8 research outputs found

    Fast and Reasonable Geometry Optimization of Lanthanoid Complexes with an Extended Tight Binding Quantum Chemical Method

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    The recently developed tight binding electronic structure approach GFN-xTB is tested in a comprehensive and diverse lanthanoid geometry optimization benchmark containing 80 lanthanoid complexes. The results are evaluated with reference to high-quality X-ray molecular structures obtained from the Cambridge Structural Database and theoretical DFT-D3­(BJ) optimized structures for a few Pm (<i>Z</i> = 61) containing systems. The average structural heavy-atom root-mean-square deviation of GFN-xTB (0.65 Å) is smaller compared to its competitors, the Sparkle/PM6 (0.86 Å) and HF-3c (0.68 Å) quantum chemical methods. It is shown that GFN-xTB yields chemically reasonable structures, less outliers, and performs well in terms of overall computational speed compared to other low-cost methods. The good reproduction of large lanthanoid complex structures corroborates the wide applicability of the GFN-xTB approach and its value as an efficient low-cost quantum chemical method. Its main purpose is the search for energetically low-lying complex conformations in the elucidation of reaction mechanisms

    C–F/C–H Functionalization by Manganese(I) Catalysis: Expedient (Per)Fluoro-Allylations and Alkenylations

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    C–F/C–H functionalizations proved to be viable within a versatile manganese­(I) catalysis manifold. Thus, a wealth of fluorinated alkenes were employed in C–F/C–H functionalizations through facile C–H activation. The robust nature of the manganese­(I) catalysis regime was among others reflected by the first C–F/C–H activation with perfluoroalkenes as well as racemization-free C–H functionalizations on imines, amino acids, and peptides

    Trapping Experiments on a Trichlorosilanide Anion: a Key Intermediate of Halogenosilane Chemistry

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    Treatment of Si<sub>2</sub>Cl<sub>6</sub> with [Et<sub>4</sub>N]­[BCl<sub>4</sub>] in CH<sub>2</sub>Cl<sub>2</sub> furnished the known products of a chloride-induced disproportionation reaction of the disilane, such as SiCl<sub>4</sub>, [Si­(SiCl<sub>3</sub>)<sub>3</sub>]<sup>−</sup>, and [Si<sub>6</sub>Cl<sub>12</sub>·2Cl]<sup>2–</sup>. No Si–B-bonded products were detectable. In contrast, the addition of Si<sub>2</sub>Cl<sub>6</sub> to [Et<sub>4</sub>N]­[BI<sub>3</sub>Cl] afforded the Si–B adduct [Et<sub>4</sub>N]­[I<sub>3</sub>SiBI<sub>3</sub>]. Thus, a quantitative Cl/I exchange at the silicon atom accompanies the trihalogenosilanide formation. [Et<sub>4</sub>N]­[I<sub>3</sub>SiBI<sub>3</sub>] was also accessible from a mixture of Si<sub>2</sub>I<sub>6</sub>, [Et<sub>4</sub>N]­I, and BI<sub>3</sub>. According to X-ray crystallography, the anion [I<sub>3</sub>SiBI<sub>3</sub>]<sup>−</sup> adopts a staggered conformation with an Si–B bond length of 1.977(6) Å. Quantum-chemical calculations revealed a polar covalent Si–B bond with significant contributions from intramolecular I···I dispersion interactions

    Counterintuitive Interligand Angles in the Diaryls E{C<sub>6</sub>H<sub>3</sub>‑2,6-(C<sub>6</sub>H<sub>2</sub>‑2,4,6‑<sup><i>i</i></sup>Pr<sub>3</sub>)<sub>2</sub>}<sub>2</sub> (E = Ge, Sn, or Pb) and Related Species: The Role of London Dispersion Forces

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    The straightforward reaction of two equivalents of the lithium salt of the bulky terphenyl ligand Li­(OEt<sub>2</sub>)­C<sub>6</sub>H<sub>3</sub>-2,6-(C<sub>6</sub>H<sub>2</sub>-2,4,6-<sup><i>i</i></sup>Pr<sub>3</sub>)<sub>2</sub> with suspensions of GeCl<sub>2</sub>·dioxane, SnCl<sub>2</sub>, or PbBr<sub>2</sub> in diethyl ether resulted in the isolation of the very crowded σ-bonded diaryl tetrylenes of formula E­{C<sub>6</sub>H<sub>3</sub>-2,6-(C<sub>6</sub>H<sub>2</sub>-2,4,6-<sup><i>i</i></sup>Pr<sub>3</sub>)<sub>2</sub>}<sub>2</sub> (E = Ge (<b>1</b>), Sn (<b>2</b>), Pb (<b>3</b>)) as blue crystalline solids. Despite their high level of steric congestion, X-ray crystallography showed that compounds <b>1</b>–<b>3</b> possess C<sub>ipso</sub>–E–C<sub>ipso</sub> interligand bond angles in the range 107.61–112.55°, which are narrower than those observed in analogous species with less bulky terphenyl substituents. Compounds <b>1</b>–<b>3</b> were characterized by <sup>1</sup>H, <sup>13</sup>C­{<sup>1</sup>H} (<b>1</b>–<b>3</b>), and <sup>119</sup>Sn­{<sup>1</sup>H} (<b>2</b>) NMR spectroscopy, whereas solution <sup>207</sup>Pb­{<sup>1</sup>H} NMR spectroscopy of <b>3</b> has not yet afforded a signal under ambient conditions. FT-IR and UV–vis spectra of <b>1</b>–<b>3</b> were also recorded. The relatively narrow interligand angles displayed by <b>1</b>–<b>3</b> are attributed in part to the increase in London dispersion force interactions between the two Ar<sup><i>i</i>Pr6</sup> (Ar<sup><i>i</i>Pr6</sup> = -C<sub>6</sub>H<sub>3</sub>-2,6-(C<sub>6</sub>H<sub>2</sub>-2,4,6-<sup><i>i</i></sup>Pr<sub>3</sub>)<sub>2</sub>) groups from carbon atoms in some of the isopropyl substituents and several carbon atoms from the flanking aryl rings. Density functional theory (DFT) calculations carried out at the PBE0/def2-QZVP level on the full series of diaryl tetrylenes, E­(Ar<sup><i>i</i>Pr6</sup>)<sub>2</sub>, E­(Ar<sup><i>i</i>Pr4</sup>)<sub>2</sub> (Ar<sup><i>i</i>Pr4</sup> = -C<sub>6</sub>H<sub>3</sub>-2,6-(C<sub>6</sub>H<sub>3</sub>-2,6-<sup><i>i</i></sup>Pr<sub>2</sub>)<sub>2</sub>), and E­(Ar<sup>Me6</sup>)<sub>2</sub> (Ar<sup>Me6</sup> = -C<sub>6</sub>H<sub>3</sub>-2,6-(C<sub>6</sub>H<sub>2</sub>-2,4,6-Me<sub>3</sub>)<sub>2</sub>, afford interaction energies as high as ca. 27 kcal mol<sup>–1</sup>

    Counterintuitive Interligand Angles in the Diaryls E{C<sub>6</sub>H<sub>3</sub>‑2,6-(C<sub>6</sub>H<sub>2</sub>‑2,4,6‑<sup><i>i</i></sup>Pr<sub>3</sub>)<sub>2</sub>}<sub>2</sub> (E = Ge, Sn, or Pb) and Related Species: The Role of London Dispersion Forces

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    The straightforward reaction of two equivalents of the lithium salt of the bulky terphenyl ligand Li­(OEt<sub>2</sub>)­C<sub>6</sub>H<sub>3</sub>-2,6-(C<sub>6</sub>H<sub>2</sub>-2,4,6-<sup><i>i</i></sup>Pr<sub>3</sub>)<sub>2</sub> with suspensions of GeCl<sub>2</sub>·dioxane, SnCl<sub>2</sub>, or PbBr<sub>2</sub> in diethyl ether resulted in the isolation of the very crowded σ-bonded diaryl tetrylenes of formula E­{C<sub>6</sub>H<sub>3</sub>-2,6-(C<sub>6</sub>H<sub>2</sub>-2,4,6-<sup><i>i</i></sup>Pr<sub>3</sub>)<sub>2</sub>}<sub>2</sub> (E = Ge (<b>1</b>), Sn (<b>2</b>), Pb (<b>3</b>)) as blue crystalline solids. Despite their high level of steric congestion, X-ray crystallography showed that compounds <b>1</b>–<b>3</b> possess C<sub>ipso</sub>–E–C<sub>ipso</sub> interligand bond angles in the range 107.61–112.55°, which are narrower than those observed in analogous species with less bulky terphenyl substituents. Compounds <b>1</b>–<b>3</b> were characterized by <sup>1</sup>H, <sup>13</sup>C­{<sup>1</sup>H} (<b>1</b>–<b>3</b>), and <sup>119</sup>Sn­{<sup>1</sup>H} (<b>2</b>) NMR spectroscopy, whereas solution <sup>207</sup>Pb­{<sup>1</sup>H} NMR spectroscopy of <b>3</b> has not yet afforded a signal under ambient conditions. FT-IR and UV–vis spectra of <b>1</b>–<b>3</b> were also recorded. The relatively narrow interligand angles displayed by <b>1</b>–<b>3</b> are attributed in part to the increase in London dispersion force interactions between the two Ar<sup><i>i</i>Pr6</sup> (Ar<sup><i>i</i>Pr6</sup> = -C<sub>6</sub>H<sub>3</sub>-2,6-(C<sub>6</sub>H<sub>2</sub>-2,4,6-<sup><i>i</i></sup>Pr<sub>3</sub>)<sub>2</sub>) groups from carbon atoms in some of the isopropyl substituents and several carbon atoms from the flanking aryl rings. Density functional theory (DFT) calculations carried out at the PBE0/def2-QZVP level on the full series of diaryl tetrylenes, E­(Ar<sup><i>i</i>Pr6</sup>)<sub>2</sub>, E­(Ar<sup><i>i</i>Pr4</sup>)<sub>2</sub> (Ar<sup><i>i</i>Pr4</sup> = -C<sub>6</sub>H<sub>3</sub>-2,6-(C<sub>6</sub>H<sub>3</sub>-2,6-<sup><i>i</i></sup>Pr<sub>2</sub>)<sub>2</sub>), and E­(Ar<sup>Me6</sup>)<sub>2</sub> (Ar<sup>Me6</sup> = -C<sub>6</sub>H<sub>3</sub>-2,6-(C<sub>6</sub>H<sub>2</sub>-2,4,6-Me<sub>3</sub>)<sub>2</sub>, afford interaction energies as high as ca. 27 kcal mol<sup>–1</sup>

    Exhaustively Trichlorosilylated C<sub>1</sub> and C<sub>2</sub> Building Blocks: Beyond the Müller–Rochow Direct Process

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    The Cl<sup>–</sup>-induced heterolysis of the Si–Si bond in Si<sub>2</sub>Cl<sub>6</sub> generates an [SiCl<sub>3</sub>]<sup>−</sup> ion as reactive intermediate. When carried out in the presence of CCl<sub>4</sub> or Cl<sub>2</sub>CCCl<sub>2</sub> (CH<sub>2</sub>Cl<sub>2</sub> solutions, room temperature or below), the reaction furnishes the monocarbanion [C­(SiCl<sub>3</sub>)<sub>3</sub>]<sup>−</sup> ([<b>A</b>]<sup>−</sup>; 92%) or the vicinal dianion [(Cl<sub>3</sub>Si)<sub>2</sub>C–C­(SiCl<sub>3</sub>)<sub>2</sub>]<sup>2–</sup> ([<b>B</b>]<sup>2–</sup>; 85%) in excellent yields. Starting from [<b>B</b>]<sup>2–</sup>, the tetrasilylethane (Cl<sub>3</sub>Si)<sub>2</sub>(H)­C–C­(H)­(SiCl<sub>3</sub>)<sub>2</sub> (H<sub>2</sub><b>B</b>) and the tetrasilylethene (Cl<sub>3</sub>Si)<sub>2</sub>CC­(SiCl<sub>3</sub>)<sub>2</sub> (<b>B</b>; 96%) are readily available through protonation (CF<sub>3</sub>SO<sub>3</sub>H) or oxidation (CuCl<sub>2</sub>), respectively. Equimolar mixtures of H<sub>2</sub><b>B</b>/[<b>B</b>]<sup>2–</sup> or <b>B</b>/[<b>B</b>]<sup>2–</sup> quantitatively produce 2 equiv of the monoanion [H<b>B</b>]<sup>−</sup> or the blue radical anion [<b>B</b><sup><b>•</b></sup>]<sup>−</sup>, respectively. Treatment of <b>B</b> with Cl<sup>–</sup> ions in the presence of CuCl<sub>2</sub> furnishes the disilylethyne Cl<sub>3</sub>SiCCSiCl<sub>3</sub> (<b>C</b>; 80%); in the presence of [HMe<sub>3</sub>N]­Cl, the trisilylethene (Cl<sub>3</sub>Si)<sub>2</sub>CC­(H)­SiCl<sub>3</sub> (<b>D</b>; 72%) is obtained. Alkyne <b>C</b> undergoes a [4+2]-cycloaddition reaction with 2,3-dimethyl-1,3-butadiene (CH<sub>2</sub>Cl<sub>2</sub>, 50 °C, 3d) and thus provides access to 1,2-bis­(trichlorosilyl)-4,5-dimethylbenzene (<b>E1</b>; 80%) after oxidation with DDQ. The corresponding 1,2-bis­(trichlorosilyl)-3,4,5,6-tetraphenylbenzene (<b>E2</b>; 83%) was prepared from <b>C</b> and 2,3,4,5-tetraphenyl-2,4-cyclopentadien-1-one under CO extrusion at elevated temperatures (CH<sub>2</sub>Cl<sub>2</sub>, 180 °C, 4 d). All closed-shell products were characterized by <sup>1</sup>H, <sup>13</sup>C­{<sup>1</sup>H}, and <sup>29</sup>Si NMR spectroscopy; an EPR spectrum of [<i>n</i>Bu<sub>4</sub>N]­[<b>B</b><sup><b>•</b></sup>] was recorded. The molecular structures of [<i>n</i>Bu<sub>4</sub>N]­[<b>A</b>], [<i>n</i>Bu<sub>4</sub>N]<sub>2</sub>[<b>B</b>], <b>B</b>, <b>E1</b>, and <b>E2</b> were further confirmed by single-crystal X-ray diffraction. On the basis of detailed experimental investigations, augmented by quantum-chemical calculations, plausible reaction mechanisms for the formation of [<b>A</b>]<sup>−</sup>, [<b>B</b>]<sup>2–</sup>, <b>C</b>, and <b>D</b> are postulated

    Exhaustively Trichlorosilylated C<sub>1</sub> and C<sub>2</sub> Building Blocks: Beyond the Müller–Rochow Direct Process

    No full text
    The Cl<sup>–</sup>-induced heterolysis of the Si–Si bond in Si<sub>2</sub>Cl<sub>6</sub> generates an [SiCl<sub>3</sub>]<sup>−</sup> ion as reactive intermediate. When carried out in the presence of CCl<sub>4</sub> or Cl<sub>2</sub>CCCl<sub>2</sub> (CH<sub>2</sub>Cl<sub>2</sub> solutions, room temperature or below), the reaction furnishes the monocarbanion [C­(SiCl<sub>3</sub>)<sub>3</sub>]<sup>−</sup> ([<b>A</b>]<sup>−</sup>; 92%) or the vicinal dianion [(Cl<sub>3</sub>Si)<sub>2</sub>C–C­(SiCl<sub>3</sub>)<sub>2</sub>]<sup>2–</sup> ([<b>B</b>]<sup>2–</sup>; 85%) in excellent yields. Starting from [<b>B</b>]<sup>2–</sup>, the tetrasilylethane (Cl<sub>3</sub>Si)<sub>2</sub>(H)­C–C­(H)­(SiCl<sub>3</sub>)<sub>2</sub> (H<sub>2</sub><b>B</b>) and the tetrasilylethene (Cl<sub>3</sub>Si)<sub>2</sub>CC­(SiCl<sub>3</sub>)<sub>2</sub> (<b>B</b>; 96%) are readily available through protonation (CF<sub>3</sub>SO<sub>3</sub>H) or oxidation (CuCl<sub>2</sub>), respectively. Equimolar mixtures of H<sub>2</sub><b>B</b>/[<b>B</b>]<sup>2–</sup> or <b>B</b>/[<b>B</b>]<sup>2–</sup> quantitatively produce 2 equiv of the monoanion [H<b>B</b>]<sup>−</sup> or the blue radical anion [<b>B</b><sup><b>•</b></sup>]<sup>−</sup>, respectively. Treatment of <b>B</b> with Cl<sup>–</sup> ions in the presence of CuCl<sub>2</sub> furnishes the disilylethyne Cl<sub>3</sub>SiCCSiCl<sub>3</sub> (<b>C</b>; 80%); in the presence of [HMe<sub>3</sub>N]­Cl, the trisilylethene (Cl<sub>3</sub>Si)<sub>2</sub>CC­(H)­SiCl<sub>3</sub> (<b>D</b>; 72%) is obtained. Alkyne <b>C</b> undergoes a [4+2]-cycloaddition reaction with 2,3-dimethyl-1,3-butadiene (CH<sub>2</sub>Cl<sub>2</sub>, 50 °C, 3d) and thus provides access to 1,2-bis­(trichlorosilyl)-4,5-dimethylbenzene (<b>E1</b>; 80%) after oxidation with DDQ. The corresponding 1,2-bis­(trichlorosilyl)-3,4,5,6-tetraphenylbenzene (<b>E2</b>; 83%) was prepared from <b>C</b> and 2,3,4,5-tetraphenyl-2,4-cyclopentadien-1-one under CO extrusion at elevated temperatures (CH<sub>2</sub>Cl<sub>2</sub>, 180 °C, 4 d). All closed-shell products were characterized by <sup>1</sup>H, <sup>13</sup>C­{<sup>1</sup>H}, and <sup>29</sup>Si NMR spectroscopy; an EPR spectrum of [<i>n</i>Bu<sub>4</sub>N]­[<b>B</b><sup><b>•</b></sup>] was recorded. The molecular structures of [<i>n</i>Bu<sub>4</sub>N]­[<b>A</b>], [<i>n</i>Bu<sub>4</sub>N]<sub>2</sub>[<b>B</b>], <b>B</b>, <b>E1</b>, and <b>E2</b> were further confirmed by single-crystal X-ray diffraction. On the basis of detailed experimental investigations, augmented by quantum-chemical calculations, plausible reaction mechanisms for the formation of [<b>A</b>]<sup>−</sup>, [<b>B</b>]<sup>2–</sup>, <b>C</b>, and <b>D</b> are postulated

    CO-Reduction Chemistry: Reaction of a CO-Derived Formylhydridoborate with Carbon Monoxide, with Carbon Dioxide, and with Dihydrogen

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    Treatment of the bulky metallocene hydride Cp*<sub>2</sub>Zr­(H)­OMes (Cp* = pentamethyl­cyclopentadienyl, Mes = mesityl) with Piers’ borane [HB­(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub>] and carbon monoxide (CO) gave the formylhydridoborate complex [Zr]–OCH–BH­(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> ([Zr] = Cp*<sub>2</sub>Zr–OMes). From the dynamic NMR behavior, its endergonic equilibration with the [Zr]–O–CH<sub>2</sub>–B­(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> isomer was deduced, which showed typical reactions of an oxygen/boron frustrated Lewis pair. It was trapped with CO to give an O–[Zr] bonded borata-β-lactone. Trapping with carbon dioxide (CO<sub>2</sub>) gave the respective O–[Zr] bonded cyclic boratacarbonate product. These reaction pathways were analyzed by density functional theory calculation. The formylhydridoborate complex was further reduced by dihydrogen via two steps; it reacted rapidly with H<sub>2</sub> to give Cp*<sub>2</sub>Zr­(OH)­OMes and H<sub>3</sub>C–B­(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub>, which then slowly reacted further with H<sub>2</sub> to eventually give [Zr]–O­(H)–B­(H)­(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> and methane (CH<sub>4</sub>). Most complexes were characterized by X-ray diffraction
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