Martina Schäfer

Molecular Model for Aluminophosphates Containing Fluoride as a Structure‐Directing and Mineralizing Agent

Two tricyclic capped six-rings (C6R), a double four-ring (D4R), and an Al(μ-F)2 Al unit are among the structural features of 1 (see picture for structure) that are closely related to motifs found in layered and three-dimensional alumino- and gallophosphates. Several reactive centers can render 1 a viable precursor for the synthesis of microporous aluminophosphates.

Cyclooctatetraenyl-komplexe der frühen übergangsmetalle und lanthanoide: III. Cyclooctatetraenyl-lanthanoidtriflate und -iodide: Neue ausgangsmaterialien für die organolanthanoid-chemie

Abstract The dimeric complexes [(COT)Ln(μ-O 3 SCF 3 )(THF) 2 ] 2 (Ln  Ce ( 1 ), Pr ( 2 ), Nd ( 3 ), Sm ( 4 )) are easily prepared by treatment of anhydrous lanthanide(III) triflates with equimolar amounts of K 2 COT (COT = η 8 -cyclooctatetraenyl(2−)). The reaction of lanthanide triiodides with K 2 COT affords monomeric complexes of the type (COT)Ln(I)(THF) 3 (Ln  Nd ( 5 ), Sm ( 6 )). Due to their increased solubility in polar organic solvents these new precursors offer preparative advantages over the previously used chloro derivatives [(COT)Ln(μ-Cl)(THF) 2 ] 2 . The molecular structures of 3 and 5 have been determined by X-ray diffraction.

Crystal Structures of Actinomycin D and Actinomycin Z3

Untwinned single crystals of the actinomycins D and Z3 that diffracted to atomic resolution could be obtained for the first time. Low-temperature data collection and a new ab initio method for solving the structures led to precise crystal structures which showed, for example, that the unit cell of actinomycin D contains three molecules, two of which are present in the form of a hydrogen-bridged dimer related by a pseudo-twofold axis (see picture).

Facial-Selective Allylation of Methyl Ketones for the Asymmetric Synthesis ofα-Substituted Tertiary Homoallylic Ethers

The asymmetric synthesis of enantiomerically pure a-substituted tertiary homoallylic ethers 4a, 11 and 12a-c by the allylation of ethyl methyl ketone (la) with gamma-substituted allylsilanes 9a-h is described. The allylsilanes were obtained by a nickel-catalysed Grignard cross-coupling reaction of (E)- and (Z)-(3-iodoallyl)trimethylsilane with various Grignard reagents. The reaction of the allylsilanes with la in the presence of the trimethylsilyl ether of N-trifluoroacetylnorpseudoephedrine (3), and catalytic amounts of a mixture of trimethylsilyl triflate and trifluoromethanesulfonic acid led to the homoallylic ethers 4a, 11 and 12a-c with two new stereogenic centres, with a selectivity of 1:9 to >20:1 for the homoallylic and of 1:99 to >60:1 for the allylic centre. The facial selectivity does not depend on the configuration of the allylsilane, and in all reactions the anti product is preferentially formed. Interestingly, a pronounced switch of facial selectivity takes place with increasing length of the alkyl group of the allylsilane.

Structure of Balhimycin and its Complex with Solvent Molecules

Balhimycin is a naturally occurring glycopeptide antibiotic, related to vancomycin which acts by binding nascent bacterial cell-wall peptide ending in the sequence D-Ala-D-Ala. Crystals of balhimycin are monoclinic, space group P21, a = 20.48 (10), b = 43.93 (21), c = 27.76 (14) A, beta = 100.5 (5) degrees with four independent antibiotic molecules, three molecules of 2-methyl-2,4-pentanediol, two citrate ions, three acetate ions and 127.5 water molecules in the asymmetric unit. With an asymmetric unit larger than those of the smallest proteins and a solvent content of about 32%, the crystals have similar diffraction properties to those of small proteins. 27387 unique reflections were collected using synchrotron radiation. The structure was solved by a standard protein technique, the molecular-replacement method, using ureido-balhimycin as search model. The anisotropic refinement against all F2 data between 0.96 and 45 A converged to a conventional R value of 11.27% with R1= Sigma||Fo|-|Fc||/Sigma|Fo| for the 24623 data with I > 2sigma(I) and 12.58% for all 27387 data. The four monomers possess fairly similar conformations (r.m.s. deviation 0.7 A). Two antibiotic molecules form a tight dimer with antiparallel hydrogen bonds between the peptide backbone as well as between the vancosamine residues and the peptide backbone. In each of the two dimers, one binding pocket is occupied by a citrate ion and the other by an acetate ion. The dimer units are linked in the crystal by hydrogen bonds to form infinite chains.

Cyclooctatetraenyl-komplexe der frühen übergangsmetalle und lanthanoide: IV. Strukturchemie des anionisichen sandwich-komplexes [Ce(COT)2]−☆

Abstract The cerocene(III) derivatives [Li(THF) 4 ][Ce(COT) 2 ] ( 1 ) and (THF) 3 Na(μ-COT)Ce(COT) ( 2 ) have been prepared and characterized structurally by an X-ray diffraction study (COT  η 8 -cycloocta-tetraenyl(2−)). The molecular structures differ significantly, depending on the nature of the alkali metal cation. In the solid state, compound 1 consists of separated ion pairs. In 2 a cyclooctatetraenyl ligand bridges cerium and sodium to give a linear (COT)Ce(μ-COT)Na arrangement.

Neuartige Koordination eines cyclopentadienylrings im heterotrimetallischen organoyttrium-komplex Li[Cp2Y(FcN)2] (FcN = 2-dimethylaminomethylferrocenyl)

Abstract Treatment of bis(cyclopentadienyl)yttrium(III) chloride with two equivalents of 2-dimethylaminomethylferrocenyl lithium affords the novel heterotrimetallic complex Li[Cp 2 Y(FcN) 2 ] ( 1 ). A single-crystal X-ray structure determination of 1 reveals the presence of an unprecedented bonding mode of a cyclopentadienyl ring.

ANIONISCHE 1,2-(O N)- UND NEUTRALE 1,2-(N O, O N)-SILYLGRUPPEN-WANDERUNG: SYNTHESE ISOMERER TRIS(SILYL)HYDROXYLAMINE UND EINES SILYLAMINODISILOXANS

The lithium derivative of N , O -bis( tert -butyldimethylsilyl)hydroxylamine, Me 3 CSiMe 2 NHOSiMe 2 CMe 3 ( 1 ), is isolated as the first dimeric O -lithium- N , N -bis(silyl)hydroxylamide, [(THF)LiON(SiMe 2 CMe 3 ) 2 ] 2 ( 2 ). The tendency of the hard Lewis-acid lithium to bind the hard Lewis-base oxygen explains the O→N-silyl group migration. 2 reacts with tert -butyltrifluorosilane to give the tris(silyl)hydroxylamine Me 3 CSiF 2 ON(SiMe 2 CMe 3 ) 2 ( 3 ). An irreversible rearrangement involving positional exchange between the fluorosilicon group on oxygen and one organosilicon group on nitrogen in 3 leads to the formation of the isomeric tris(silyl)hydroxylamine Me 3 CSiMe 2 ON(SiMe 2 CMe 3 )SiF 2 CMe 3 ( 4 ). The rearrangement proceeds via a dyotropic transition state. 4 undergoes an intramolecular thermal rearrangement involving the insertion of a silyl moiety into the NO bond and the transfer of a methyl group from silicon to nitrogen. The silylaminodisiloxane Me 3 CSiMe 2 OSiMe(CMe 3 )NMeSiF 2 CMe 3 ( 5 ) is obtained. The influence of the effects of the substituents of the product formation is discussed and the crystal structure of 2 is reported.

Indolyl- und Pyrrolylsilane – Synthese und Kristallstruktur / Indolyl- and Pyrrolylsilanes – Syntheses and Crystal Structures

Lithium indolide and lithium pyrrolide react with fluoro- and chlorosilanes with formation of mono- and bis(indol-1-yl)- and -(pyrrol-1-yl)silanes, tris- and tetrakis(pyrrol-1-yl)silanes as well as of silanes substituted with different heteroaromatic systems. The crystal structures of the lithium indolide and the tetrakis(pyrrol-1-yl)silane have been determined and are discussed.

Cyclooctatetraenyl-komplexe der frühen Übergangsmetalle und lanthanoide: V. Synthese und struktur von monocyclooctatetraenyl-komplexen des dreiwertigen Titans

Abstract [(COT)Ti(μ-Cl)(THF)]2 (1) reacts with K[HBpz3] or K[HB(3,5-Me2pz)3] to give the new monocyclooctatetraenyl half-sandwich complexes (COT)Ti[HBpz3] (2) and (COT)Ti[HB(3,5-Me2pz)3] (3) respectively, as dark green, air-sensitive solids (COT  η8-cyclooctatetraenyl(2-)). The molecular structure of 2 has been determined by an X-ray diffraction study. The monomeric organotitanium(III) complexes (COT)Ti[PhC(NSiMe3) 2](THF) (4), (COT)Ti[MeOC6H4C(NSiMe3)2](THF) (5) and (COT)Ti[Ph2P (NSiMe3)2] (6) have been prepared by treatment of [(COT)Ti(μ-Cl)(THF)]2 (1) with the corresponding heteroallylic ligands.