Showing papers by "Andrei V. Churakov published in 1999"

Synthesis, structure, and ion selective complexation of trans and cis isomers of photochromic dithia-18-crown-6 ethers

Abstract: Photochromic styryl dyes containing benzodithia-18-crown-6 and N-substituted benzothiazolium moieties are synthesized and characterized spectroscopically and, for a specific case, by X-ray crystallography. The effects of the N-substituent and of sulfur atom substitution in the crown ether cavity on metal cation complex formation and on photochromism due to reversible trans−cis photoisomerization are evaluated. High selectivities for heavy metal ions, such as Ag+ and Hg2+, are observed, in contrast to the benzo-18-crown-6 dyes which selectively bind alkali and alkali earth cations. Relative complex formation stability constants, determined spectrophotometrically, are converted to absolute values by polarographic measurements. The stability constant for Hg2+ complex formation by the trans dye is enhanced 47-fold upon substitution of the 4-butylsulfonate group for methyl at the nitrogen of the benzothiazolium moiety. Photoisomerization to the cis dye is accompanied by a further 11-fold stability constant inc...

Transition metal dicarbollide complexes: synthesis, molecular, crystal and electronic structures of [M(C2B9H11)(NMe2)3] (M = Nb or Ta) and their insertion reactions with CO2 and CS2†

Abstract: The homoleptic amides [M(NMe2)5] (M = Nb 1 or Ta 2; the latter is characterised by a structural study) reacted with the carborane nido-C2B9H13 to eliminate two equivalents of HNMe2 and generate the dicarbollide half-sandwich tris(dimethylamide) complexes [M(C2B9H11)(NMe2)3] (M = Nb 3 or Ta 4). The crystal structures of isomorphous 3 and 4 have been determined and reveal two NMe2 ligands in a vertical orientation and the third one in a horizontal orientation with respect to the η5-co-ordinated face of the C2B9H11 ligand. The electronic factors responsible for the amide ligand orientations in these complexes are explored using qualitative MO arguments. Complexes 3 and 4 reacted with CO2 and CS2 to yield the tris(carbamate) [M(C2B9H11)(O2CNMe2)3] (M = Nb 5 or Ta 7) and tris(dithiocarbamate) [M(C2B9H11)(S2CNMe2)3] (M = Nb 6 or Ta 8) complexes, respectively. The crystal structures of 6 and 7 show two (dithio)carbamate ligands in horizontal and one in vertical orientation, demonstrating the similarity between the σ,π-donor frontier orbitals of the ligands NMe2 and X2CNMe2 in 4 and 6 or 7 respectively.

A Novel Route to the 5‐[2‐(Diphenylphosphanyl)ethyl]‐1,2,3,4‐tetramethylcyclopentadienyl Ligand – Synthesis and Crystal Structure of [η5:η1‐C5(CH3)4CH2CH2PPh2]ZrCl3·THF

Abstract: The five-step synthesis of the first transition metal complex with the C5(CH3)4CH2CH2PPh2 ligand [η5:η1-C5(CH3)4CH2CH2PPh2]ZrCl3·THF (11), starting from the known compound [2-(dimethylamino)ethyl]tetramethylcyclopentadiene (4) via 4,5,6,7-tetramethylspiro[2,4]hepta-4,6-diene (7), is reported. Lithium cyclopentadienide LiC5(CH3)4CH2CH2PPh2 (9), silylated cyclopentadiene (CH3)3SiC5(CH3)4CH2CH2PPh2 (10) and cyclopentadiene HC5(CH3)4CH2CH2PPh2 (12) were isolated and characterised as pure substances. The crystal structure of the zirconium complex 11 was established by X-ray diffraction analysis.

Crown-containing butadienyl dyes. 1. synthesis, structure, fluorescence, and complex formation of chromogenic aza-15-crown-5 ethers

Abstract: Crown-containing butadienyl dyes containing various heterocyclic moieties and azacrown ether fragments were synthesized for the first time. The spatial structures and the absorption and fluorescence spectra of crown-containing butadienyl dyes and their complexes with metal cations were examined. The effects of the nature of the heterocyclic and crown ether fragments on fluorescence and generation of dyes and their complexes with metal cations were revealed based on the spectral data.

Reaction of trifluoromethyl-containing enones with thiophenol derivatives

Abstract: The reaction of trifluoromethyl-containing enones with thiophenol derivatives has been studied. Reactions with 4-methylthiophenol proceed with the formation of either ketosulfides or a pyran derivative. Reactions of trifluoromethyl-containing enones with 2-mercaptobenzaldehyde lead to 3-trifluoroacetyl-substituted 2H-thiochromenes.

Dimethylthiophosphoryl hydrazone ligands and their copper complexes: crystal structures and analysis of their solution complexation behaviour by electrospray mass spectrometry

Abstract: Four new thiophosphoryl ligands containing NNPS or CNPS connectivities have been prepared and three of them characterised by single-crystal X-ray diffraction. The complexation of these ligands with salts of CuI, CuII, NiII and ZnII has been studied by electrospray mass spectrometry and uv-visible spectrophotometry in acetonitrile and methanol solution. Evidence for 1∶1 and 2∶1 complexation is presented. Two copper(I) complexes were isolated including a mixed chloride–bromide copper(I) complex in which a dimeric structure is adopted with a 22-membered metallacycle.