Ashok K.S. Chauhan

Synthesis and characterization of monomeric diorganotellurium dihalides: crystal and molecular structures of diphenacyltellurium dibromide and -diiodide

Abstract Tellurium, but not selenium, reacts with phenacyl bromide (ω-bromoacetophenone) to give diphenacyltellurium dibromide (PhCOCH2)2TeBr2 (1), which represents the first example of a functionally substituted organotellurium halide to have been prepared directly from elemental tellurium and an organic halide. Metathesis of 1 with KI affords the crystalline diiodide, (PhCOCH2)2TeI2 (2), but halide–pseudohalide exchange does not proceed with KSCN or AgN3. Compounds 1 and 2 have been characterized by elemental analyses, IR, 1H- and 13C-NMR and mass spectrometry. Coordinative interaction of both the carbonyl groups in 1 and 2, in solid state as well as in solution, is indicated by IR spectra. Crystal and molecular structures of the dihalides were determined by X-ray diffraction method. Compounds 1 and 2 are isostructural and crystallize in the monoclinic system with space group P21/n. The primary geometry about the central Te atom in both the compounds is Ψ-trigonal-bipyramidal with axial halogens. Stereochemically active lone pair of electrons occupies the equatorial plane along with methylene C atoms of the organic ligands. The Te⋯O intramolecular attractive interactions, though weak [Te⋯O(1), Te⋯O(2): 2.938, 2.912 A in 1 and 2.877, 2.818 A in 2] appear to saturate tellurium(IV) atom coordinatively so as to prevent intermolecular Te⋯Br/I interactions. However, there is evidence of weak intermolecular TeBr⋯H(methylene) secondary interactions in compound 1, leading to the formation of supramolecular assemblies.

Acylmethyl(aryl)tellurium(IV,II) derivatives: intramolecular secondary bonding and steric rigidity

Electrophilic substitution of acylmethanes (methyl ketones), RCOCH3 (R = i-Pr, 1; Et, 2; Me, 3) with aryltellurium trichlorides, ArTeCl3 (Ar = 1-C10H7, Np, A; 2,4,6-Me3C6H2, Mes, B; 4-MeOC6H4, Anisyl, C) under mild conditions affords the corresponding acylmethyl(aryl)tellurium dichlorides (RCOCH2)ArTeCl2. Reduction of the dichlorides, gives tellurides, (i-PrCOCH2)ArTe, 1A-1C, which give the corresponding dihalides, (i-PrCOCH2)ArTeX2 (X = Cl, 1Aa-1Ca; Br, 1Ab-1Cb; I, 1Ac-1Cc) when reacted in situ with SO2Cl2, Br2 or I2. The unsymmetric tellurides are labile towards disproportionation and attempts to obtain them lead to the isolation of Ar2Te2 except in the case of (i-PrCOCH2)MesTe (1B), which represents an interesting example of a kinetically stable aryl(alkyl)telluride. All the dihalomesityltellurium(IV) derivatives show separate 1H and 13C NMR signals for the ortho methyls irrespective of the sizes of R and X ligands. The telluride, 1B with free rotation about Te-C(mesityl) bond shows, like the unsymmetric diorganotellurium(IV) dihalides, only one 125Te NMR signal. The 1,4-chelating behavior of the acyl ligand among diorganotellurium(IV) compounds is inferred from the X-ray diffraction data for 1Aa, 1Ac, 1Ba, 1Bb, 1cA and 1Cc which are indicative of the presence of intramolecular Te...O secondary bonding interactions (SBIs) at least in the solid state. As a consequence, steric repulsion in case of the mesityltellurium(IV) derivatives, 1Ba and 1Bb, reaches the threshold so as to cause loss of two-fold rotational symmetry of the mesityl group about the Te-C(mesityl) bond axis. Intermolecular C-HO...O H-bonding interactions appears to stabilize such an orientation of the aryl ligand at least in the solid state.

Transition metal schiff base chelates as ligands for phenyltin(IV) chlorides

SummaryBinuclear complexes of phenyltin(IV) chlorides with transition metal chelates of tetradentate Schiff bases derived from acetylacetone, benzoylacetone oro-hydroxyacetophenone and ethylenediamine or propylenediamine, of the general formula PhnSnCl4-nML (where n = 1 or 2, M = Ni11 or Cu11 and L2−= the Schiff base dianion), have been synthesised and characterized through elemental analysis, conductance and i.r. spectroscopic data. The coordination of metal chelates to tin involves two triply bonded oxygen atoms giving rise to an octahedral environment around SnIV. The molar conductance of the complexes in nitrobenzene shows the presence of the uncoordinated ML and phenyltin(IV) chloride moieties in solution.

Trioganotin (IV) Complexes of Schiff Bases Derived from S-methyl and -Benzyldithiocarbazate

Abstract Five and six coordinate complexes of triorganotin (IV) moieties with Schiff bases derived from S-methyl or -benzyldithiocarbazate and a ketone or pyridine-2-carboxaldehyde, respectively, have been synthesised and characterized by elemental analysis, molar conductance, molecular weight determination and ultraviolet and infrared spectroscopy. The complexes are nonelectrolytic and monomeric in solution.

Organotellurium(IV) Chelates of Tri-and Tetradentate Schiff Bases

Abstract Several new organotellurium(IV) chelates of the Schiff bases having the formula, R2TeL (R=phenyl, p-methoxyphenyl, p-ethoxyphenyl) or R2Te= (L2-=dianions of planar tetradentate ligands with the ONNO donor system or tridentate ligands with the ONO and SNO donor systems) have been prepared. Their structures have been examined in the solid state and in solution through spectral studies.

Controlled hydrolysis of aryltellurium trichlorides using 2-pyrrolidinones: isolation and structural characterization of monomeric aryltellurium(IV) monohydroxides

The 2-pyrrolidinone (Pyrr)-assisted hydrolysis of aryltellurium trichlorides, provided their first-step hydrolysis products as 1 : 1 molecular adducts, ArTeCl2OH.Pyrr (Ar = 1-C10H7, Npl, 1; 2,4,6-Me3C6H2, Mes, 2). The hydroxo ligand occupies an equatorial position in the ψ-trigonal bipyramidal geometry around Te(IV) and is involved in a strong H-bonding interaction with the amido O of the base. As NplTeBr3 did not react with 2-pyrrolidinone under similar conditions, the bromo analogue of 1, NplTeBr2OH.Pyrr (3), was prepared by a metathetical reaction with NaBr. Both 1 and 2 undergo electrophilic substitution with acetone and pinacolone to afford Ar(RCOCH2)TeCl2 (R = Me, t-Bu), but do not react with iodoacetic acid, suggesting that the hydroxo ligand acts as a nucleophile rather than a base. The Te–OH bond in 1 is also cleaved by CH3COCl to give the parent trihalide NplTeCl3, while reaction with BrCH2COBr results in NplTeBr3 (4) as the ultimate tellurium containing product. The reaction of NplTeCl3 with N-Methyl protected 2-pyrrolidinone (PyrrMe), under similar conditions, gave an ionic complex [(PyrrMe)2H] [NplTeCl4] (5), but did not react with N-acyl protected 2-pyrrolidinone, PyrrCOCH2Br. However, the latter added oxidatively to elemental tellurium to give (PyrrCOCH2)2TeBr2 (6). In the crystal lattice of 5, discreet five-coordinate square pyramidal CTeX4 units are present, while in the case of 4 the same units are realized via intermolecular Te⋯Br interactions in a one-dimensional supramolecular architecture. N-(2-pyrrolidinone)amidomethyl ligands in 6 adopt a rare, if not the first, 1,6-(C,O) mode of chelation in preference to 1,4-(C,O) mode often observed in similar Te(IV) compounds.

Hydrotelluration of acetylenic esters: structural characterization of stereoisomers of methyl/ethyl β-(aryltelluro)acrylates

Synthesis and complete characterization of some ester functionalized vinylic tellurides bearing an aryl ligand with varying steric and electronic effects bound to tellurium is described. Hydrotelluration of methyl propiolate using Ar2Te2/NaBH4 in methanol results in a mixture of stereoisomers of methyl β-(aryltelluro)acrylates, ArTeCHCHCOOMe (Ar = 4-MeOC6H4, 1A; 1-C10H7, 2A; 2,4,6-Me3C6H2, 3A; C5H5FeC5H4, 4A; 4-Me2NC6H4, 5A; and 2-C4H3S, 6A). The same reaction in ethanol provides isomeric mixtures of the ethyl esters ArTeCHCHCOOEt (1B–6B). However, in the reactions between methyl propiolate and Ar2Te2 (Ar = 2,4,6-Me3C6H2, 4-Me2NC6H4) in isopropanol or t-butanol, no exchange of alkyl groups between the parent ester and the solvent is observed, instead detelluration of the Ar2Te2 to Ar2Te is a competing reaction along with almost exclusive formation of the (Z)-isomers (3Aa, 5Aa). The geometry of the separated stereoisomers is established in solution, with the help of 1H, 13C and 125Te NMR spectrometry. Of particular interest is the observation that 125Te chemical shifts {deshielded in (Z) compared to (E); Δδ = 106–136 ppm} and the geminal heteronuclear coupling constants {2J(1H–125Te) values for (E) are more than seven times that of the corresponding (Z) isomer} can be used to distinguish between liquid isomers. Structural characterization in the solid state by single-crystal X-ray diffraction for the 2Ba, 3Aa, 3Ba, 5Aa, 8 (Z)-isomers as well as for both stereoisomers of 4-Me2NC6H4TeCHCHCOOEt (5Ba and 5Bb) is also presented. The carbonyl O atom of the ester group is invariably involved, at least in the solid state, in a secondary bonding interaction with the Te(II) atom. While an intermolecular Te⋯O interaction gives rise to one-dimensional supramolecular arrays in the crystal lattice of 5Bb with (E) configuration, it is realized intramolecularly in the case of the (Z)-isomers due to the cis position of the chalcogen atoms.

Functionalized Organotellurium Halides: Synthesis, Characterization, and Observation of Intra- and Intermolecular Secondary Bonding

Abstract Activated tellurium, but not selenium, reacts with para-substituted benzoylmethyl bromides as well as with iodoacetamide at their melting points in absence of a solvent to give bis(p-substituted benzoylmethyl)tellurium dibromides, (p-YC6H4COCH2)2TeBr2, (Y = H, Me, and MeO) and bis(acetamido)tellurium diiodide, (H2NCOCH2)2TeI2, respectively. Quick reduction of (p-YC6H4COCH2)2TeBr2, with sodium metabisulphite in a two-phase system yields crystalline (p-YC6H4COCH2)2Te. These tellurides undergo smooth oxidative addition of halogens, interhalogen ICl or a pseudohalogen (SCN)2. Intramolecular coordination of the carbonyl group in these functionalized diorganotellurium dihalides is evident from IR spectra and shorter Te···O (carbonyl) distances in comparison to the sum of van der Waals radii and completes six coordination around Te atom. Not unexpectedly, therefore, intermolecular secondary bonding effects of the type Te…O, Te···X and X···X are missing in (PhCOCH2)2TeBr2, (p-MeOC6H4COCH2)TeBr2 and (PhCOCH2)2TeI2. Instead, these compounds provide rare examples, among organotellurium compounds, of supramolecular architecture, where C–H···Br and C–H···O hydrogen bonds and π-π (phenyl ring) interactions appear to be the noncovalent intermolecular associative forces that dominate the crystal packing.

Phenylmercury(II) Haloacetates and their Complexes with Group VB Donors

Abstract Haloacetic acids cleave one of the two Ph-Hg bonds of diphenylmercury under mild conditions providing thereby a direct synthetic route to a number of phenylmercury(I1) haloacetates, PhHgOOCR (R = CH2I, CH2Br, CH2C1, CC13 or CF3) in nearly quantitative yield. Interaction of these arylmercuric haloacetates with ligands having atoms of Group VB elements (N, P, As or Sb) as donors, gives rise to molecular adducts of 1:l or 2 : l (in case of diphos) stoichiometry which are monomeric and non-electrolytesin nitrobenzene.

Adducts of tellurium and organotellurium(IV) chlorides with transition metal chelates of tetradentate schiff bases

SummaryCoordinative interaction between tellurium tetrachloride or aryltellurium trichloride and transition metal chelates of tetradentate Schiff bases has yielded bimetallic molecular adducts of the general formula RnTeCl4−n · ML [n = 0 or 1, R = Ph,p-MeOC6H4 orp-EtOC6H4, M = nickel(II) or copper(II) and L2− dianion of the Schiff bases derived from salicylaldehyde oro-hydroxyacetophenone and ethylenediamine]. The i.r. spectral and magnetic measurements on the complexes in the solid state indicate coordination of the metal chelates to tellurium(IV)via two phenolic oxygens. Planarity about the transition metal ion is thus retained.