Ramesh C. Srivastava

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.

Cleavage of metal-aryl (M = Ge, Sn, Pb) bonds with iodine monochloride and monobromide

Abstract Tetraaryl-germanium, -tin and -lead compounds (aryl(Ar) = phenyl, p -tolyl) were treated with IX (X = Cl, Br) in dry carbon tetrachloride under various conditions. Iodine monochloride cleaved one MAr bond in case of Ge and two bonds in case of Sn and Pb to give triarylgermanium chloride and diaryl-tin and -lead dichlorides respectively. In contrast iodine monobromide reacted only to a small extent (~5%) with Ph 4 Ge in boiling ethylene bromide; with Ar 4 Pb the corresponding dibromides were formed, while Ar 4 Sn gave both mono- and dibromides. The SnAr bond is cleaved in preference to Sn—alkyl bonds in Bu n SnPh 4− n ( n = 2, 3). Reaction of Ph 3 SnCl with IBr or Br 2 produced a mixed halogeno-derivative, Ph 2 SnClBr, and the corresponding phenyl halide.

Thicyanogen cleavage of some symmetrical tetraaryland and hexaaryldi-tin and-lead compounds

Abstract Ar4M and Ar4MMAE3 compounds (Ar=phenyl and P-tolyl, M=Sn, and Pb) were treated with freshyl prepared thiocyanogen (SCN)2 anhydrous carbon tetrachloride under various conditions. Unlike the tertraarylleads, the corresponding tin compounds reacted only to a small extent. the hexaaryldi-metals were quite reactive. The metal-containing reaction products have an iso-Ar3M-NCS structure.

Organotellurium derivatives : IV. Synthesis of some diaryltellurium dihalides and pseudohalides

Iodine monohalides (ICl, IBr), cyanogen halides (CNBr, CNI) and thiocyanogen (SCN)2 add oxidatively to diaryltellurium(II), R2Te (R  Ph, p-Ch3OC6H4) under mild conditions (5°C). The resulting organotellurium(IV) derivatives react metathetically with silver pseudohalides to yield several new diaryltellurium(IV) pseudohalide derivatives.

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.

Acyl derivatives of main group metals: preparation of benzoyl derivatives of some group V and VI metals and metalloids

Abstract 3,5-Dinitrobenzoyl chloride ( 1 ) adds oxidatively to triarylantimony to give the first benzoyl derivatives of antimony, Ar 3 Sb[COC 6 H 3 (NO 2 ) 2 ]Cl. Triphenyl-phosphine and -arsine, and also bis( p -methoxyphenyl)tellurium(II) react with 1 in the same way. Conductivity and molecular weight data show that the benzoyl derivatives exist in solution as monomeric species. The metal-acyl bond in the compounds is stable towards MeOH, MeI, and CdX 2 . Reactions of 1 with triphenylbismuth leads to the cleavage of one Bi-Ph bond. Attempts to prepare the benzoyl derivative, Ph 3 PbCOC 6 H 3 (NO 2 ) 2 , by the reaction of 1 with hexaphenyldilead were unsuccessful, but one PbPh bond was cleaved of Ph 4 Pb in the presence of 1 .

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.

Organotellurium cations: organotellurium perchlorates and their complexes with Lewis bases

Abstract Solutions of diorganotellurium(IV) diperchlorates R2Te(ClO4)2 (where R = Ph, p-CH3OC6H4, R2Te = C 4 H 8 Te ) may be prepared by the reaction of R2TeCl2 and AgClO4 or by the reaction of diorganyltelluroxide with excess of 70% HClO4.IR and conductivity data indicate that Ph2Te(ClO4)2 possesses covalently bonded perchlorate groups in solution. Interaction of the freshly prepared solutions with Lewis bases affords cationic complexes of the types [R2Te(ClO4)(L)][ClO4] and [R2Te(L)2][ClO4]2 which have been characterised by IR elemental analyses and conductivity measurements.

Some Triphenylphosphinimine Derivatives of Group IV and V Metals

Abstract A few triphenylphosphinimine derivatives of group IV and V of the type Ph3M[N=PPh3]n (M=Sb or Bi; n=2 and M=Ge, Sn or Pb; n=1) have been synthesized. The metal-nitrogen bond(s) is (are) stable towards protic compounds like water, methanol or phenylacetylene, but is readily cleaved by TeCl4 and PhTeCl3.

Synthesis of Triarylantimony(V) Diamides

Abstract Five-coordinate organoantimony diamides of the type Ar3Sb(NR2)2 (Ar = phenyl, p-tolyl; HNR2 = succinimide, phthalimide, N-bromobenzami de, benzoxazones, benzoxazole-2-thione, benzimidazoles, benzotriazoles) have been isolated and characterised. Br2 and TeCl4 cleave Sb-N bonds in preference to Sb-Ar bonds. However, these amides ramain unaffected in the presence of MeOH or CS2. A few representative compounds were examined for biocidal property and were found to possess only moderate insecticidal but significant bactericidal activity.