Synthesen und Kristallstrukturen von Dialkylgalliumhydriden — dimere versus trimere Formeleinheiten

Syntheses and Crystal Structures of Dialkylgallium Hydrides — Dimeric versus Trimeric Formula Units Dialkylgallium hydrides (R = Me, Et, iPr, iBu, neopentyl) were obtained on two different synthetic routes. The dimethyl and diethyl compounds were formed by the reaction of LiH with the corresponding dialkylgallium chlorides via lithium dialkyldihydridogallate intermediates, which so far have not been isolated in a pure form. On the second route, trialkylgallium compounds were treated with [GaH₃·NMe₂Et] to yield the dialkylgallium hydrides by a substituent exchange reaction. The dimethyl, diethyl and diisopropyl compounds are trimeric in solution. That trimeric structure was verified for the diisopropyl derivative by a crystal structure determination. Di(neopentyl)gallium hydride has a dimeric structure in solution and in the solid state.     

Pseudo‐Isomerie durch unterschiedliche Jahn‐Teller‐Ordnung: Die Kristallstrukturen des Hemihydrats und des Monohydrats von (pyH)[MnF(H2PO4)(HPO4)]

Pseudo‐Isomerism by Different Jahn‐Teller Ordering: Crystal Structures of the Hemihydrate and the Monohydrate of (pyH)[MnF(H₂PO₄)(HPO₄)] With pyridinium counter cations (pyH⁺) the Mn^III fluoride phosphate anion [MnF(H₂PO₄)(HPO₄)]^— can be stabilized. It forms a chain structure with Mn³⁺ ions bridged by a fluoride ion and two bidentate phosphate groups. Under sleightly differing conditions either the hemihydrate (pyH)[MnF(H₂PO₄)(HPO₄)]·0.5H₂O ( 1 ) or the monohydrate (pyH)[MnF(H₂PO₄)(HPO₄)]·H₂O ( 2 ) is formed. The hemihydrate 1 crystallizes monoclinic in space group P2₁/n, Z = 8, a = 7.295(1), b = 17.052(2), c = 18.512(3) Å, β = 100.78(1)°, R = 0.033, the monohydrate triclinic in space group P1¯, Z = 2, a = 7.374(1), b = 8.628(1), c = 10.329(1) Å, α = 83.658(8)°, β = 77.833(9)°, γ = 68.544(8)°, R = 0.025. Whereas the topology of the chain anions is identical in both structures, the Jahn‐Teller effect is expressed in different ordering patterns: in 1 antiferrodistortive ordering of [MnF₂O₄] octahedra is observed, with alternating elongation of an F—Mn—F‐axis or a O—Mn—O‐axis, respectively. This leads to asymmetrical Mn—F—Mn‐bridges. In 2 ferrodistortive ordering is found, with elongation of all octahedra along the F—Mn—F‐axis. Thus, symmetrical bridges are formed with long Mn—F distances. This unusual pseudo‐isomerism is attributed to the differing influence of inter‐chain hydrogen bonds.     

Die Umsetzung von Dialkylaluminiumchloriden mit Bis(trimethylsilyl)hydrazin: Bildung von Addukten R2AlCl · NH2NHSiMe3 mit dem thermisch unbeständigen Trimethylsilylhydrazin

The Reaction of Dialkylaluminium Chlorides with Bis(trimethylsilyl)hydrazine: Formation of the Adducts R₂AlCl · NH₂NHSiMe₃ Containing the Unstable Monotrimethylsilylhydrazine Bis(trimethylsilyl)hydrazine did not react with dialkylaluminium chlorides R₂AlCl [R = CH₂CMe₃, CMe₃ and CH(SiMe₃)₂] by the formation of trimethylchlorosilane, but by dismutation to yield tris(trimethylsilyl)hydrazine and trimethylsilylhydrazine. The unstable, sterically less shielded NH₂NHSiMe₃ was stabilized by the coordination to the coordinatively unsaturated aluminium compounds. The adducts R₂AlCl · NH₂NHSiMe₃ were formed, which were characterized by crystal structure determinations with R = CMe₃ and CH(SiMe₃)₂. In all cases, the hydrazine derivative binds to the aluminium atoms via the more basic NH₂ nitrogen atom. The adduct Me₃CAlCl₂ · NH₂N(SiMe₃)₂ containing intact 1,1‐bis(trimethylsilyl)hydrazine as a ligand was isolated in a trace amount and also characterized by a crystal structure determination.     

[ScCl2{N(SiMe3)2}(THF)2] als Vorläufer für die Synthese von Scandiumnitrid

[ScCl₂{N(SiMe₃)₂}(THF)₂] – a Precursor for the Synthesis of Scandium Nitride [ScCl₂{N(SiMe₃)₂}(THF)₂] ( 1 ) has been prepared by the reaction of [ScCl₃(THF)₃] with the trisamide Sc[N(SiMe₃)₂]₃ in tetrahydrofurane solution forming colourless moisture sensitive crystals, which were characterized by a crystal structure determination. Space group P 1, Z = 2, lattice dimensions at –50 °C: a = 841.4(1), b = 924.2(1), c = 1550.0(1) pm, α = 90.046(7)°, β = 95.671(9)°, γ = 106.066(6)°, R₁ = 0.0329. In the molecular structure of 1 the scandium atom has a distorted trigonal‐bipyramidal coordination with the THF molecules in apical positions. At 400 °C 1 is converted into scandium nitride, ScN, by stepwise leaving of THF and ClSiMe₃.     

Phosphoraneiminato Complexes of Manganese and Cobalt with Heterocubane Structure

The phosphoraneiminato complexes [MnBr(NPEt₃)]₄ ( 1 ) and [M₄Br₅{NP(NMe₂)₃}₃] with M = Mn ( 2 ) and M = Co ( 3 ) are prepared by melting reactions from the anhydrous metal dibromides with the silylated phosphaneimines Me₃SiNPR₃ (R = Et, NMe₂) in the presence of potassium fluoride. All complexes are characterized by crystal structure analyses. 1 forms an only slightly distorted Mn₄N₄ heterocubane skeleton with an approximate T_d symmetry and short Mn…Mn distances of average 295.7 pm. In the structures of 2 and 3 one μ₃-NPEt₃ ligand of 1 is replaced by one bromine atom with μ₃-function. This leads to the novel heterocubane type M₄N₃Br with approximate C₃ symmetry. The deformation of the cubic skeleton leads to metal-metal distances of different lengths, i. e. 292.7 and 323.6 pm in 2 and 274.4 and 306.2 pm in 3 . Temperature dependent magnetic susceptibility measurements between 300 and 5 K on 1 have shown that strong antiferromagnetic coupling exists between the Mn(II) ions with S = 5/2, with a large negative Weiss constant of Θ = –694 K.     

Die Deprotonierung silylierter Amido-Komplexe von Seltenerdelementen

Deprotonation Reactions of Silylated Amido Complexes of Rare Earth Elements The deprotonation of the rare earth element-tris(bistrimethylsilyl)amides Ln[N(SiMe₃)₂]₃ of scandium, ytterbium, and lutetium with sodium-bis(trimethylsilyl)amide in THF leads to the complexes [Na(THF)₃LnCH₂SiMe₂NSiMe₃{N(SiMe₃)₂}₂] [Ln = Sc ( 1 ), Yb ( 2 ), and Lu ( 3 )]. According to crystal structure analyses of 1 and 2 the metal atoms Sc and Yb are constituents of planar LnCSiN four-membered rings. At the same time, the C atom of the CH₂ group is coordinated with the sodium ion in a linear axis Ln–C–Na; the sodium ion obtains a distorted tetrahedral arrangement by three THF molecules. The equatorial positions of the methylene-C atom, which is coordinated in a trigonal bipyramidal fashion, are occupied by the two H atoms and the Si atom of the four-membered ring. 2.6-dimethylbenzoisonitrile can be inserted into the Yb–CH₂ bond of 2 and the new five-membered heterocylce YbNCSiN originates, the exocyclic CH₂ group of which enters into a C–C coupling with the centrosymmetric dimer 4 while the ytterbium undergoes reduction. At the same time, sodium-7-methyl indolate is formed, which together with [NaN(SiMe₃)₂(THF)₂] forms the centrosymmetric dimeric molecular aggregate [NaN(SiMe₃)₂(THF)₂Na(C₉H₁₆N)]₂ ( 5 ). 1 : Space group P2₁/n, Z = 8, lattice dimensions at –80 °C: a = 2941.4(2), b = 1205.5(1), c = 2952.4(3) pm; β = 113.455(8)°; R₁ = 0.0625. 2 : Space group P2₁/n, Z = 8, lattice dimensions at –80 °C: a = 2943.9(1), b = 1219.5(1), c = 2944.3(1) pm; β = 113.372(4)°; R₁ = 0.0361. 4 : Space group P 1, Z = 4, lattice dimensions at –80 °C: a = 1117.0(1), b = 1207.5(1), c = 1614.3(2) pm; α = 73.634(10)°, β = 82.091(10)°, γ = 74.391(10)°; R₁ = 0.0525. 5 : Space group P2₁/n, Z = 2, lattice dimensions at –80 °C: a = 1126.7(1), b = 1459.3(1), c = 1741.1(1) pm; β = 96.461(8)°; R₁ = 0.0458. Quantum chemical DFT calculations of the scandium model compound [Na(Me₂O)₃ScCH₂SiMe₂NSiH₃{N(SiH₃)₂}₂] ( 1 M ) give a very large negative charge at the pentacoordinated carbon atom of the four-membered ring that is concentrated in a lone-pair orbital which has mainly p character. The carbon atom interacts with the positively charged scandium atom mainly by Coulombic interactions.     

Hexasupersilyl-triprismo-hexastannane (tBu3Si)6Sn6—The First Molecular Tin Compound Containing a Sn6 Prism

Dark violet hexastannane ( t Bu ₃ Si) ₆ Sn ₆ displays a new framework motif for molecular tin compounds, in which six Sn atoms are located at the corners of a trigonal prism. The compound can be synthesized according to Equation (a). R*=SitBu₃.