Gertraud Geiseler

Two-electron aromatics containing three and four adjacent boron atoms

A two-electron aromatic bis (tris-trimethylsilylmethylene)-substituted tetraborane(4) was found to be a useful precursor for the synthesis of two-electron aromatic tetraboranes(6), triboracyclopropanates,as well as tetraboranes(6) distorted toward triboracyclopropanates with boryl bridges. Bishomo two-electron aromatics with a borata bridge and a protonated borata bridge, respectively, are also presented.

A Five-Membered Ring with Three Negative Charges and Solvent-Free Lithium Counterions

Remarkably short distances to the ring plane are shown by the eta(5)-bound lithium ions in the first compound with a triply negatively charged five-membered ring, 1, which was obtained by reduction of 2 with lithium. R=CH(SiMe(3))(2), Dur=2,3,5,6-tetramethylphenyl.

Reaktionen von LiNPPh3 mit den Cyclooctatetraenid-Komplexen [Ln(C8H8)Cl(THF)2]2 von Cer und Samarium. Die Kristallstrukturen von [LiNPPh3]6, [Ln(C8H8)Li3Cl2(NPPh3)2(THF)3] (Ln = Ce, Sm) und [Li(THF)4][Sm(C8H8)2]

LiNPPh3 reagiert mit den Cyclooctatetraenid-Komplexen [Ln(C8H8)Cl(THF)2]2 von Cer und Samarium in THF-Losung unter Bildung der Phosphaniminato-Komplexe [Ln(C8H8)Li3Cl2(NPPh3)2(THF)3], in denen nach Kristallstrukturanalysen Heterocuban-Strukturen unter Beteiligung des Lanthanoid-Metallatoms, der drei Li-Atome sowie der beiden Cl- und der beiden N-Atome der NPPh3–-Gruppen vorliegen. Die Kristallstruktur von LiNPPh3 zeigt hexamere Molekule mit einem Li6N6-Polyeder, das peripher durch die Phenylgruppen abgeschirmt ist. Die Struktur des als Nebenprodukt isolierten [Li(THF)4][Sm(C8H8)2] enthalt das Samarium-Atom in sandwichartiger Koordination durch die beiden η8-C8H82–-Ringe, wie es auch von den entsprechenden Anionen mit Cer und Neodym bekannt ist. Reactions of LiNPPh3 with the Cyclooctatetraenide Complexes [Ln(C8H8)Cl(THF)2]2 of Cerium and Samarium. Crystal Structures of [LiNPPh3]6, [Ln(C8H8)Li3Cl2(NPPh3)2(THF)3] (Ln = Ce, Sm) and [Li(THF)4][Sm(C8H8)2] LiNPPh3 reacts with the cyclooctatetraenide complexes [Ln(C8H8)Cl(THF)2]2 of cerium and samarium in tetrahydrofuran solution forming the phosphorane iminato complexes [Ln(C8H8)Li3Cl2(NPPh3)2(THF)3]. According to crystal structure analyses these complexes show heterocubane structures under participation of the lanthanoid metal atom, of the three Li atoms as well as of the two Cl und the two N atoms of the NPPh3– groups. The crystal structure of LiNPPh3 shows hexameric molecules with a Li6N6 polyhedron which is peripherally shielded by the phenyl groups. The structure of [Li(THF)4][Sm(C8H8)2], which has been isolated as a by-product, contains the samarium atom in a sandwichlike coordination by the two η8-C8H82– rings as it is also known from the corresponding anions with cerium and neodymium.

[In3Br3{C(SiMe3)3}3][Li(THF)3] mit einer Kette aus drei Indiumatomen — ein bemerkenswertes Nebenprodukt aus der Synthese des Tetraindiumclusters In4[C(SiMe3)3]4

Durch Umsetzung von Indiummonobromid mit dem Tetrahydrofuran-Addukt der Lithiumverbindung LiC(SiMe3)3 gelingt die einfache Synthese der tief violetten Tetraindiumverbindung In4[C(SiMe3)3]4 (1), die uber einen tetraedrischen Cluster aus vier einwertigen Indiumatomen verfugt. Dabei entsteht in grosen gelben Kristallen als Nebenprodukt [In3Br3{C(SiMe3)3}3]— [Li(THF)3]+ (2), dessen Konstitution wir jetzt aufklarten. 2 bildet eine Kette aus drei durch InIn-Einfachbindungen miteinander verbundenen Indiumatomen, von denen die beiden terminal angeordneten durch zwei Bromatome verbruckt werden. Das mittlere Indiumatom bindet an ein Bromidion, das eine Bruckenposition zum Gegenion [Li(THF)3]+ einnimmt. [In3Br3{C(SiMe3)3}3][Li(THF)3] with a Chain of Three Indium Atoms — a Remarkable By-product of the Synthesis of the Tetraindium Cluster In4[C(SiMe3)3]4 The reaction of indium bromide InBr with the THF adduct of LiC(SiMe3)3 afforded the deep violet tetraindium compound In4[C(SiMe3)3]4 (1) which possesses a tetrahedral cluster of four monovalent indium atoms. A yellow by-product was isolated and identified now as the compound [In3Br3{C(SiMe3)3}3]— [Li(THF)3]+ (2). 2 has a chain of three indium atoms connected by In-In single bonds. The terminal indium atoms are bridged by two bromine atoms, and the inner indium atom is attached to a bromide ion which bridges the In3 chain and the counter ion [Li(THF)3]+.

Very strong anionic homoaromaticity in (deloc-1,3,4)-1-sila-3,4-diboracyclopentane-1-ides, the importance of the energy of the reference system for homoaromatic stabilization energies

( deloc -1,3,4)-1-Sila-3,4-diboracyclopentane-1-ide ( 3a ) was prepared as solvent separated ion pair [Li(Et 2 O)(thf) 3 ][ 3a ] and as contact ion pair [Li(Et 2 O)][ 3a ]. Both were fully characterized by NMR spectroscopy as well as by X-ray structure analyses. Their five-membered rings are strongly distorted as seen from short transannular Si⋯B distances of 206 and 208 pm as compared with 276 pm in the undistorted 1-sila-3,4-diboracyclopentane ( 4c ). This distortion is also found in the unsubstituted prototype 3u by geometry optimizations at the MP2/6-311+G** level of theory. In addition, computations show that a three-center-two-electron (3c2e) bond between the silicon and the two boron atoms is present in the distorted 3u . The planar classical reference molecule 3u * with a 2c2e π bond between the boron atoms is not accessible by computations. Therefore, the energy difference between 3u and 3u * was estimated by isodesmic equations to be about 80 kcal mol −1 (at MP4/6-311+G**), considerably larger than any homoaromatic stabilization energy (HSE) ever discussed. The origin of this huge HSE of 3u is strong electrostatic destabilization of the reference system 3u * due to intramolecular charge separation. The series of bishomoaromatic systems is thus extended by a borderline case of very large HSE. The very small HSE of 1u at the other end of the series is also due to the energy of the reference: 1u * is strongly stabilized by hyperconjugation.

Die Kristallstrukturen der Triarylzinkate [Mg2Br3(THF)6][ZnPh3] und [MgBr(THF)5][ZnMes3]

Crystal Structures of the Triarylzincates [Mg2Br3(THF)6][ZnPh3] and [MgBr(THF)5][ZnMes3] The title compounds were obtained from reactions of the phosphoraneiminato complex [ZnBr(NPMe3)]4 with excess Grignard reagents RMgBr (R = C6H5, 2,4,6-(CH3)3–C6H2) in THF solution. According to X-ray structure determinations the [ZnR3]– ions contain zinc atoms which are coordinated in a planar fashion with Zn–C distances of 200.7 pm (R = Ph) and 203.4 pm (R = Mes) in average.

Nonorthogonal Dilithium-1,3-biborataallenes Containing Planar-Tetracoordinate Carbon Atoms

Deviations of up to 36° from the orthogonality of the planes of the terminal B atoms of the allene skeleton and their neighbors (ipso-C atoms) are observed in tetraaryl-1,3-diborataallenes of contact-ion triples 1. The unusual geometries are caused by steric hindrance between ortho-methyl groups, which is induced by interactions of the lithium counterions with the π electrons of the aryl substituents, as well as by small barriers to planarization of 1,3-diborataallenes. Ar=for example, 2,3,5,6-tetramethylphenyl.

DOMINO EFFECT IN THE BUILDUP OF N-I-N-I CHAINS OF THE N-IODINE(TRIPHENYLPHOSPHANE)IMINE

Up to the tetramer can be formed in a stepwise manner by an ionic domino mechanism by adding varying amounts of iodine to N-iodine(triphenylphosphane)imine, INPPh3, which does not exhibit intermolecular N⋅⋅⋅I contacts in the crystalline state. The tetramer [I(INPPh3)4]+I3− with alternatingly long N-I-N-I bonds (see picture) is possibly not the last member of this series of new N-I-N associates.

Unexpected formation of gallium–gallium single bonds by irradiation of the hydride [(Me3C)2GaH]3

Di(tert-butyl)gallium hydride 1 dismutates partially in solution forming tri(tert-butyl)gallium 2 and the sesquihydride [(Me3C)2GaH]2[H2GaCMe3]2 (3). The loss of tert-butyl radicals upon irradiation of this mixture with day light or an UV lamp gave the hexagallium compound (Me3CGaGaCMe3)2(μ-H)2[μ-H2Ga(CMe3)2]2 (4), which possesses two Ga–Ga single bonds. These Ga2 groups are bridged by two hydrogen atoms to give a six-membered Ga4H2 heterocycle. Couples of opposite gallium atoms of this heterocycle are bridged via Ga–H–Ga 3c–2e bonds by two H2Ga(CMe3)2 ligands, which are situated above and below the molecular plane. Compound 4 may be described as a hypho-hexagallane(14) cluster compound.

Donor-Akzeptor-Komplexe von Halogenidionen mit 1.4-Diiodtetrafluorbenzol/Donor-Acceptor Complexes of Halide Ions with 1,4-Diiodotetrafluorobenzene

(Ph4P)X as well as (Me4N)X (X = Cl, Br, I) react with 1,4-diiodotetrafluorobenzene in CH2C12 and CH3CN solutions, respectively, to give the donoracceptor complexes (Ph4PM (C6F4I2)Cl2]·4 CH2Cl2 (1), (Ph4P)2[(C6F4I2)Br2]·2 CH2Cl2 (2), (Me4N)[(C6F4I2)Cl] (3), (Me4N)[(C6F4I2)Br]·CH3CN (4), (Ph4P)2[(C6F4I2)3Br2]·4CH2Cl2 (5), (Ph4P)2[(C6F4I2)3I2] (6) and (Me4N)2[(C6F4I2)3I2] (7). All complexes have been characterized by single X-ray crystallographic structure determinations. 1: Space group P1̄, Z = 1, lattice dimensions at 203 K: a = 1090.2(1), b = 1206.2(1), c = 1242.8(1) pm, α = 91,84(1)°, β = 106.60(1)°, γ = 99.84(1)°. 2: Space group P1̄, Z = 1, lattice dimensions at 233 K: a = 1129.7(2), b = 1183.9(1), c = 1293.4(1) pm, α = 65.52(1)°, β = 65.74(1)°, γ = 89.02(1)°. 3: Space group P21/n, Z = 4, lattice dimensions at 243 K: a = 714.8(1), b = 2405.7(3), c = 930.8(1) pm, β = 96.38(1)°. 4: Space group P21/c, Z = 4, lattice dimensions at 203 K: a = 1400.8(1), b = 1669.9(2), c = 795.9(1) pm, β = 102.81(1)°. 5: Space group Pbca, Z = 4, lattice dimensions at 223 K: a = 2106.0(4), b = 1566.8(3), c = 2445.8(4) pm. 6 : Space group P1̄, Z = 1, lattice dimensions at 203 K: a = 1150.9(1), b = 1278.9(1), c = 1292.9(2) pm, α = 65.47(1)°, β = 82.07(1)°, γ = 83.62(1)°. 7: Space group Pbca, Z = 4, lattice dimensions at 223 K: a = 1210.5(5), b = 1429.0(6), c = 2470.3(12) pm. In all complexes the acceptor molecule C6F4I2 coordinates with the halide donor ions in linear arrangements C-I· · ·X- . In 1 and 2 the halide ions act as terminal donors to form the dianionic species [X· · ·I-C6F4-I· · ·X]2- (X = Cl, Br). Complexes 3 and 4 form polymeric anionic zigzag chains with μ-X- bridges and bond angles I· · ·Cl· · ·I of 77.2° and I· · ·Br· · ·I of 74.3°. Complexes 5 - 7 are characterized by three-dimensional anionic networks via /x3-X- bridging halide ions and μ-bridging 1,4-diiodotetrafluorobenzene molecules.