Showing papers by "George M. Sheldrick published in 1990"
TL;DR: In this article, a phase annealing method, related to the simulated-annealing approach in other optimization problems, is proposed and it is shown that it can result in an improvement of up to an order of magnitude in the chances of solving large structures at atomic resolution.
Abstract: A number of extensions to the multisolution approach to the crystallographic phase problem are discussed in which the negative quartet relations play an important role. A phase annealing method, related to the simulated annealing approach in other optimization problems, is proposed and it is shown that it can result in an improvement of up to an order of magnitude in the chances of solving large structures at atomic resolution. The ideas presented here are incorporated in the program system SHELX-90; the philosophical and mathematical background to the direct-methods part (SHELXS) of this system is described.
14,787 citations
TL;DR: In this paper, the new compounds Se[N(SiMe 3 ) 2 ] 2 and Te[NMe 3 ] 2 were prepared in relatively good yields and their crystal structures determined by X-ray crystallography at low temperature.
Abstract: The new compounds Se[N(SiMe 3 ) 2 ] 2 and Te[N(SiMe 3 ) 2 ] 2 have been prepared in relatively good yields and their crystal structures determined by X-ray crystallography at low temperature. The Se compound crystallizes in the monoclinic system, space group C2/c. The Te compound crystallizes in the triclinic system, space group P1
69 citations
TL;DR: A cage‐like model consisting of a tetrameric c‐(GpGp) aggregate in which a large cavity is generated to afford a binding site for certain planar intercalators (‘guests’) is proposed.
44 citations
TL;DR: In this article, N,N′-Dilithiobis(alkylamino)phenylboranes with tetrachlorides MCl4 (M = Ge, Sn, Ti, Zr) produce the 4,4′-spirobi(1,3-dialkyl-2-phenyl-1, 3-diaza-2,bora-4-metalla-cyclobutane) derivatives 1a, 1b, 2b, 3a, and 3b.
Abstract: N,N′-Dilithiobis(alkylamino)phenylboranes as Starting Materials for Four-Membered Metallacycles
Reactions of N,N′-Dilithiobis(alkylamino)phenylboranes with tetrachlorides MCl4 (M = Ge, Sn, Ti, Zr) produce the 4,4′-spirobi(1,3-dialkyl-2-phenyl-1,3-diaza-2-bora-4-metalla-cyclobutane) derivatives 1a, 1b, 2b, 3a, and 3b. With diorganylmetal dihalides R2MX2(M = Sn, Zr; X = Cl, Br), the 1,3-diaza-2-bora-4-metallacyclobutanes 2a and 4 are obtained. For 3a an X-ray structure analysis has been performed.
40 citations
TL;DR: In this article, X-ray diffraction has been used to obtain hexane from PhB(NButLi)2 and PbCl4in hexane or from PbCL2 intetrahydrofuran.
Abstract: 1,3,5,7-Tetra-t-butyl-4,8-Biphenyl-1,3,5,7-tetra-aza-2,6-diplumba-4,8-diboratricyclo[4.2.0.02,5]octane-1,5-diium-2,6-diide(1)hasbeen obtained from PhB(NButLi)2 and PbCl4in hexane or from PbCl2 intetrahydrofuran and structurally characterised by X-ray diffraction.
22 citations
TL;DR: The first thione S-imides with perfluoromethyl groups were obtained by the use of Sodium Hexamethyldisilazanide as a Mild Dehydrohalogenation Reagent as discussed by the authors.
Abstract: Preparation of the First Thione S-Imides with Perfluoromethyl Groups by the Use of Sodium Hexamethyldisilazanide as a Mild Dehydrohalogenation Reagent
From the reaction of the sulfenyl chloride 1 with the monosilylated amines 2a, b the sulfenamides 3a, b are obtained in good yields. 1,3-Dehydrohalogenation of 3a, b with sodium hexamethyldisilazanide yields the thione S-imides 5a, b. Imide 5a reacts with norbornene (6) to produce the isothiazolidine derivative 7. The structures of 5b and 7 are confirmed by X-ray analyses.
19 citations
TL;DR: In this article, the structure of the free methanide SPPh2PCHPPh2Me has been established by X-ray crystallography [space group P21/c, with a= 15.392(4), b= 12.643(5), c= 21.965(7)A, β= 107.95(2)°, and R′= 0.224 A.
Abstract: Both [Au(C6F5)3(SPh2PCHPPh2Me)]{obtained from [Au(C6F5)3(OEt2)] and [SPh2PCH2PPh2Me]ClO4, followed by deprotonation with NaH} and the free methanide SPPh2CHPPh2Me react with gold(I) or silver(I) complexes [Au(C6F5)(tht)](tht = tetrahydrothiophene), [Au(tht)2]ClO4, and [Ag(OClO3)(PPh3)] to afford binuclear complexes of the types [Au(C6F5){SPh2 PCH[Au(C6F5)]PPh2Me}] or [{M(SPh2PCHPPh2Me)}2][ClO4]2(M = Au or Ag). The silver complex can also be obtained by deprotonation of [{Ag(SPh2PCH2PPh2Me)}2][ClO4]2 with Na2CO3. Oxidative addition of chlorine to the gold derivative gives the binuclear gold(II) complex [{AuCl(SPh2PCHPPh2Me)}2]. The structure of [Au(C6F5){SPh2PCH[Au(C6F5)] PPh2Me}] has been established by X-ray crystallography [space group P21/c, with a= 15.392(4), b= 12.643(5), c= 21.965(7)A, β= 107.95(2)°, and R′= 0.072 for 3 166 unique observed reflections]. The molecule adopts a folded conformation with parallel, eclipsed C6F5 rings and a corresponding short Au ⋯ Au contact of 3.224 A.
17 citations
TL;DR: In this paper, the reactions of subvalent species generated by the reaction of dichloro(diisopropylamino)borane with sodium/potassium alloy with unsaturated aliphatic hydrocarbons, have yielded the following compounds: the 2,5-dihydroboroles I and II from 1, 3-dienes; the 1,3-Dihydrodiboretes III and IV from alkynes; and the 1-bis(biopropyl-boryl-2-trimethylsily
17 citations
16 citations
TL;DR: In this article, the crystal structures of the octamethylcyclotetrasilazane (OCTS) are compared with one another and the coordinatively bonded TH in the lithium compound 1 can be exchanged with the Lewis base TMEDA.
Abstract: Alkali Salts of Octamethylcyclotetrasilazane - Synthesis and Crystal Structures
Octamethylcyclotetrasilazane reacts with n-butyllithium or the elements sodium and potassium to give the alkali salt 1, 2, and 3. 1–3 crystallize as dimeric THF adducts. In the dimers two eight-membered rings are connected by a planar alkali metal-nitrogen four-membered ring. Lithium is tricoordinated in 1, sodium tetracoordinated in 2, and potassium penta- and hexacoordinated in 3. The crystal structures of the alkali salts are discussed and compared with one another. The coordinatively bonded TH in the lithium compound 1 can be exchanged with the Lewis base TMEDA. The crystal structure of 4 shows a higher symmetry than that of 1.
14 citations
TL;DR: In this article, the conformation of N-Benzylpyridinium Bromide was investigated by X-ray analysis and semi-empirical MO methods (MINDO/3, MNDO, AM1, PM3).
Abstract: Conformational Analysis of N-Benzylpyridinium Bromide: A Comparison of Crystal Structure Data with Results of Semiempirical Calculations (MINDO/3, MNDO, AM 1, and PM3)
The conformation of the title compound 1b is investigated by X-ray analysis and semiempirical MO methods (MINDO/3, MNDO, AM1, PM3). For the calculation of bond lengths and bond angles, AM1 and MINDO/3 are superior. Without complete calculation of the hypersurfaces of the variable D1, D2 and the relative energy (e. g. Figure 2), AM1 and MNDO can lead to false interpretations. Cuts through these surfaces (Figure 1) are calculated within moderate CPU time, Normally, these cuts are sufficient to characterize the conformational situation. The electronic influence of the phenyl group on the N1–C7 bond length of N-alkylpyridinium salts and on the dissociation energy ΔHz (eg. 2) is estimated. The comparison of the data of 1a and 1b reveals that this group causes an elongation of this bond by 2 pm and a decrease of the dissociation energy by 200 kJ/mol.
TL;DR: In this paper, the reaction of the dilithium compound with a fluorsilane in equivalent amounts, the bicyclic compounds 14 and 15 were obtained, showing that the nitrogen atoms of the Si3N-units have a pyramidal environment.
Abstract: Mono- und dilithiiertes Octamethylcyclotetrasilazan (1, 6) reagieren mit Fluorsilanen bzw. F2BN(SiMe3)2 unter Erhalt des Cyclotetrasilazangerustes zu den mono- und disubstituierten Verbindungen 2–5 und 7–13. Bei der Umsetzung des Dilithiumsalzes (6) mit einem Fluorsilan im Molverhaltnis von 1:1 werden die Bicyclen 14 und 15 erhalten. Kristallographische Untersuchungen von 2, 3, 8 und 9 zeigen, das der monosilylierte Achtring in einer Wannen-, der disilylierte Achtring in einer Sesselkonformation vorliegt. In der Kristallstruktur des Bicyclus 14 zeigen die Stickstoffatome der Si3N-Einheiten eine pyramidale Umgebung.
Fluorosilyl and Fluoroboryl Substituted Cyclotetrasilazanes. Synthesis and Crystal Structures
Mono- and dilithiated octamethylcyclotetrasilazanes (1, 6) react with fluorosilanes and F2BN(SiMe3)2, respectively, under retention of the cyclotetrasilazane structure yielding the mono- and disubstituted compounds 2–5 and 7–13. In the reaction of the dilithium compound 6 with a fluorsilane in equivalent amounts, the bicyclic compounds 14 and 15 are obtained. Crystallographic investigations of the compounds 2, 3, 8, and 9 indicate that the monosilylated eight-membered ring has a cradle conformation while the disilylated ring has a chair conformation. The X-ray structure of the bicyclic system 14 indicates that the nitrogen atoms of the Si3N-units have a pyramidal environment.
TL;DR: In this article, the reactions of Cl3 with Ph3SiOH and ButOH lead not to the expected substitution products but to exchange and rearrangement reactions in which the nitrogen atoms which co-ordinate molybdenum are replaced by oxygen.
Abstract: The reactions of [[graphic omitted])Cl3] with Ph3SiOH and ButOH lead not to the expected substitution products but to exchange and rearrangement reactions in which the nitrogen atoms which co-ordinate molybdenum are replaced by oxygen. The crystal structures of [[graphic omitted])O2Cl2], [[graphic omitted])2(O)Cl], and [graphic omitted])2O2] are reported, together with the synthesis of these unexpected products by more direct routes.
TL;DR: In this article, the reaction of benzene with sodium/potassium alloy and dichloro(di-isopropylamino)borane (1 : 2) in 1,2-dimethoxyethane gives, in addition to other products, the title compound, characterised by its mass (El, Fl) and NMR (1H, 11B, 13C) spectra and X-ray crystallography.
Abstract: Reaction of benzene with sodium/potassium alloy and dichloro(di-isopropylamino)borane (1 : 2) in 1,2-dimethoxyethane gives, in addition to other products, the title compound, characterised by its mass (El, Fl) and NMR (1H, 11B, 13C) spectra and X-ray crystallography.
TL;DR: In this article, 1,3,5,7-cyclooctatetraene with sodium-potassium alloy and dihalogeno(diisopropylamino) boranes in 1,2-dimethoxyethane gives the title compound, characterized by elemental analysis, MS(EI, FI), NMR( 1 H, 11 B, 13 C), and X-ray crystallography
Abstract: The reaction of 1,3,5,7-cyclooctatetraene with sodium-potassium alloy and dihalogeno(diisopropylamino) boranes in 1,2-dimethoxyethane gives the title compound, characterized by elemental analysis, MS(EI, FI), NMR( 1 H, 11 B, 13 C), and X-ray crystallography
TL;DR: In this paper, 1,2,3-Tris(diiso propylamino)triborane was characterized by elemental analyses, spectroscopic data, and by an X-ray structure analysis.
Abstract: (3α,4β,4aβ,7aβ,8β,8aα)-1,2,3-Tris(diisopropylamino)-1,2,3,3a,44a,5,7a,8,8a-decahydro-4,8-methanoindeno[5,6-d]-1,2,3-triborol (1) is formed from dicyclopentadiene and dichloro(diisopropylamino)borane upon treatment with sodium/potassium alloy in hexane. 1,2,3-Tris(diiso propylamino)triborane(5) (2) was also obtained. 1 is characterized by elemental analyses, spectroscopic data, and by an X-ray structure analysis, 2 by its MS and NMR data.
TL;DR: In this article, the reaction of the mono-and dilithium derivatives of bis(fluorsilyl)-substituted cyclotetrasilazanes with fluorosilanes and fluoroboranes leads to ring contraction.
Abstract: Ring Contractions of Octamethylcyclotetrasilazanes to Silyl-Substituted Cyclotrisilazanes
Reaction of the mono- and dilithium derivatives of bis(fluorsilyl)-substituted cyclotetrasilazanes with fluorosilanes and fluoroboranes leads to ring contraction with formation of cyclotrisilazanes (1 – 8). The isomerisation is proved by the crystal structure determination of 1 and by NMR spectroscopy.
TL;DR: The S2N2 part of the five-membered ring may be described as a 6-π electron system as discussed by the authors, which was obtained by recrystallization from liquid SO2.
Abstract: Adduct of a Five-Membered Trisulfurdinitrogen Dioxide Ring with Titanium Tetrachloride
Reaction of S6N4O4 with TiCl4 lead to [(S3N2O2)TiCl4]2 (2). Single crystals of 2 were obtained by recrystallization from liquid SO2. 2 forms chains of five-membered S3N2O2 rings connected by Ti2Cl8 units. The S2N2 part of the five-membered ring may be described as a 6-π electron system.
TL;DR: In this paper, the cycle oxazepine adopte une conformation pseudo-bateau, which forme une liaison hydrogene faible de 2,84 A.
Abstract: C 25 H 27 NO 4 •H 2 O cristallise dans P2 1 avec a=6,563, b=7,922 et c=20,877 A, β=94,32 o , Z=2; affinement jusqu'a R=0,057. Determination des configurations relatives S et R en C(7a) et C(13b). Le cycle oxazepine≃7 membres adopte une conformation pseudo-bateau. Les deux dihydropyranne ont une conformation demi-chaise. Le compose du titre cocristallise avec une molecule d'eau qui forme une liaison hydrogene faible de 2,84 A
TL;DR: In this article, X-ray diffraction has been used to obtain hexane from PhB(NButLi)2 and PbCl4in hexane or from PbCL2 intetrahydrofuran.
Abstract: 1,3,5,7-Tetra-t-butyl-4,8-Biphenyl-1,3,5,7-tetra-aza-2,6-diplumba-4,8-diboratricyclo[4.2.0.02,5]octane-1,5-diium-2,6-diide(1)hasbeen obtained from PhB(NButLi)2 and PbCl4in hexane or from PbCl2 intetrahydrofuran and structurally characterised by X-ray diffraction.
TL;DR: In this paper, 1,2,3-Tris(diiso propylamino)triborane was characterized by elemental analyses, spectroscopic data, and by an X-ray structure analysis.
Abstract: (3α,4β,4aβ,7aβ,8β,8aα)-1,2,3-Tris(diisopropylamino)-1,2,3,3a,44a,5,7a,8,8a-decahydro-4,8-methanoindeno[5,6-d]-1,2,3-triborol (1) is formed from dicyclopentadiene and dichloro(diisopropylamino)borane upon treatment with sodium/potassium alloy in hexane. 1,2,3-Tris(diiso propylamino)triborane(5) (2) was also obtained. 1 is characterized by elemental analyses, spectroscopic data, and by an X-ray structure analysis, 2 by its MS and NMR data.
TL;DR: In this article, the cycle oxazepine adopte une conformation pseudo-bateau, which forme une liaison hydrogene faible de 2,84 A.
Abstract: C 25 H 27 NO 4 •H 2 O cristallise dans P2 1 avec a=6,563, b=7,922 et c=20,877 A, β=94,32 o , Z=2; affinement jusqu'a R=0,057. Determination des configurations relatives S et R en C(7a) et C(13b). Le cycle oxazepine≃7 membres adopte une conformation pseudo-bateau. Les deux dihydropyranne ont une conformation demi-chaise. Le compose du titre cocristallise avec une molecule d'eau qui forme une liaison hydrogene faible de 2,84 A
TL;DR: In this paper, the titanadiazaphosphetidines Ph2P[µ-N(SiMe3)]2TiCl3MeCN (1) and NPPh2N(NiMe3)2]-NSiCl2 (2) were shown to be monoclinic and triclinic, space group P21/n, respectively.
Abstract: Depending on the reaction conditions, Ph2P(NSiMe3)[N(SiMe3)2]reacts with TiCl4 to form the titanadiazaphosphetidines Ph2P[µ-N(SiMe3)]2TiCl3MeCN (1) and Ph2P[µ-N(SiMe3)]2TiCl2,[NPPh2N(SiMe3)2](2). Compound (1) dimerises slowly in solution with elimination of Me3SiCl to yield a tricyclic system containing a central Ti2N2 ring (3). X-Ray analyses of these compounds show (1) and (3) to be monoclinic, space group P21/n, while (2) is triclinic, space group P. Compound (2) has a Ti–N–P angle of 170.3(7)° and a short exocyclic Ti–N bond of 179.2(9) pm.