Pamela Finke

Well-Defined Stibonic and Tellurinic Acids

The first stibonic acids RSb(O)(OH)2 [1] and tellurinic acids RTe(O)(OH) (R = aryl, alkyl) were extensively investigated more than 90 years ago in the context of pharmacological studies on arsonic acids RAs(O)(OH)2 and the closely related remedies atoxyl and salvarsan, marking the beginning of modern chemotherapy. Unlike their lighter Group 15 and 16 congeners, all hitherto described stibonic and tellurinic acids are ill-defined, amorphous, high-melting compounds that are poorly soluble in most organic solvents. Molecular weight determinations and Sb M ssbauer spectroscopic studies confirm a high degree of aggregation and a trigonalbipyramidal structure for PhSb(O)(OH)2. By contrast, all phosphonic and arsonic acids RE(O)(OH)2 (E = P, As), as well as sulfinic and seleninic acids RE(O)(OH) (E = S, Se), are well-defined molecular compounds with tetrahedrally coordinated central atoms E, polar (formal) E=O double bonds and E OH groups that are usually involved in intermolecular hydrogen bonding in the solid state. Aggregation was also observed for related triarylantimony oxides and diaryltellurium oxides, which exist in two distinctively different structures, namely as asymmetric dimers, for example (Ph3SbO)2 [6] and (Ph2TeO)2 , [7] and as one-dimensional polymers, for example, (Ph3SbO)n [8] and (pAns2TeO)n (Ans = MeOC6H4). [9]

Mesityltellurenyl Cations Stabilized by Triphenylpnictogens [MesTe(EPh3)]+ (E = P, As, Sb)

The homoleptic 1:1 Lewis pair (LP) complex [MesTe(TeMes2)]O3SCF3 (1) featuring the cation [MesTe(TeMes2)](+) (1a) was obtained by the reaction of Mes2Te with HO3SCF3. The reaction of 1 with Ph3E (E = P, As, Sb, Bi) proceeded with substitution of Mes2Te and provided the heteroleptic 1:1 LP complexes [MesTe(EPh3)]O3SCF3 (2, E = P; 3, E = As) and [MesTe(SbPh3)][Ph2Sb(O3SCF3)2] (4) featuring the cations [MesTe(EPh3)](+) (2a, E = P; 3a, E = As; 4a, E = Sb) and the anion [Ph2Sb(O3SCF3)2](-) (4b). In the reaction with Ph3Bi, the crude product contained the cation [MesTe(BiPh3)](+) (5a) and the anion [Ph2Bi(O3SCF3)2](-) (5b); however, the heteroleptic 1:1 LP complex [MesTe(BiPh3)][Ph2Bi(O3SCF3)2] (5) could not be isolated because of its limited stability. Instead, fractional crystallization furnished a large amount of Ph2BiO3SCF3 (6), which was also obtained by the reaction of Ph3Bi with HO3SCF3. The formation of the anions 4b and 5b involves a phenyl group migration from Ph3E (E = Sb, Bi) to the MesTe(+) cation and afforded MesTePh as the byproduct, which was identified in the mother liquor. The heteroleptic 1:1 LP complexes 2-4 were also obtained by the one-pot reaction of Mes2Te, Ph3E (E = P, As, Sb) and HO3SCF3. Compounds 1-4 and 6 were investigated by single-crystal X-ray diffraction. The molecular structures of 1a-4a were used for density functional theory calculations at the B3PW91/TZ level of theory and studied using natural bond order (NBO) analyses as well as real-space bonding descriptors derived from an atoms-in-molecules (AIM) analysis of the theoretically obtained electron density. Additionally, the electron localizability indicator (ELI-D) and the delocalization index are derived from the corresponding pair density.

Diarylhalotelluronium(IV) cations [(8-Me2NC10H6)2TeX]+ (X = Cl, Br, I) stabilized by intramolecularly coordinating N-donor substituents

The stoichiometrically controlled halogenation of the intramolecularly coordinated diaryltelluride (8-Me2NC10H6)2Te using SO2Cl2, Br2 and I2 was studied. At an equimolar ratio, the diarylhalotelluronium cations [(8-Me2NC10H6)2TeX](+) (1, X = Cl; 2, X = Br; 3, X = I) formed and were isolated as 1·Cl(-)·H2O·1/2THF, 2·Br(-), and 3·I(-), respectively. When the same reactions were carried out in the presence of KPF6, 1·PF6(-) and 22·Br(-)·PF6(-) were obtained. The chlorination of (8-Me2NC10H6)2Te with an excess of SO2Cl2 occurred with a double electrophilic substitution at the 8-dimethylaminonaphthyl residues (in the ortho- and para-positions) and afforded the diaryltellurium dichloride (5,7-Cl2-8-Me2NC10H4)2TeCl2 (4). The bromination of (8-Me2NC10H6)2Te with three equivalents of Br2 took place with a single electrophilic substitution at the 8-dimethylaminonaphthyl residues (in the para-positions) and provided the diaryltellurium dibromide (5-Br-8-Me2NC10H5)2TeBr2 (5), while an excess of Br2 produced the diarylbromotelluronium cation [(5-Br-8-Me2NC10H5)2TeBr](+) (6) that was isolated as 6·Br3(-). The reaction of (8-Me2NC10H6)2Te with two or three equivalents of iodine provided 3·I3(-) and 3·I3(-)·I2, respectively. In the presence of water, 1·Cl(-)·H2O·1/2THF, 2·Br(-), 3·I(-) and 3·I3(-) hydrolyzed to give the previously known diarylhydroxytelluronium cation [(8-Me2NC10H6)2TeOH](+) (7) that was isolated as 7·Cl(-), 7·Br(-)·H2O·THF, 7·I(-) and 7·I3(-)·H2O, respectively. The molecular structures of 1-7 were investigated in the solid-state by (125)Te MAS NMR spectroscopy and X-ray crystallography and in solution by multinuclear NMR spectroscopy ((1)H, (13)C, (125)Te), electrospray mass spectrometry and conductivity measurements. The stabilization of cations 1-3 by the intramolecular coordination was estimated by DFT calculations at the B3PW91/TZ level of theory.

Oxygen Transfer from an Intramolecularly Coordinated Diaryltellurium Oxide to Acetonitrile. Formation and Combined AIM and ELI-D Analysis of a Novel Diaryltellurium Acetimidate

The reaction of the intramolecularly coordinated diaryltellurium(IV) oxide (8-Me2NC10H6)2TeO with acetonitrile proceeds with oxygen transfer and gives rise to the formation of the novel zwitterionic diaryltelluronium(IV) acetimidate (8-Me2NC10H6)2TeNC(O)CH3 (1) in 57% yield. Hydrolysis of 1 with hydrochloric acid affords acetamide and the previously known diarylhydroxytelluronium(IV) chloride [(8-Me2NC10H6)2Te(OH)]Cl.