Structures and photophysical properties of 3,4-diaryl-1H-pyrrol-2,5-diimines and 2,3-diarylmaleimides

Structural features of 3,4-diaryl-1H-pyrrol-2,5-diimines and their derivatives have been studied by molecular spectroscopy techniques, single-crystal X-ray diffraction, and DFT calculations. According to the theoretical calculations, the diimino tautomeric form of 3,4-diaryl-1H-pyrrol-2,5-diimines is more stable in solution than the imino-enamino form. We also found that the structurally related 2,3 exist in the solid state in the dimeric diketo form. 3,4-Diary1-1H-pyrrol-2,5-diimines and 2,3-diarylmaleimides exhibit fluorescence in the blue region of the visible spectrum. The fluorescence spectra have large Stokes shifts. Aryl substituents at the 3,4-positions of 1H-pyrrol-2,5-diimine do not significantly affect fluorescence properties. The insertion of donor substituents into 2,3diarylmaleimides leads to bathochromic shift of emission bands with hyperchromic effect. (C) 2017 Elsevier B.V. All rights reserved

Isoxazolium N-ylides and 1-oxa-5-azahexa-1,3,5-trienes on the way from isoxazoles to 2H-1,3-oxazines

Theoretical and experimental studies of the reaction of isoxazoles with diazo compounds show that the formation of 2H-1,3-oxazines proceeds via the formation of (3Z)-1-oxa-5-azahexa-1,3,5-trienes which undergo a 6π-cyclization. The stationary points corresponding to the probable reaction intermediates, isoxazolium N-ylides, were located by DFT calculations at the B3LYP/6-31G(d) level only for derivatives without a substituent in position 3 of the isoxazole ring. These isoxazolium N-ylides are thermodynamically and kinetically very unstable. According to the calculations and experimental results 2H-1,3-oxazines are usually more thermodynamically stable than the corresponding open-chain isomers, (3Z)-1-oxa-5-azahexa-1,3,5-trienes. The exception are oxaazahexatrienes derived from 5-alkoxyisoxazoles, which are thermodynamically more stable than the corresponding 2H-1,3-oxazines. Therefore, the reaction of diazo esters with 5-alkoxyisoxazoles is a good approach to 1,4-di(alkoxycarbonyl)-2-azabuta-1,3-dienes. The reaction conditions for the preparation of aryl- and halogen-substituted 2H-1,3-oxazines and 1,4-di(alkoxycarbonyl)-2-azabuta-1,3-dienes from isoxazoles were investigated

Bifunctional Reactivity of Amidoximes Observed upon Nucleophilic Addition to Metal-Activated Nitriles

Treatment of the aromatic nitrile complexes <i>trans</i>-[PtCl₂(RC₆H₄CN)₂] (R = <i>p</i>-CF₃ <b>NC1</b>, H <b>NC2</b>, <i>o</i>-Cl <b>NC3</b>) with the aryl amidoximes <i>p</i>-R′C₆H₄C­(NH₂)NOH (R′ = Me <b>AO1</b>, H <b>AO2</b>, Br <b>AO3</b>, CF₃ <b>AO4</b>, NO₂ <b>AO5</b>) in all combinations, followed by addition of 1 equiv of AgOTf and then 5 equiv of Et₃N, leads to the chelates [PtCl­{H<u>N</u>C­(RC₆H₄)­O<u>N</u>C­(C₆H₄R′-<i>p</i>)­NC­(RC₆H₄)<u>N</u>H}] (<b>1</b>–<b>15</b>; 15 examples; yields 71–88% after column chromatography) derived from the platinum­(II)-mediated coupling between metal-activated nitriles and amidoximes. The mechanism of this reaction was studied experimentally by trapping and identification of the reaction intermediates, and it was also investigated theoretically at the DFT level of theory. The combined experimental and theoretical results indicate that the coupling with the nitrile ligands involves both the HON and monodeprotonated NH₂ groups of the amidoximes, whereas in the absence of the base, the NH₂ functionality is inactive toward the coupling. The observed reaction represents the first example of bifunctional nucleophilic behavior of amidoximes. The complexes <b>1</b>–<b>16</b> were characterized by elemental analyses (C, H, N), high-resolution ESI⁺-MS, FTIR, and ¹H NMR techniques, whereas unstable <b>17</b> was characterized by HRESI⁺-MS and FTIR. In addition, <b>8</b>·C₄H₈O₂, <b>12</b>, and <b>16</b>·CHCl₃ were studied by single-crystal X-ray diffraction

Ligation-Enhanced π‑Hole···π Interactions Involving Isocyanides: Effect of π‑Hole···π Noncovalent Bonding on Conformational Stabilization of Acyclic Diaminocarbene Ligands

The reaction of <i>cis</i>-[PdCl₂­(CNXyl)₂] (Xyl = 2,6-Me₂C₆H₃) with the aminoazoles [1<i>H</i>-imidazol-2-amine (<b>1</b>), 4<i>H</i>-1,2,4-triazol-3-amine (<b>2</b>), 1<i>H</i>-tetrazol-5-amine (<b>3</b>), 1<i>H</i>-benzimidazol-2-amine (<b>4</b>), 1-alkyl-1<i>H</i>-benzimidazol-2-amines, where alkyl = Me (<b>5</b>), Et (<b>6</b>)] in a 2:1 ratio in the presence of a base in CHCl₃ at RT proceeds regioselectively and leads to the binuclear diaminocarbene complexes [(ClPdCNXyl)₂­{μ-<u>C</u>­(<u>N</u>-azolyl)­N­(Xyl)<u>C</u>NXyl}] (<b>7</b>–<b>12</b>; 73–91%). Compounds <b>7</b>–<b>12</b> were characterized by C, H, N elemental analyses, high-resolution ESI⁺-MS, Fourier transform infrared spectroscopy, 1D (¹H, ¹³C) and 2D (¹H,¹H-COSY, ¹H,¹H-NOESY, ¹H,¹³C-HSQC, ¹H,¹³C-HMBC) NMR spectroscopies, and X-ray diffraction (XRDn). Inspection of the XRDn data and results of the Hirshfeld surface analysis suggest the presence in all six structures of intramolecular π-hole_isocyanide···π_arene interactions between the electrophilic C atom of the isocyanide moiety and the neighboring arene ring. These interactions also result in distortion of the Pd–CN–Xyl fragment from the linearity. Results of density functional theory calculations [M06/MWB28 (Pd) and 6-31G* (other atoms) level of theory] for model structures of <b>7</b>–<b>9</b> followed by the topological analysis of the electron density distribution within the framework of Bader’s theory (QTAIM method) reveal the presence of these weak interactions also in a CHCl₃ solution, and their calculated strength is 1.9–2.2 kcal/mol. The natural bond orbital analysis of <b>7</b>–<b>9</b> revealed that π­(C–C)­Xyl → π*­(C–N)­isocyanide charge transfer (CT) takes place along with the intramolecular π-hole_isocyanide···π_arene interactions. The observed π­(C–C)_Xyl → π*­(C–N)_isocyanide CT is due to ligation of the isocyanide to the metal center, whereas in the cases of the uncomplexed <i>p</i>-CNC₆H₄NC and CNXyl species, the effects of CT are negligible. Available CCDC data were processed from the perspective of isocyanide-involving π-hole···π interactions, disclosed the role of metal coordination in the π-hole donor ability of isocyanides, and verified the π-hole_isocyanide···π_arene interaction effect on the stabilization of the <i>in</i>-conformation in metal-bound acyclic diaminocarbenes

Reactions of CF3-enones with arenes under superelectrophilic activation: a pathway to trans-1,3-diaryl-1-CF3-indanes, new cannabinoid receptor ligands

4-Aryl-1,1,1-trifluorobut-3-en-2-ones ArCH[double bond, length as m-dash]CHCOCF3 (CF3-enones) react with arenes in excess of Brønsted superacids (TfOH, FSO3H) to give, stereoselectively, trans-1,3-diaryl-1-trifluoromethyl indanes in 35-85% yields. The reaction intermediates, the O-protonated ArCH[double bond, length as m-dash]CHC(OH(+))CF3 and the O,C-diprotonated ArHC(+)CH2C(OH(+))CF3 species, have been studied by means of (1)H, (13)C, (19)F NMR, and DFT calculations. Both types of the cations may participate in the reaction, depending on their electrophilicity and electron-donating properties of the arenes. The formation of CF3-indanes is a result of cascade reaction of protonated CF3-enones to form chemo-, regio- and stereoselectively three new C-C bonds. The obtained trans-1,3-diaryl-1-trifluoromethyl indanes were investigated as potential ligands for cannabinoid receptors CB1 and CB2 types. The most potent compound showed sub-micromolar affinity for both receptor subtypes with a 6-fold selectivity toward the CB2 receptor with no appreciable cytotoxicity toward SHSY5Y cells

CCDC 1518211: Experimental Crystal Structure Determination

Related Article: Anastasiia M. Afanasenko, Dina V. Boyarskaya, Irina A. Boyarskaya, Tatiana G. Chulkova, Yakov M. Grigoriev, Ilya E. Kolesnikov, Margarita S. Avdontceva, Taras L. Panikorovskii, Andrej I. Panin, Anatoly N. Vereshchagin, Michail N. Elinson|2017|J.Mol.Struct.|1146|554|doi:10.1016/j.molstruc.2017.06.048,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

CCDC 1518210: Experimental Crystal Structure Determination

Related Article: Anastasiia M. Afanasenko, Dina V. Boyarskaya, Irina A. Boyarskaya, Tatiana G. Chulkova, Yakov M. Grigoriev, Ilya E. Kolesnikov, Margarita S. Avdontceva, Taras L. Panikorovskii, Andrej I. Panin, Anatoly N. Vereshchagin, Michail N. Elinson|2017|J.Mol.Struct.|1146|554|doi:10.1016/j.molstruc.2017.06.048,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

CCDC 1518077: Experimental Crystal Structure Determination

Related Article: Anastasiia M. Afanasenko, Dina V. Boyarskaya, Irina A. Boyarskaya, Tatiana G. Chulkova, Yakov M. Grigoriev, Ilya E. Kolesnikov, Margarita S. Avdontceva, Taras L. Panikorovskii, Andrej I. Panin, Anatoly N. Vereshchagin, Michail N. Elinson|2017|J.Mol.Struct.|1146|554|doi:10.1016/j.molstruc.2017.06.048,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.