methylpyrido[2,3‐d]pyrimidine‐2,4(1H,3H)‐dione, C₁₅H₁₃N₃O₃, (IV), are also linked into C(6) chains by an N—H...O hydrogen bond, but here the chains are linked into sheets by a combination of two independent C—H...π(arene) hydrogen bonds.     

Charge‐transfer complexes of N‐methyl‐, N‐iso­propyl‐, N‐butyl‐ and N‐iso­butyl­carbazole with 3,5‐di­nitro­benzoic acid

In the title four compounds, C₁₃H₁₁N·C₇H₄N₂O₆, (I), C₁₅H₁₅N·C₇H₄N₂O₆, (II), C₁₆H₁₇N·C₇H₄N₂O₆, (III), and C₁₆H₁₇N·C₇H₄N₂O₆, (IV), the donor and acceptor mol­ecules are stacked alternately to form one‐dimensional columns. In (I), the N‐methyl group of the donor is nearly eclipsed with respect to one of the nitro groups of the neighboring acceptor in a column, whereas the N‐iso­propyl, N‐butyl and N‐iso­butyl groups are in anti positions with respect to one of the nitro groups of the neighboring acceptor in compounds (II)–(IV).     

Crystallization experiments with the dinuclear chelate ring complex di‐μ‐chlorido‐bis[(η2‐2‐allyl‐4‐methoxy‐5‐{[(propan‐2‐yloxy)carbonyl]methoxy}phenyl‐κC1)platinum(II)]

Crystallization experiments with the dinuclear chelate ring complex di‐μ‐chlorido‐bis[(η²‐2‐allyl‐4‐methoxy‐5‐{[(propan‐2‐yloxy)carbonyl]methoxy}phenyl‐κC¹)platinum(II)], [Pt₂(C₁₅H₁₉O₄)₂Cl₂], containing a derivative of the natural compound eugenol as ligand, have been performed. Using five different sets of crystallization conditions resulted in four different complexes which can be further used as starting compounds for the synthesis of Pt complexes with promising anticancer activities. In the case of vapour diffusion with the binary chloroform–diethyl ether or methylene chloride–diethyl ether systems, no change of the molecular structure was observed. Using evaporation from acetonitrile (at room temperature), dimethylformamide (DMF, at 313 K) or dimethyl sulfoxide (DMSO, at 313 K), however, resulted in the displacement of a chloride ligand by the solvent, giving, respectively, the mononuclear complexes (acetonitrile‐κN)(η²‐2‐allyl‐4‐methoxy‐5‐{[(propan‐2‐yloxy)carbonyl]methoxy}phenyl‐κC¹)chloridoplatinum(II) monohydrate, [Pt(C₁₅H₁₉O₄)Cl(CH₃CN)]·H₂O, (η²‐2‐allyl‐4‐methoxy‐5‐{[(propan‐2‐yloxy)carbonyl]methoxy}phenyl‐κC¹)chlorido(dimethylformamide‐κO)platinum(II), [Pt(C₁₅H₁₉O₄)Cl(C₂H₇NO)], and (η²‐2‐allyl‐4‐methoxy‐5‐{[(propan‐2‐yloxy)carbonyl]methoxy}phenyl‐κC¹)chlorido(dimethyl sulfoxide‐κS)platinum(II), determined as the analogue {η²‐2‐allyl‐4‐methoxy‐5‐[(ethoxycarbonyl)methoxy]phenyl‐κC¹}chlorido(dimethyl sulfoxide‐κS)platinum(II), [Pt(C₁₄H₁₇O₄)Cl(C₂H₆OS)]. The crystal structures confirm that acetonitrile interacts with the Pt^II atom via its N atom, while for DMSO, the S atom is the coordinating atom. For the replacement, the longest of the two Pt—Cl bonds is cleaved, leading to a cis position of the solvent ligand with respect to the allyl group. The crystal packing of the complexes is characterized by dimer formation via C—H…O and C—H…π interactions, but no π–π interactions are observed despite the presence of the aromatic ring.     

Synthesis,structure and in vitro cytotoxicity testing of some 2‐aroylbenzofuran‐3‐ols

Five 2‐aroyl‐5‐bromobenzo[b]furan‐3‐ol compounds (two of which are new) and four new 2‐aroyl‐5‐iodobenzo[b]furan‐3‐ol compounds were synthesized starting from salicylic acid. The compounds were characterized by mass spectrometry and ¹H NMR and ¹³C NMR spectroscopy. Single‐crystal X‐ray diffraction studies of four compounds, namely, (5‐bromo‐3‐hydroxybenzofuran‐2‐yl)(4‐fluorophenyl)methanone, C₁₅H₈BrFO₃, (5‐bromo‐3‐hydroxybenzofuran‐2‐yl)(4‐chlorophenyl)methanone, C₁₅H₈BrClO₃, (5‐bromo‐3‐hydroxybenzofuran‐2‐yl)(4‐bromophenyl)methanone, C₁₅H₈Br₂O₃, and (4‐bromophenyl)(3‐hydroxy‐5‐iodobenzofuran‐2‐yl)methanone, C₁₅H₈BrIO₃, were also carried out. The compounds were tested for their in vitro cytotoxicity on the four human cancer cell lines KB, Hep‐G2, Lu‐1 and MCF7. Six compounds show good inhibiting abilities on Hep‐G2 cells, with IC₅₀ values of 1.39–8.03 µM.     

The trans influence of the pyridine ligand on ruthenium(II)–porphyrin–carbene complexes

In the two ruthenium(II)–porphyrin–carbene complexes ­(di­benzoyl­carbenyl‐κC)(pyridine‐κN)(5,10,15,20‐tetra‐p‐tolyl­porphyrinato‐κ⁴N)­ruthenium(II), [Ru(C₁₅H₁₀O₂)(C₅H₅N)(C₄₈H₃₆N₄)], (I), and (pyridine‐κN)(5,10,15,20‐tetra‐p‐tolyl­porphyrinato‐κ⁴N)[bis(3‐tri­fluoro­methyl­phenyl)­carbenyl‐κC]­ruthenium(II), [Ru(C₁₅H₈F₆)(C₅H₅N)(C₄₈H₃₆N₄)], (II), the pyridine ligand coordinates to the octahedral Ru atom trans with respect to the carbene ligand. The C(carbene)—Ru—N(pyridine) bonds in (I) coincide with a crystallographic twofold axis. The Ru—C bond lengths of 1.877 (8) and 1.868 (3) Å in (I) and (II), respectively, are slightly longer than those of other ruthenium(II)–porphyrin–carbene complexes, owing to the trans influence of the pyridine ligands.     

Covalent‐assisted supramolecular synthesis: the effect of hydrogen bonding in cocrystals of 4‐tert‐butylbenzoic acid with isoniazid and its derivatized forms

A series of cocrystals of isoniazid and four of its derivatives have been produced with the cocrystal former 4‐tert‐butylbenzoic acid via a one‐pot covalent and supramolecular synthesis, namely 4‐tert‐butylbenzoic acid–isoniazid, C₆H₇N₃O·C₁₁H₁₄O₂, 4‐tert‐butylbenzoic acid–N′‐(propan‐2‐ylidene)isonicotinohydrazide, C₉H₁₁N₃O·C₁₁H₁₄O₂, 4‐tert‐butylbenzoic acid–N′‐(butan‐2‐ylidene)isonicotinohydrazide, C₁₀H₁₃N₃O·C₁₁H₁₄O₂, 4‐tert‐butylbenzoic acid–N′‐(diphenylmethylidene)isonicotinohydrazide, C₁₉H₁₅N₃O·C₁₁H₁₄O₂, and 4‐tert‐butylbenzoic acid–N′‐(4‐hydroxy‐4‐methylpentan‐2‐ylidene)isonicotinohydrazide, C₁₂H₁₇N₃O₂·C₁₁H₁₄O₂. The co‐former falls under the classification of a `generally regarded as safe' compound. The four derivatizing ketones used are propan‐2‐one, butan‐2‐one, benzophenone and 3‐hydroxy‐3‐methylbutan‐2‐one. Hydrogen bonds involving the carboxylic acid occur consistently with the pyridine ring N atom of the isoniazid and all of its derivatives. The remaining hydrogen‐bonding sites on the isoniazid backbone vary based on the steric influences of the derivative group. These are contrasted in each of the molecular systems.     

Different hydrogen‐bonded structures in three 2‐thienyl‐substituted tetrahydro‐1,4‐epoxy‐1‐benzazepines

The molecules of (2RS,4SR)‐2‐exo‐(5‐bromo‐2‐thienyl)‐7‐chloro‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C₁₄H₁₁BrClNOS, (I), are linked into cyclic centrosymmetric dimers by C—H...π(thienyl) hydrogen bonds. Each such dimer makes rather short Br...Br contacts with two other dimers. In (2RS,4SR)‐2‐exo‐(5‐methyl‐2‐thienyl)‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C₁₅H₁₅NOS, (II), a combination of C—H...O and C—H...π(thienyl) hydrogen bonds links the molecules into chains of rings. A more complex chain of rings is formed in (2RS,4SR)‐7‐chloro‐2‐exo‐(5‐methyl‐2‐thienyl)‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C₁₅H₁₄ClNOS, (III), built from a combination of two independent C—H...O hydrogen bonds, one C—H...π(arene) hydrogen bond and one C—H...π(thienyl) hydrogen bond.     

Tunable Fluorophores Based on 2‐(N‐Arylimino)pyrrolyl Chelates of Diphenylboron: Synthesis,Structure, Photophysical Characterization,and Application in OLEDs

Reactions of 2‐(N‐arylimino)pyrroles (HNC₄H₃C(H)?N‐Ar) with triphenylboron (BPh₃) in boiling toluene afford the respective highly emissive N,N′‐boron chelate complexes, [BPh₂{κ²N,N′‐NC₄H₃C(H)?N‐Ar}] (Ar=C₆H₅ ( 12 ), 2,6‐Me₂‐C₆H₃ ( 13 ), 2,6‐iPr₂‐C₆H₃ ( 14 ), 4‐OMe‐C₆H₄ ( 15 ), 3,4‐Me₂‐C₆H₃ ( 16 ), 4‐F‐C₆H₄ ( 17 ), 4‐NO₂‐C₆H₄ ( 18 ), 4‐CN‐C₆H₄ ( 19 ), 3,4,5‐F₃‐C₆H₂ ( 20 ), and C₆F₅ ( 21 )) in moderate to high yields. The photophysical properties of these new boron complexes largely depend on the substituents present on the aryl rings of their N‐arylimino moieties. The complexes bearing electron‐withdrawing aniline substituents 17 – 20 show more intense (e.g., ?_f=0.71 for Ar=4‐CN‐C₆H₄ ( 19 ) in THF), higher‐energy (blue) fluorescent emission compared to those bearing electron‐donating substituents, for which the emission is redshifted at the expense of lower quantum yields (?_f=0.13 and 0.14 for Ar=4‐OMe‐C₆H₄ ( 15 ) and 3,4‐Me₂‐C₆H₃ ( 16 ), respectively, in THF). The presence of substituents bulkier than a hydrogen atom at the 2,6‐positions of the aryl groups strongly restricts rotation of this moiety towards coplanarity with the iminopyrrolyl ligand framework, inducing a shift in the emission to the violet region (λ_max=410–465 nm) and a significant decrease in quantum yield (?_f=0.005, 0.023, and 0.20 for Ar=2,6‐Me₂‐C₆H₃ ( 13 ), 2,6‐iPr₂‐C₆H₃ ( 14 ), and C₆F₅ ( 21 ), respectively, in THF), even when electron‐withdrawing groups are also present. Density functional theory (DFT) and time‐dependent DFT (TD‐DFT) calculations have indicated that the excited singlet state has a planar aryliminopyrrolyl ligand, except when prevented by steric hindrance (ortho substituents). Calculated absorption maxima reproduce the experimental values, but the error is higher for the emission wavelengths. Organic light‐emitting diodes (OLEDs) have been fabricated with the new boron complexes, with luminances of the order of 3000 cd m^?2 being achieved for a green‐emitting device.