AbstractDie HF‐Eliminierung aus Fluorbis(amino)boranen des Typs R′ (Me3Si)NBFNHR (R = 2,6‐)Me2CH)2C6H3, R′ = Me (Ia), CH2Me (Ib), CHMe2 (Ic), CMe3 (Id), SiMe3 (Ie), R (If)) mit t‐Butyllithium im Molverhältnis 1:1 führt zu den Amino‐imino‐boranen (IIa–f), die – abhängig von der Größe des Substituenten R′ – unterschiedliche thermische Stabilität aufweisen. IIa – c und IIe dimerisieren zu den Diazadiboretidinen IIIa – c und IIIe. IId ist bis über 200°C stabil, während sich IIf bei dem Versuch seiner Isolierung zum Bor‐Methyl‐substituierten Diazasila‐boretidin IVf umlagert. Führt man die gleiche Umsetzung mit t‐Butyllithium im überschuß (Molverhältnis 1:2) durch, erhält man fast ausschließlich die Bor‐t‐Butyl‐substituierten Diaza‐sila‐boretidine Va – Vf.Alle Verbindungen sind elementaranalytisch (C, H) und spektroskopisch MS, NMR (1H, 13C, 15N (teilweise), 19F, 29Si) charakterisiert. Charakteristische IR‐Banden werden für die Amino‐imino‐borane (II) angegeben. Eine Röntgenstruktur‐analyse wurde von IVf angefertigt.

The crystal structures of three quinoxaline antibiotics-echinomycin 2QN, triostin C and the C222(1) form of triostin A--have been determined, and the structure of the P2(1)2(1)2(1) form of triostin A has been re-refined against our previously reported data. The molecular conformations are compared with those deduced from NMR data and those reported for two complexes of triostin A with oligonucleotides. Although the depsipeptide ring conformations are basically similar, the effective twofold molecular symmetry is violated by the folding of one of the quinoxaline chromophores in echinomycin 2QN and by a rotation of one of the ester planes with the formation of an intramolecular hydrogen bond in triostin C. In the oligonucleotide complexes of triostin A the chirality of the disulfide bridge is inverted. The alanine NH groups are involved in intermolecular hydrogen bonds in all four structures, and (except in echinomycin 2QN) the stacking of the chromophores in the crystal emulates the intercalation involved in DNA complex formation. In echinomycin 2QN, the antibiotic molecules are hydrogen bonded to form a helix along the crystallographic 6(5) screw axes, with a channel of disordered solvent running through the middle of the helix. Crystal data: (1), echinomycin 2QN, C53H66N10O12S2.2.5(C3H6O).2.5(H2O), M(r) = 1289.5, hexagonal, P6(5), a = b = 22.196(15), c = 24.64 (2) A, V = 10,513 (13) A3, Z = 6, Dx = 1.222 Mg m-3, lambda (Cu K alpha) = 1.5418 A, mu = 1.275 mm-1, T = 193 K, R = 9.0% for 4828 I > 2 sigma (I) and 11.8% for all 7102 unique reflections; (2), triostin C, C54H70N12O12S2.0.67(CHCl3).0.67(H2O), M(r) = 1234.2, orthorhombic, P2(1)2(1)2(1), a = 16.054 (8), b = 17.128 (9), c = 22.706 (12) A, V = 6244 (6) A3, Z = 4, Dx = 1.313 Mg m-3, lambda (Mo K alpha) = 0.71073 A, mu = 0.239 mm-1, T = 188 K, R = 7.7% for 4678 I > 2 sigma (I) and 14.0% for all 7260 unique reflections; (3), triostin A, C50H62N12O12S2.2(C7H14O2), M(r) = 1347.6, orthorhombic, P2(1)2(1)2(1), a = 20.94 (2), b = 18.53 (2), c = 18.80 (2) A, V = 7292 (13) A3, Z = 4, Dx = 1.228 Mg m-3, lambda (Cu K alpha) = 1.5418 A, mu = 1.245 mm-1, T = 293 K, R = 6.8% for 2116 I > 2 sigma (I) and 9.3% for all 2928 unique reflections; (4), triostin A, C50H62N12O12S2.HCl.2(C3H7NO), M(r) = 1269.9, monoclinic, C222(1), a = 10.622 (10), b = 17.035 (17), c = 35.21 (3) A, V = 6371 (10) A3, Z = 4, Dx = 1.324 Mg m-3, lambda (Mo K alpha) = 0.71073 A, mu = 0.199 mm-1, T = 153 K, R = 7.5% for 2164 I > 2 sigma (I) and 13.2% for all 3402 unique reflections. Extensive use was made of restraints on the geometrical and displacement parameters in the successful anisotropic refinement of these structures against weak data.

Octreotide, a synthetic somatostatin analogue, is an octapeptide with one disulfide bridge. Crystals of octreotide are orthorhombic, space group P2(1)2(1)2(1), a = 18.458 (5), b = 30.009 (7), c = 39.705 (27) A, with three molecules of octapeptide, one ordered oxalate dianion and 52 water molecules in the asymmetric unit. Complete protonation of the NH(2) groups (as assumed in the refinement) would require three oxalate dianions in the asymmetric unit for charge neutrality; a chemical analysis indicated that four are present. In either case they are so disordered that they cannot be distinguished from the water molecules. The 18 951 unique reflections (R(sym) = 0.026) used for structure solution and refinement were recorded with the EMBL imaging-plate scanner using synchrotron radiation. The structure was solved by Patterson interpretation, locating the three disulfide bridges, followed by tangent phase expansion and E-Fourier recycling. The anisotropic refinement against all F(2) data between 1.04 and 10.0 A resolution by blocked restrained full-matrix least-squares techniques converged to a conventional R index based on F of 0.084 [I > 2a(I) and 10.0 > d > 1.04 A] and wR2, the weighted R-index on F(2), of 0.246 (for all data). One peptide molecule adopts a flat beta-sheet structure; the other two possess different irregular backbone conformations, but are similar to each other. All three molecules have a distorted type II' beta-turn around the D-Trp-Lys region, but exhibit different side-chain conformations. The crystal structure is stabilized by a network of inter- and intramolecular hydrogen bonds.

The octapeptide octreotide crystallizes with three peptide molecules and about 20% water in the asymmetric unit, and in many ways possesses diffraction properties similar to those of a 'mini-protein' consisting of 24 amino-acid residues. It diffracts to about 1.0 A but data in the range 1.4-1.0 A are weak. It provides a suitable test of different macromolecular X-ray data-collection techniques, especially of their ability to measure weak reflections accurately. In contrast to typical proteins it is possible to perform a full anisotropic refinement, that we believe provides a more objective test of the quality of the data than the internal consistency of equivalent reflections. We have collected a total of six data sets. The X-ray sources included synchrotron radiation, Cu Kalpha rotating anodes and Mo Kalpha sealed tubes; position-sensitive two-dimensional detectors from four manufacturers and a four-circle diffractometer with scintillation counter were employed. Two of the six data sets were collected at low temperature. Reasonable anisotropic refinement was possible with all area-detector data sets, although significant differences in the precision of the final model were observed. In addition we tested the ability of automated Patterson interpretation to solve the structure using the six independent data sets. The structure solution was only successful using the synchrotron or rotating-anode data sets, i.e. for the more intense sources. It appears that for structure solution the maximum resolution of the data is critical, whereas for refinement the accuracy of the data is more important.

Acylic silylated phosphazenes of the type HN(PR 2 NSiMe 3 ), (1) react quantitatively with molecules MMe 3 (M=Al, Ga, In) under ring formation and CH 4 evolution. The ring compounds N(PPh 2 NSiMe 3 ) 2 AlMe 2 (2 a) and N(PPh 2 NSiMe 3 ) 2 InMe 2 (4 a) have been investigated by X-ray structure determination. 2a and 4 a crystallize in the space groups P1 and P3 1 , respectively; they show different conformations regarding the cyclohexane framework. NMR spectroscopy of the nuclei in the chelating phosphazene ligand indicates decreasing Lewis acidity of the metal containing fragments in the series AlMe 2 ≥GaMe 2 >InMe 2

Acylic silylated phosphazenes of the type HN(PR(2)NSiMe(3))(2) (1) react quantitatively with molecules MMe(3) (M = Al, Ga, In) under ring formation and CH4 evolution. The ring compounds N(PPh(2)NSiMe(3))(2)AlMe(2) (2a) and N(PPh(2)NSiMe(3))(2)InMe(2) (4a) have been investigated by X-ray structure determination. 2a and 4a crystallize in the space groups P $$($) over bar 1 and P3(1), respectively; they show different conformations regarding the cyclohexane framework. NMR spectroscopy of the nuclei in the chelating phosphazene ligand indicates decreasing Lewis acidity of the metal containing fragments in the series AlMe(2) greater than or equal to GaMe(2) > InMe(2).

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Reactions of vinyltrimethylsilane, propene, 3,3-dimethyl-1-butene, 1-butene, 3-methyl-1-butene, 1-pentene, 4,4-dimethyl-1-pentene, cyclopentene, cyclohexene and cyclooctene with dichloro(diisopropylamino)borane and Na/K-alloy in n-hexane yield the 1,2-diboretanes I-VII, IX, XI and the 1,2,3-triborolanes VIII, X, XII. By-products XIV and XVI–XVIII were found in the mass-spectra. In reaction to VII the 1,2,3,4-tetrakis(diisopropylamino)tetraborane(6) (XIX) was isolated as by-product. Vinyl-3-cyclohexene reacts under the same conditions to give the triborolane (XIII). The compounds I–XIII, XV and XIX were characterized by elemental analyses and spectroscopic data (MS; NMR: 1H, 13C, 11B, 29Si), X, XII, XIII and XIX also by X-ray structure analyses.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The reaction of (Me3Si)3SiLi (1) with acetone has been clarified with the aid of crystal structure and Si-29 NMR investigations of H(Me3Si)2Si-(Me3Si)2Si-CMe2SiMe3 (3) and (Me3Si)3Si-(Me3Si)2Si-CMe2SiMe3 (4). The chemically but not crystallographically equivalent silicon atoms in 3 and 4 and the two crystallographically independent molecules of 4 all gave rise to separate signals in the solid state Si-29-MAS NMR spectra. The 1J(Si-29, Si-29) couplings observed in solution facilitated the assignment of Si-29 resonances.

The crystal structures of (Me3Si)4Si.THF (a = b = 12.310(1) angstrom, c = 17.308(2) angstrom, tetragonal, space group P4/ncc (No. 130), Z = 4), [(Me3Si)4Si] [(Me3Si)3SiLi(THF)3]2 (a = b = 15.146(8) angstrom, c = 21.338(10) angstrom, trigonal, space group P3clBAR (No. 165), Z = 2), (Me3Si)3SiLi(THF)3 (a = b = 31.342(4) angstrom, c = 22.000(6) angstrom, rhombohedral, space group R3c (No. 161), Z = 24), and (Me3Si)3SiSi(SiMe3)3.THF (a = 11.360(3) angstrom, b = 17.131(6) angstrom, c = 18.952(6) angstrom, beta = 91.21(3)-degrees, monoclinic, space group P2(1)/c (No. 14), Z = 4), have been determined by low-temperature X-ray analysis. Whereas the small Si-Si-Si angle in (tris(trimethylsilyl)silyl)lithium of 102.1-degrees supports the ionic character of the Si-Li bond, there must be at least some covalent contribution leading to a (1J[Si,Li])-Si-29-Li-7 coupling constant of 38.6 Hz. A modified preparation for (Me3Si)3SiLi(THF)3 is reported giving the pure product rather than the cocrystallization product [(Me3Si)4Si] [(Me3Si)3SiLi(THF)3]2, Where the starting material is still present in the ratio 1:2. The pure product is far more reactive than the cocrystallized material and is as pyrophoric as (t)BuLi powder.

A SiCu2 three-center two-electron bond with(~)short Cu-Cu distance is the prominent structural feature of the lithium silylcuprate Li(thf)4-1 mentioned in the title compound, the first compound of this type characterized by X-ray crystallography (in the picture the SiMe, substituents have been omitted). The structure of the aluminate corresponds to a frozen intermediate from the reaction of (Me3Si)3SiLi and AlCl3. The two compounds are only stable at low temperatures.(~)[GRAPHICS]

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The synthesis and crystal structure of 1,3-di-tert-butyl-4,4-dimethyl-2-pentafluorophenyl-1,3,4,2-diazastannoboracyclobutane are reported.

2,5-Bisdimethylamino-2,5-dihydrobenzo[b]-1,2,5-thiadiborole(2) has been obtained from the diiodine-derivative by reaction with dimethyl-aminotrimethylsilane. Reaction of 2 or 2,5-bisdimethylamino-1',2'-dimethyl-2,5-dihydrobenzo[b]-thiadiborole with di-tert-butyl-, tert-butyl-trimethylsilyl- and bistrimethylsilyl-sulfurdiimide yields the 2,7,3,6-tetrahydrobenzo[b]-1,2,7,3,6-thiadiazadiborepines

A central kite-shaped AlH2Li ring in which the Li atom bridges the two hydride ligands bound to the Al atom is found in an intermediate of the reaction of HN(SiMe3)2 with LiAlH4. The bond angles show that compound 1 is relatively strained. Nevertheless, 1 does not dissociate in solution; in the (LiNMR)-Li-7 spectrum at low temperature a 1J(Li,H) coupling is observed. [(Me3Si)2N]2AlH2Li . 2 Et2O 1.

Amino-iminoboranes R'(SiMe3)N-B = N-R: IIc (R' = CHMe2), IId (R' = CMe3) and IIe (R' = SiMe3) carrying the supermesityl group (R) on the imino nitrogen atoms have been prepared from the corresponding fluorobis(amino)boranes Ic-e by HF-elimination using t-BuLi (IIc, d) or N-lithio-bis(trimethylsilyl)amid (IIe). The Amino-iminoboranes are thermally stable at room temperature. Upon treatment of the fluorobis (amino)boranes Ia, Ib, Ie with t-BuLi, LiF and HN(SiMe3)R' are eliminated and the B-t-butyl substituted iminoborane III is formed. The compounds are characterized by elementary analyses and spectroscopic data (MS, IR, NMR). An X-ray diffraction study has been performed for Ild.

2,5-Bisdimethylamino-2,5-dihydrobenzo[b]-1,2,5-thiadiborole (2) has been obtained from the diiodine-derivative by reaction with dimethyl-aminotrimethylsilane. Reaction of 2 or 2,5-bisdimethylamino-1',2'-dimethyl-2,5-dihydrobenzo[b]-thiadiborole with di-tert-butyl-, tert-butyl-trimethylsilyl- and bistrimethylsilyl-sulfurdiimide yields the 2,7,3,6-tetrahydrobenzo[b]-1,2,7,3,6-thiadiazadiborepines (3a-3e). H-1, B-11, C-13 NMR, MS and analytical data and results of analysis are given. For 3a the X-ray structure is reported.