Margarita S. Avdontceva

Diiodomethane as a halogen bond donor toward metal-bound halides

A 1,3,5,7,9-pentaazanona-1,3,6,8-tetraenate (PANT) chloride platinum(II) complex (1) was obtained via the metal-mediated double coupling of 2,3-diphenylmaleimidine with both nitrile ligands in trans-[PtCl2(NCtBu)2]. Compound 1 was then co-crystallized with diiodomethane forming solvate 1·½CH2I2. The XRD experiment reveals that this solvate displays the halogen bonds H2C(I)–I⋯Cl–Pt and hydrogen bonds I2C(H)–H⋯Cl–Pt, which join two complex and one CH2I2 molecules in a heterotrimeric supramolecular cluster. Inspection of the CCDC database reveals only one example of the halogen bond H2C(I)–I⋯I–Pt between the CH2I2 molecule and metal-coordinated halide in the structure of VEMWOA. In VEMWOA, CH2I2 serves solely as a halogen bond donor with no hydrogen bond contribution. Results of the Hirshfeld surface analysis and DFT calculations (M06/DZP-DKH level of theory) followed by topological analysis of the electron density distribution within the formalism of Baders theory (QTAIM method) for both 1·½CH2I2 and VEMWOA confirmed the formation of these weak interactions. The evaluated energies of halogen bonds involving CH2I2 are in the 2.2–2.8 kcal mol−1 range.

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

Summary 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.

Zinc(II)-mediated generation of 5-amino substituted 2,3-dihydro-1,2,4-oxadiazoles and their further ZnII-catalyzed and O2-involving transformations

ZnII-activated cyanamides NCNR2 (R2 = Me2, Et2, C5H10, (CH2)2O(CH2)2, Ph2) react with the acyclic N-alkyl ketonitrones Ph2CN+(O−)R′ (R′ = Me, CH2Ph) and N-aryl ketonitrones (R′ = Ph, p-BrC6H4, p-EtC6H4) under mild conditions. Uncomplexed 5-aminosubstituted 2,3-dihydro-1,2,4-oxadiazoles (6 examples; 49–82%) were obtained in zinc(II)-involving cycloaddition of the N-alkyl ketonitrones to the cyanamide substrates; these 2,3-dihydro-1,2,4-oxadiazoles undergo ring-opening giving carbamoylamidines and methylidenureas. The N-aryl ketonitrones react with ZnII-activated cyanamides giving the open-chain systems, viz. carbamoylamidines, N′-(2-(diphenylmethylidene)amino)-phenyl-N,N-carbamimidic acids, and methylidenureas, which are presumably formed via the cycloaddition route followed by the N–O cleavage induced by the acceptor character of the aryl groups.

Alkylation and Aminomethylation of 1,3-Dihydro-2Н-Benzimidazole-2-Thione

Alkylation of 1,3-dihydro-2Н-benzimidazole-2-thione (2-mercaptobenzimidazole) with bromoethane and chloroacetic acid derivatives occurrs at the sulfur atom, leading to the corresponding 2-sulfanylbenz-imidazole derivatives. Aminomethylation of 1,3-dihydro-2Н-benzimidazole-2-thione with piperidine and 4-methylpiperidine gives reaction products at both nitrogen atoms, while reaction with morpholine gives derivative at only one nitrogen atom, which is in an equilibrium with the starting compound and bis-adduct in DMSO solution.

Brominated CF3-allyl alcohols as multicentered electrophiles in TfOH promoted reactions with arenes

Superacidic activation of CF3-substituted allyl alcohols, bearing one or two bromine atoms at the CC double bond, with TfOH was studied. These brominated alcohols were found to behave as highly reactive multicentered electrophiles. The obtained cationic intermediates were studied by means of NMR and DFT calculations. The protonation of dibromo derivatives with TfOH resulted in cyclization to form trifluoromethylated 1H-indenes and/or indan-1-ones in yields up to 90%. The reaction of dibromosubstituted CF3-allyl alcohols with arenes in the presence of TfOH gave rise to either CF3-alkenes (formal substitution of hydroxyl with an aryl group) or CF3-indenes, depending on the nucleophilicity and bulkiness of the starting arenes. The reaction of monobrominated CF3-substituted allyl alcohols with arenes in TfOH afforded two regioisomeric CF3-alkenes, as a result of arylation of both terminal carbons of the allyl system, in yields up to 95%. The obtained brominated CF3-alkenes can be converted efficiently into trifluoromethylated allenes by treatment with KOH in ethanol in yields up to 92%.

Halogen and hydrogen bonding in cis-dichlorobis(propionitrile)platinum(II) chloroform monosolvate

Abstract The weak intermolecular noncovalent interactions in the solvate cis-[PtCl2(C2H5CN)2]·CHCl3 were studied by XRD and DFT methods. Special attention was paid to a chloroform molecule as a potential donor of both hydrogen and halogen bonds. On the one hand, the H atom of chloroform links two Cl atoms of cis-[PtCl2(C2H5CN)2] (Hchloroform–Clcomplex (2.660 Å, 2.811 Å)), and on the other side, the weak Clchloroform–Clcomplex (3.247 and 3.497 Å) interactions were found. According to DFT calculation, only the Hchloroform–Clcomplex (2.660 and 2.811 Å) and Clchloroform–Clcomplex (3.247 Å) interactions can be classified as weak noncovalent bonds, whereas the contacts Clchloroform–Cnitrile (3.391 Å) and Clchloroform–Clcomplex (3.497 Å) are due to the crystal packing effect.

Synthesis of thiazolidines via regioselective addition of unsymmetric thioureas to maleic acid derivatives

A wide range of unsymmetric thioureas has been studied in reaction with N-arylmaleimides and maleic anhydride. The regioselectivity of the addition depends not only on steric factors but on both solvent polarity and type of maleic acid derivative (imide or anhydride). The general regularities have been established providing practical guidelines to control the reaction result. The unequivocal structural assignment of all products has been done using NMR spectroscopy including 15N–1H HMBC experiments.

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 cis-[PdCl2(CNXyl)2] (Xyl = 2,6-Me2C6H3) with the aminoazoles [1 H-imidazol-2-amine (1), 4 H-1,2,4-triazol-3-amine (2), 1 H-tetrazol-5-amine (3), 1 H-benzimidazol-2-amine (4), 1-alkyl-1 H-benzimidazol-2-amines, where alkyl = Me (5), Et (6)] 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-C(N-azolyl)N(Xyl)C═NXyl}] (7-12; 73-91%). Compounds 7-12 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-holeisocyanide···πarene 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 7-9 followed by the topological analysis of the electron density distribution within the framework of Baders 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 7-9 revealed that π(C-C)Xyl → π*(C-N)isocyanide charge transfer (CT) takes place along with the intramolecular π-holeisocyanide···πarene 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 p-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-holeisocyanide···πarene interaction effect on the stabilization of the in-conformation in metal-bound acyclic diaminocarbenes.

Synthesis and crystal structure of 2‐isocyano‐4‐methylphenyl diphenylacetate: a rare case of an easily accessible odourless isocyanide

Acidic hydrogen containing 2-isocyano-4-methylphenyl diphenylacetate, C22H17NO2, (I), was synthesized by the base-promoted reaction between 5-methylbenzoxazole and diphenylacetyl chloride. Achiral (I) crystallizes in the chiral P212121 space group. The C[triple-bond]N bond length is 1.164 (2) Å and the angle between the OCO and 2-isocyano-4-methylphenyl planes is 69.10 (16)°. Molecules are linked via C=O...H(phenyl) and bifurcated N[triple-bond]C...H(phenyl)/N[triple-bond]C...H(methine) hydrogen bonds, forming one-dimensional arrays.

Tetrachloromethane as halogen bond donor toward metal-bound halides

Abstract Two annulated triazapentadiene systems, viz. 1,3,5,7,9-pentaazanona-1,3,6,8-tetraenate chloride complexes of PtII, form CCl4 solvates, containing the Cl3C–Cl···Cl–Pt halogen bonds. These halogen bonds are firstly reported type of Cl3C–Cl···Cl–M contacts. In the X-ray structures of two solvates different non-covalent interactions were detected and studied by DFT calculations and topological analysis of the electron density distribution within the framework of QTAIM method at the M06/DZP-DKH level of theory. Estimated energies of these supramolecular contacts vary from 0.6 to 2.4 kcal/mol.