Phosphine and Diphosphine Complexes of Silicon(IV) Halides

The reaction of SiX₄ (X = Cl or Br) with PMe₃ in anhydrous CH₂Cl₂ forms <i>trans</i>-[SiX₄(PMe₃)₂], while the diphosphines, Me₂P­(CH₂)₂PMe₂, Et₂P­(CH₂)₂PEt₂, and <i>o</i>-C₆H₄(PMe₂)₂ form <i>cis</i>-[SiX₄(diphosphine)], all containing six-coordinate silicon centers. With Me₂PCH₂PMe₂ the product was <i>trans</i>-[SiCl₄(κ¹-Me₂PCH₂PMe₂)₂]. The complexes have been characterized by X-ray crystallography, microanalysis, IR, and multinuclear (¹H, ¹³C­{¹H}, and ³¹P­{¹H}) NMR spectroscopies. The complexes are stable solids and not significantly dissociated in nondonor solvents, although they are very moisture and oxygen sensitive. This stability conflicts with the predictions of recent density functional theory (DFT) calculations (Wilson et al.<i> Inorg. Chem</i>. <b>2012</b>, <i>51</i>, 7657–7668) which suggested six-coordinate silicon phosphines would be unstable, and also contrasts with the failure to isolate complexes with SiF₄ (George et al.<i> Dalton Trans</i>. <b>2011</b>, <i>40,</i> 1584–1593). No reaction occurred between phosphines and SiI₄, or with SiX₄ and arsine ligands including AsMe₃ and <i>o</i>-C₆H₄(AsMe₂)₂. Attempts to make five-coordinate [SiX₄(PR₃)] using the sterically bulky phosphines, P^tBu₃, PⁱPr₃, or PCy₃ failed, with no apparent reaction occurring, consistent with predictions (Wilson et al. <i>Inorg. Chem</i>. <b>2012</b>, <i>51</i>, 7657–7668) that such compounds would be very endothermic, while the large cone angles of the phosphines presumably preclude formation of six-coordination at the small silicon center. The reaction of Si₂Cl₆ with PMe₃ or the diphosphines in CH₂Cl₂ results in instant disproportionation to the SiCl₄ adducts and polychlorosilanes, but from hexane solution very unstable white [Si₂Cl₆(PMe₃)₂] and [Si₂Cl₆(diphosphine)] (diphosphine = Me₂P­(CH₂)₂PMe₂ or <i>o</i>-C₆H₄(PMe₂)₂) precipitate. The reactions of SiHCl₃ with PMe₃ and Me₂P­(CH₂)₂PMe₂ also produce the SiCl₄ adducts, but using Et₂P­(CH₂)₂PEt₂, colorless [SiHCl₃{Et₂P­(CH₂)₂PEt₂}] was isolated, which was characterized by an X-ray structure which showed a pseudo-octahedral complex with the Si–H <i>trans</i> to P. Attempts to reduce the silicon­(IV) phosphine complexes to silicon­(II) were unsuccessful, contrasting with the isolation of stable N-heterocyclic carbene adducts of Si­(II)

Phosphine and Diphosphine Complexes of Silicon(IV) Halides

The reaction of SiX₄ (X = Cl or Br) with PMe₃ in anhydrous CH₂Cl₂ forms <i>trans</i>-[SiX₄(PMe₃)₂], while the diphosphines, Me₂P­(CH₂)₂PMe₂, Et₂P­(CH₂)₂PEt₂, and <i>o</i>-C₆H₄(PMe₂)₂ form <i>cis</i>-[SiX₄(diphosphine)], all containing six-coordinate silicon centers. With Me₂PCH₂PMe₂ the product was <i>trans</i>-[SiCl₄(κ¹-Me₂PCH₂PMe₂)₂]. The complexes have been characterized by X-ray crystallography, microanalysis, IR, and multinuclear (¹H, ¹³C­{¹H}, and ³¹P­{¹H}) NMR spectroscopies. The complexes are stable solids and not significantly dissociated in nondonor solvents, although they are very moisture and oxygen sensitive. This stability conflicts with the predictions of recent density functional theory (DFT) calculations (Wilson et al.<i> Inorg. Chem</i>. <b>2012</b>, <i>51</i>, 7657–7668) which suggested six-coordinate silicon phosphines would be unstable, and also contrasts with the failure to isolate complexes with SiF₄ (George et al.<i> Dalton Trans</i>. <b>2011</b>, <i>40,</i> 1584–1593). No reaction occurred between phosphines and SiI₄, or with SiX₄ and arsine ligands including AsMe₃ and <i>o</i>-C₆H₄(AsMe₂)₂. Attempts to make five-coordinate [SiX₄(PR₃)] using the sterically bulky phosphines, P^tBu₃, PⁱPr₃, or PCy₃ failed, with no apparent reaction occurring, consistent with predictions (Wilson et al. <i>Inorg. Chem</i>. <b>2012</b>, <i>51</i>, 7657–7668) that such compounds would be very endothermic, while the large cone angles of the phosphines presumably preclude formation of six-coordination at the small silicon center. The reaction of Si₂Cl₆ with PMe₃ or the diphosphines in CH₂Cl₂ results in instant disproportionation to the SiCl₄ adducts and polychlorosilanes, but from hexane solution very unstable white [Si₂Cl₆(PMe₃)₂] and [Si₂Cl₆(diphosphine)] (diphosphine = Me₂P­(CH₂)₂PMe₂ or <i>o</i>-C₆H₄(PMe₂)₂) precipitate. The reactions of SiHCl₃ with PMe₃ and Me₂P­(CH₂)₂PMe₂ also produce the SiCl₄ adducts, but using Et₂P­(CH₂)₂PEt₂, colorless [SiHCl₃{Et₂P­(CH₂)₂PEt₂}] was isolated, which was characterized by an X-ray structure which showed a pseudo-octahedral complex with the Si–H <i>trans</i> to P. Attempts to reduce the silicon­(IV) phosphine complexes to silicon­(II) were unsuccessful, contrasting with the isolation of stable N-heterocyclic carbene adducts of Si­(II)

Group 13 β-Ketoiminate Compounds: Gallium Hydride Derivatives As Molecular Precursors to Thin Films of Ga₂O₃

Bis­(β-ketoimine) ligands, [R­{N­(H)­C­(Me)-CHC­(Me)O}₂] (<b>L</b>_<b>1</b><b>H</b>_<b>2</b>, R = (CH₂)₂; <b>L</b>_<b>2</b><b>H</b>_<b>2</b>, R = (CH₂)₃), linked by ethylene (<b>L</b>_<b>1</b>) and propylene (<b>L</b>_<b>2</b>) bridges have been used to form aluminum, gallium, and indium chloride complexes [Al­(L₁)­Cl] (<b>3</b>), [Ga­(L_<i>n</i>)­Cl] (<b>4</b>, <i>n</i> = 1; <b>6</b>, <i>n</i> = 2) and [In­(L_<i>n</i>)­Cl] (<b>5</b>, <i>n</i> = 1; <b>7</b>, <i>n</i> = 2). Ligand <b>L</b>_<b>1</b> has also been used to form a gallium hydride derivative [Ga­(L₁)­H] (<b>8</b>), but indium analogues could not be made. β-ketoimine ligands, [Me₂N­(CH₂)₃N­(H)­C­(R′)-CHC­(R′)O] (<b>L</b>_<b>3</b><b>H</b>, R′ = Me; <b>L</b>_<b>4</b><b>H</b>, R′ = Ph), with a donor-functionalized Lewis base have also been synthesized and used to form gallium and indium alkyl complexes, [Ga­(L₃)­Me₂] (<b>9</b>) and [In­(L₃)­Me₂] (<b>10</b>), which were isolated as oils. The related gallium hydride complexes, [Ga­(L_<i>n</i>)­H₂] (<b>11</b>, <i>n</i> = 3; <b>12</b>, <i>n</i> = 4), were also prepared, but again no indium hydride species could be made. The complexes were characterized mainly by NMR spectroscopy, mass spectrometry, and single crystal X-ray diffraction. The β-ketoiminate gallium hydride compounds (<b>8</b> and <b>11</b>) have been used as single-source precursors for the deposition of Ga₂O₃ by aerosol-assisted (AA)­CVD with toluene as the solvent. The quality of the films varied according to the precursor used, with the complex [Ga­(L₁)­H] (<b>8</b>) giving by far the best quality films. Although the films were amorphous as deposited, they could be annealed at 1000 °C to form crystalline Ga₂O₃. The films were analyzed by powder XRD, SEM, and EDX

Tetramethyl Orthosilicate (TMOS) as a Reagent for Direct Amidation of Carboxylic Acids

Tetramethyl orthosilicate (TMOS) is shown to be an effective reagent for direct amidation of aliphatic and aromatic carboxylic acids with amines and anilines. The amide products are obtained in good to quantitative yields in pure form directly after workup without the need for any further purification. A silyl ester as the putative activated intermediate is observed by NMR methods. Amidations on a 1 mol scale are demonstrated with a favorable process mass intensity

Social Media Marketing und Kapitalisierungsmöglichkeiten im Spitzensport Eine empirische Erfolgsfaktorenanalyse im Rahmen der 1. Fußball-Bundesliga

Unprecedented homoleptic octathioether macrocyclic coordination to Na⁺ in [Na([24]­aneS₈)]⁺ has been achieved by using Na­[B­{3,5-(CF₃)₂-C₆H₃}₄] as a source of “naked” Na⁺ ions and confirmed crystallographically, with <i>d</i>(Na–S) = 2.9561(15)–3.0524(15) Å. Density functional theory calculations show that there is electron transfer from the S 3p and C 2p valence orbitals of the ligand to the 3s and 3p orbitals of the Na⁺ ion upon complexation

Metal–Organic Frameworks Constructed from Group 1 Metals (Li, Na) and Silicon-Centered Linkers

A series of “light metal” metal–organic frameworks containing secondary building units (SBUs) based on Li⁺ and Na⁺ cations have been prepared using the silicon-centered linkers Me_<i>x</i>Si­(<i>p</i>-C₆H₄CO₂H)_4‑<i>x</i> (<i>x</i> = 2, 1, 0). The unipositive charge, small size, and oxophilic nature of the metal cations give rise to some unusual and unique SBUs, including a three-dimensional nodal structure built from sodium and oxygen ions when using the triacid linker (<i>x</i> = 1). The same linker with Li⁺ cations generated a chiral, helical SBU, formed from achiral starting materials. One-dimensional rod SBUs are observed for the diacid (<i>x</i> = 2) and tetra-acid (<i>x</i> = 0) linkers with both Li⁺ and Na⁺ cations, where the larger size of Na⁺ compared to Li⁺ leads to subtle differences in the constitution of the metal nodes