bluuebunny/crossref_metadata_2025 huggingface dataset:
Silaheterocyclen, XXIII. Synthese und Thermolyseverhalten von Si‐funktionellen 2‐Silaazetidinen
Authors: Auner Norbert , Weingartner Armin W. , Bertrand Guy
Published: July 2007

Silaheterocycles, XXIII[1]. – Synthesis and Thermolysis Reactions of Si‐Functionalized 2‐Silaazetidines

Dichloroneopentylsilene (1) is formed in situ by the reaction of trichlorovinylsilane with LitBu. The [2 + 2] cycloaddition to imines yields Si, Si1‐dichloro‐functionalized 2‐silaazetidines in a preparative scale. With aldimines as trapping agents for 1, the resulting SiN four‐membered ring compounds are isolated as syn/anti1‐isomers (e.g. syn/anti‐15 and ‐16; syn/anti ≈︁ 2:1). Silene 1 is not liberated from the silaazetidines on heating, but the Si, Si1‐dichloro‐substituted silanimine Cl2SiNtBu (24) is formed. This can be trapped by Me3SiOMe or Ph2CNtBu to give the addition products 25 and 26, respectively. The pathways are discussed which lead to stereoisomeric SiN ring compounds by a multiple‐step mechanism including zwitterionic intermediates (1,4‐dipoles). In addition there is strong evidence for the formation of 1, depending on the trapping reagent used. This fact may be explained by donor→silene interactions. The thermolysis products of silaazetidines support the formulation of a stepwise decomposition to an alkene and Cl2SiNR derivatives.
Tetraaza‐λ31‐diphospha‐stanna‐bicyclo[3.1.1]heptane: reaktive Vorstufen neuer Heterobicyclen
Authors: Linti Gerald , Nöth Heinrich , Schneider Ellen , Storch Wolfgang
Published: July 2007

Tetraaza‐λ31‐diphospha‐stanna‐bicyclo[3.1.1]heptanes: Reactive Precursors of New Heterobicycles

2,4,6,7‐Tetraaza‐1λ3,5λ31‐diphospha‐3‐stannabicyclo[3.1.1]heptane (4) is obtained by stannazane cleavage of the diazadistannetidine (Me2SnNtBu)2 (2) with the diazadiphosphetidine (CIPNtBu)2 (1). A chloro derivative of 4, compound 8, is formed by substitution of one methyl group attached to the tin atom in 4 against chlorine in a 1:1 reaction with PhBCl2, while additional PhBCl2 leads to an exchange of the MeClSn against the PhB group to give 9. Oxidation of both phosphorus atoms of compound 4 with sulfur leads to 7. An unexpected introduction of a diphenyldiphosphane unit with formation of 11 proceeds by stannazane cleavage of 4 with PhPCl2. The structures of the bicyclic products 4, 7, 8, and 11 are ascertained by detailed NMR studies, particularly by means of 15N‐NMR spectra, and by X‐ray structure determinations. All heterobicycles contain a planar diazadiphosphetidine unit. The ring system 8 features an additional Sn – N bond due to transannular interaction of the tin atom with one of the nitrogen atoms of the four‐membered P2N2 ring fragment. The PP bond distance in 11 with 2.175 Å is one of the shortest found in heterocycles containing P2 units.
Metal‐Metal Bonding in Paramagnetic Chromium(III) Complexes – An MO‐Theoretical Case Study
Authors: Janiak Christoph , Silvestre Jérǒme , Theopold Klaus H.
Published: July 2007

The electronic structures of the edge‐sharing bioctahedral chromium(III) dimers {C5H5Cr(CH3)(μ1‐Cl)}2 (2) and {Me5C5Cr(CH3)(μ1‐CH3)}2 (4* (Cp* derivative), 4 (Cp derivative)), the trinuclear complex {C5H5Cr(μ1‐Cl)}3(μ1‐CH) (3), and the face‐sharing bioctahedral chromium(III) compounds {Me5C5Cr}2(μ1‐CH2) (6*, 6) [{Me5C5Cr}2(μ1‐CH3)3]+ (7*, 7) have been studied MO‐theoretically by the extended Hückel method. Proceeding from 2 over 3 to 4*, or from 6* to 7* a 3‐center/4‐electron chloride or methylene bridge is replaced by a 3‐center/2‐electron methyl group (a methylidyne cap in the trimer). The 3c/2e bridges give rise to an increased metal – metal overlap population due to Cr – Cr bonding within the core levels. In the series of 2 – 3 – 4* this is accompanied by a decrease in the Cr – Cr distance (329 – 284 – 260 pm) and effective magnetic moment, μeff (2.53 – 2.05 – 1.53 μB per Cr at room temp.). The latter can be ascribed to an increased splitting within the chromium d‐block because of the shorter metal‐metal separation. The bioctahedra 6* and 7* feature even shorter Cr – Cr contacts than 4* (239 and 242 pm), primarily because of their face‐sharing geometry. However, their effective magnetic moments (per Cr) are 2.33 and 1.32 μB at room temp. The high magnetic moment for 6* can be understood from the orbital interactions in the frontier orbital metal d block: A face‐sharing bioctahedron shows one σ, two δ, and no π type overlap, while an edge‐sharing bioctahedron (4) has σ, π, and δ interaction between the metals. In the former this destabilizes only σ* sufficiently to prevent occupation by electrons (leaving five orbitals for six electrons, possible spin multiplicities S0, 1, 2) while for the latter both σ* and π* are destabilized beyond electron occupation (leaving four MOs for six electrons, possible spin multiplicities S0, 1). 4*, 6* and 7* are unusual examples of metal – metal bonded complexes containing octahedral CrIII ions.
Synthese und Struktur von Phosphiren‐Iminen und Iminophosphaspiro[2.2]pentanen
Authors: Barion Detlef , David Gabriele , Link Manfred , Nieger Martin , Niecke Edgar
Published: July 2007

Synthesis and Structure of Phosphirene Imines and Iminophosphaspiro[2.2]pentanes

The reaction of the iminophosphanes R1PNR2[1, R22,4,6‐tBu3C6H2;R1Me (a) Et (b), PhCHCH (c), Cl (d); R2tBu, R1Et3C (e)] with the alkynes R3C  CR4 [2, R3R4Ph (a), CO2Me (b)] affords the corresponding phosphirene imines 3a – g. A [2 + 1] cycloadduct 3h is also formed in the reaction of the alkyne 2c (R3H, R4Ph) with 1d, while in the case of 1b the 1,2‐addition product 4 is obtained. As demonstrated by the [2 + 1] cycloaddition reaction of the P1‐alkylated iminophosphanes 1a, b with methylene‐cyclopropanes 5a, b, the formation of the iminophosphaspiro[2.2]pentanes 6a, b is observed. The structures of the P/C heterocycles 3a, b and 6b have been determined by NMR spectroscopy and X‐ray analysis.
Schwefel(IV)1‐Verbindungen als Liganden, 19. Kationische Ruthenium‐Sulfen‐Komplexe: Synthese und Reaktionen. Kristallstrukturanalyse von [Cp*(Me3P)2Ru(CH2SO2)]PF6
Authors: Schenk Wolfdieter A. , Urban Peter , Dombrowski Eberhard
Published: July 2007

Sulfur(IV) Compounds as Ligands, 19[1]. – Cationic Ruthenium‐Sulfene Complexes: Synthesis and Reactions. Crystal Structure Analysis of [Cp*(Me3P)2Ru(CH2SO2)]PF6

Methylene addition to coordinated sulfur dioxide yields the novel η2(C, S) sulfene complexes [Cp(dppm)Ru(CHRSO2)]PF6 (RH:3, Me: 4) and [Cp*(Me3P)2Ru(CH2SO2)]PF6 (5). An X‐ray structure determination of 5 reveals a relatively short C – S bond (167.5 pm). The sulfene complexes are powerful carbon electrophiles as shown by the rapid addition of halides, pseudohalides, amines, including „nonnucleophiles”︁ such as ethyldiisopropylamine and DBU, and phosphanes to 3. The regioselectivity of the reaction of 3 with enamines is opposite to that of free sulfene, i.e. coordination of the sulfene to ruthenium effects umpolung.
Ein L3ZnOH‐Komplex als funktionelles Modell des Enzyms Carboanhydrase
Authors: Alsfasser Ralf , Ruf Michael , Vahrenkamp Heinrich
Published: July 2007

An L3ZnOH Complex as a Functional Model of the Enzyme Carbonic Anhydrase

The tridentate ligand hydrotris(3‐tert1‐butyl‐5‐methylpyrazolyl)borate (L3) reacts with zinc perchlorate hexahydrate to form L3ZnOH (1) which is the first mononuclear neutral zinc hydroxide complex. 1 is a structural model of the enzyme carbonic anhydrase due to its tetrahedral coordination with three N‐heterocycles and one OH ion as ligands. Its functional analogy to the enzyme involves (a) reversible uptake of CO2 forming the unstable bicarbonate complex L3ZnOCOOH (4) in solution from which the dinuclear carbonate complex L3ZnOC(O)OZnL3 (3) crystallizes, (b) reaction with dialkyl pyrocarbonates forming the complexes L3ZnOC(O)OR (5) which are stable esters of the bicarbonate complex and which are easily hydrolyzed to ROH, CO2, and L3ZnOH, (c) thermal decarboxylation of the ethyl carbonate complex 5b resulting in the ethanolate complex L3ZnOEt (6) which is extremely sensitive to hydrolysis, (d) “inhibition” by small anions due to conversion of 1 into the complexes L3ZnX (7; XCl, CN, N3, OAc). The identity of the various L3Zn derivatives is established by NMR methods and structure determinations.
(E, Z)1‐Equilibria, 17 Demonstration of the Nitrogen Inversion Mechanism of Imines in a Schiff Base Model
Authors: Knorr Rudolf , Ruhdorfer Jakob , Mehlstäubl Johann , Böhrer Petra , Stephenson David S.
Published: July 2007

Experimental differentiation between pure CN double bond rotation and nitrogen inversion in N1‐arylimines is possible with a single compound (13b) under the proviso of slow rotation about the N–aryl single bond. Labelling by 1H and 13C nuclei at the diastereotopic faces of the CN moiety as well as of the N–aryl group is the clue to a successful stereodynamic analysis, as performed by variable‐temperature NMR spectroscopy of 13b, a sterically congested and chiral model compound. Interpretation of similar measurements on a second model (13d) is less straightforward. The experimental observation of time‐averaged Cs symmetry by NMR coalescences is only compatible with a mechanism of (E/Z) stereomutation either by pure inversion at sp2 nitrogen or by a contribution from CN rotation together with a synchronized (geared) controtation about the N–aryl single bond. However, the latter combination is concluded to be predominantly inversion‐like by comparisons with related imines.
A Cholestenyl‐Substituted Bis(indenyl)zirconocene‐Derived Homogeneous Ziegler Catalyst for Stereoselective Propene Polymerization
Authors: Erker Gerhard , Aulbach Michael , Wingbermühle Doris , Krüger Carl , Werner Stefan
Published: July 2007

(–)1‐5‐Cholesten‐3β1‐yl tosylate (6) undergoes SN2 substitution with indenyllithium to give (–)1‐3‐(5‐cholesten‐3α1‐yl)indene (7), which is subsequently deprotonated by methyllithium to give the cholestenyl‐substituted indenyllithium reagent 8. Its reaction with 0.5 molar equivalents of ZrCl4(THF)2 furnished the three bis[3‐(5‐cholesten‐3α1‐yl)indenyl]ZrCl2 diastereoisomers in a ratio of 9a: 9b: 9c60 : 16 : 24. The major organometallic reaction product 9a was recovered isomerically pure and used for the generation of an active homogeneous metallocene/alumoxane Ziegler‐type catalyst for stereoselective propene polymerization. The catalyst derived from the non‐bridged chirally substituted bis(indenyl)zirconocene complex 9a produces partially isotactic polypropylene almost completely by enantiomorphic site control in the temperature range from – 50 to + 15°C.
Michael‐Type Reactions between Electron‐Deficient 1,3‐Dienes and Dimethylgermylene/Water
Authors: Wienken Stefan , Neumann Wilhelm P.
Published: July 2007

A new type of reaction between dimethylgermylene (Me2Ge) (1), generated in situ from a 7‐germanobornadiene, and electron‐deficient 1,3‐dienes RR′CCH – CHCH – Z [ZC(O)Me, CO2R″ 2a – f] or cyclic dienones 8, 9 in the presence of water is described. The Michael‐type behaviour of the system Me2Ge/H2O is clearly shown by the nucleophilic addition to the unsaturated systems resulting in the formation of β1‐ and δ1‐adducts, the new allylgermanes 3a – g, 4a –c, 10a, b, 11. The cis configuration of the resulting double bond of the δ adducts 4a–c is remarkable. With open‐chain dienes cycloaddition of 1 without participation of water, yielding germacyclopentenes 5a, b or germacyclopentanes 7a, b, competes with the Michael‐type reaction. A slight variation of the substitution pattern of the dienes has a strong influence on the reaction course.
Synthese homochiraler 3‐Oxa‐2,7‐diazabicyclo[3.3.0]octane aus Aminosäuren durch intramolekulare 1,3‐dipolare Cycloaddition von Nitronen
Authors: Aurich Hans Günter , Frenzen Gerlinde , Gentes Christian
Published: July 2007

Synthesis of Homochiral 3‐Oxa‐2,7‐diazabicyclo[3.3.0]octanes from Amino Acids by Intramolecular 1,3‐Dipolar Cycloaddition of Nitrones

N1‐Allylamino alcohols 9 were prepared from amino acids by various methods. Swern oxidation of 9 afforded aldehydes 11. By reaction of 11 with N1‐alkylhydroxylamines nitrone intermediates 4 were formed which spontaneously underwent an intramolecular 1,3‐dipolar cycloaddition to yield the bicyclic compounds 6. The cycloaddition proceeds diastereoselectively furnishing homochiral compounds 6 from homochiral starting materials. The structure of 6aA was confirmed by X‐ray structural analysis.
Synthesis and Crystal Structure of the First “1,2‐Diphospha[4]radialene”
Authors: Brieden Walter , Kellersohn Thomas
Published: July 2007

1,2‐Diphosphetane 4, the first “1,2‐diphospha[4]radialene”, has been prepared in 83% yield by the reductive coupling reaction of 2,3‐bis(chloroisopropylphosphanyl)butadiene 3a with lithium in THF. The X‐ray crystal structure of 4 was determined, and it shows that 4 is a highly strained 1,2‐diphosphetane.
Beiträge zur Chemie des Bors, 216. Über die Komplexbildung von 1,3,2,4‐Diphosphadiboretanen mit Pentacarbonylchrom sowie über die Darstellung und Reaktivität von Borylidenphosphan‐Komplexen
Authors: Linti Gerald , Nöth Heinrich , Paine Robert T.
Published: July 2007

Contributions to the Chemistry of Boron, 216[1]. – On the Complex Formation of 1,3,2,4‐Diphosphadiboretanes with Pentacarbonylchromium and the Preparation and Reactivity of Borylidenephosphane Complexes

2,4‐Bis(dialkylamino)1‐1,3,2,4‐diphosphadiboretanes (R2NBP‐CMe3)2with sterically undemanding amino substituents are prepared together with the corresponding bis(phosphanyl)1‐boranes R2NB(PHCMe3)2by the reaction of R2NBCl2with Li‐P(H)CMe3. Complexes of 1,3,2,4‐diphosphadiboretanes with one or two pentacarbonylchromium fragments were obtained by the reaction of the ligands with Cr(CO)5·THF or Cr(CO)5·NMe3. If substituents are sterically demanding, cycloreversion is observed with formation of [(aminoborylidene)1‐phosphanyl‐P]pentacarbonylchromium compounds tmpBPR[Cr(CO)5] (10, 29) with an allene‐like structure. Complex29may also be prepared by HCl elimination from tmp‐B(Cl)–P(H)CMe3[Cr(CO)5] (34) with lithium diisopropylamide. This reaction can by reversed be the addition of HCl. The diphosphadiboretane11reacts with HCl, ethanol, and secondary amines with cleavage of all BP bonds. The X‐ray structures of complexes (Et2NB – PCMe3)2[Cr(CO)5]2(23) and (iPr2NB – PCEt3)2[Cr(CO)5] (25) as well as of the diphosphadi‐boretanes (Me2NB – PCMe3)2(11) and (iPr2NB – PCEt3)2(24) are presented. The intra ring angles of23remain almost unchanged upon complexation. In contrast, the B2P2ring of25is slightly folded and its noncoordinated P atom approaches a planar environment.
Metallorganische Verbindungen der Lanthanoide, 73. Synthese und Struktur neuer Monocyclooctatetraenyl‐Komplexe von Yttrium, Terbium und Lutetium
Authors: Schumann Herbert , Winterfeld Jörn , Köhn Randolf D. , Esser Lothar , Dietrich Andreas , Sun Junquan
Published: July 2007

Organometallic Compounds of the Lanthanoids, 73[1]. – Synthesis and Structure of New Monocyclooctatetraenyl Complexes of Yttrium, Terbium, and Lutetium

[(C8H8)Ln(μ1‐Cl)(THF)]2 (LnY, Lu) react with NaOR (RPh, C6H3Me2‐2,6) to give the dinuclear cyclooctatetraenyl rare earth alkoxides [(C8H8)Ln(μ1‐OR)(THF)]2 [RPh, LnY (1a), Lu (1b); RC6H3Me2‐2,6, LnY (2a), Lu (2b)]. The reactions of [(C8H8)Ln(μ1‐Cl)(THF)]2 with LiOC(tBu)3, NaOSiPh3, and NaC5H3tBu2 result in the formation of (C8H8)LnOC(tBu)3(THF) [LnY (3a), Lu (3b)], (C8H8)LnOSiPh3(THF) [LnY (4a), Lu (4b)], and (C8H8)Tb(C5H3tBu2) (5), respectively. Treatment of (C8H8)Y(C5Me5) with acetylacetone yields (C5Me5)Y(acac)2 (6). The 1H‐and 13C‐NMR and mass spectra of the new compounds as well as the X‐ray crystal structures of 1a and 5 are discussed.
The Intriguing Structural Characteristics of the Heterosiloxane Molecule Na4[Sb2O(OSiMe3)8]
Authors: Baier Michael , Bissinger Peter , Blümel Janet , Schmidbaur Hubert
Published: July 2007

Treatment of Sb(OSiMe3)3 with NaOSiMe3 in the molar ratio 1:2 in hexane at ambient temperature leads to the formation of Me3SiOSiMe3 and a crystalline complex of the formula Na4[Sb2O(OSiMe3)8] in ca. 35% yield. The composition of the product has been confirmed by elemental analysis and negative‐ion CI mass spectrometry. The single crystal X‐ray structure analysis (rhombohedral, space group R\documentclass{article}\pagestyle{empty}\begin{document}$\bar{3}$\end{document}c, Z6) resulted in a disorder model for the complex with pseudo‐cubic symmetry owing to virtually random distribution of sodium and antimony atoms over the vertices of an oxygen‐centered octahedron with the eight silyloxy groups capping the faces. Low solubility in non‐coordinating solvents prevented solution NMR studies, but solid‐state NMR investigations using cross polarization and magic‐angle spinning techniques (13C, 29Si) allowed the assignment of a point group C2v structure with the SbIII atoms in cis position relative to the oxo center of the complex.
Einkernige Nickel‐Thiolato‐Komplexe mit Nickel‐Zentren in unterschiedlichen Oxidationszuständen: Molekularer Aufbau von [Ni(SC6H4O)2]2– und [Ni(SC6H4O)2]
Authors: Köckerling Martin , Henkel Gerald
Published: July 2007

Mononuclear Nickel Thiolate Complexes Containing Nickel Sites in Different Oxidation States: Molecular Definition of [Ni(SC6H4O)2]2− and [Ni(SC6H4O)2]

Herrn Professor Dietrich Mootz zum 60. Geburtstag gewidmet.

A solution of NiCl2·6 H2O in EtOH/H2O reacts with nBu3N and o1‐mercaptophenol to form [nBu3NH]2[Ni(SC6H4O)2]·EtOH (2) containing the nickel(II) complex [Ni(SC6H4O)2]2− (1). The molecular structures of 1 and its oxidation product, [Ni(SC6H4O)2]− (3), have been determined by X‐ray diffraction. With respect to the chemical as well as electrochemical properties of the nickel sites of various hydrogenases, 3 is the first relevant model complex of coordination number four whose structural properties have been determined in different oxidation states.
Tetraindeno‐Fused Cyclooctatetraene and Oligomeric Biindenyls by Oxidative Coupling of 2,2′1‐Biindenyl
Authors: Simmross Ulrich , Müllen Klaus
Published: July 2007

Lithiated biindenyls 2 and 4, prepared by deprotonation of 2,2′1‐biindenyl (1) and 10,11‐dihydrodiindeno[1,2‐b:2′,1′‐d]thiophene (3) with n1‐butyllithium, are oxidatively coupled to give oligomeric biindenyls (17) as well as tetraindeno‐fused eight‐membered rings (16, 19, 24).
Ein neuer Weg zu isoanellierten Heteroaromaten, 1. Synthese und Reaktionen von Furofuranen, Thienofuranen, Furobenzofuranen und Benzothienofuranen
Authors: Eberbach Wolfgang , Laber Norbert , Bussenius Jörg , Fritz Hans , Rihs Grety
Published: July 2007

A Novel Route to Isoannulated Heteroaromatic Compounds, 1. – Synthesis and Reactions of Furofurans, Thienofurans, Furobenzofurans, and Benzothienofurans

A general method for the synthesis of furo‐and thienofurans 4–7 has been developed. The reaction principle is based on the thermal transformation of suitably structured epoxyhexenynes (15–19) following the general reaction sequence 1→2→3 (annulation type A). Derivatives of the so far unknown diheteropentalenes furo[3,4‐b]furan (4b, c, d, g, h), furo‐[3,4‐b]benzofuran (6b, d, e, 45) as well as benzo[4,5]thieno‐[2,3‐c]furan (7b, d) are obtained by short‐time thermolysis. Likewise two representatives of the previously reported thieno[2,3‐c]furan system are prepared (5b, c). By flash vacuum thermolysis the benzo‐annulated epoxyhexenyne 19b rearranges in poor yield to the isobenzofuran 52 (identified as dimethyl acetylenedicarboxylate adduct 47) and 2‐cyano‐α1‐naphthol (46). The structure of the furo[3,4‐b]furan 4b has been established by X‐ray structural analysis. A mechanistic explanation of the transformation of the epoxyhexenynes to diheteropentalenes is proposed. Indications for the occurrence of carbenes as product‐determining species are obtained with the phenylcyano‐substituted oxiranes 15c, h and 17e which – in additon to the furofurans 4c, h and 6e – lead to the furylindenes 31c, h/32c, h and 41, resp. The Diels‐Alder reactivity of the furo‐and thienofurans 4g, 5b, c, and 6b has been examined.
Reaktionen an Silicium‐Silicium‐Bindungen, 3. Ein neuer Weg zur Knüpfung von Si – Ge‐und Si – Sn‐Bindungen: Hexachlordisilan‐Spaltung von Organometallphosphanen und (Trichlorsilyl)phosphan‐Recycling
Authors: Martens Reiner , Mont Wolf‐Walther Du
Published: July 2007

Reactions at Silicon‐Silicon Bonds, 3[1]. – A New Path to Si – Ge and Si – Sn Bonds: Hexachlorodisilane Cleavage of Organometalphosphanes and (Trichlorosilyl)phosphane Recycling

Trimethyl(trichlorsilyl)germane and ‐stannane (4, 5) have been prepared through hexachlorodisilane cleavage by germyl‐and stannylphosphanes R2PMMe3 (1, 2, Ri1‐C3H7, t1‐C4H9; MGe, Sn). The (trichlorosilyl)phosphane byproduct R2PSiCl3 (3) may be recycled by transmetalation and methylation steps to provide starting germylphosphane (MeGeCl3, 2 MeLi) and stannylphosphane (Me3SnCl, 3 MeLi).
Beiträge zur Chemie des Bors, 217. [2 + 2]1‐Cycloadditionsreaktionen von 9‐Fluorenyliden‐(tetramethylpiperidino)boran mit Carbonyl‐und Thiocarbonyl‐Verbindungen
Authors: Channareddy Sreelatha , Glaser Bernd , Mayer Erwin P. , Nöth Heinrich , Helm Scott W.
Published: July 2007

Contributions to the Chemistry of Boron, 217[1]. – [2 + 2] Cycloaddition Reactions of 9‐Fluorenylidene(tetramethylpiperidino)borane with Carbonyl and Thiocarbonyl Compounds

Amino‐9‐fluorenylidene‐borane 1 reacts with acetone or benzophenone in a [2 + 2] cycloaddition manner to give stable 1,2‐oxaboretane derivatives 2. Aldehydes behave similarly but the oxaboretanes formed decompose readily. The esters MeCO2Et and MeCC – CO2Me as well as Cp(CO)2Fe – COCH3 also provide access to novel oxaboretane derivatives (2e, f, h). In contrast, no oxaboretane is obtained from 1 and MeC(O)NMe2 and only (tmpBO)n (n2, 3) was isolated as a decomposition product. The amides MeC(O)NHMe and MeC(O)NH2 also provide no access to cycloaddition since their NH bonds insert into the BC double bond of 1. Thioketones react with 1 to yield 1,2‐thiaboretanes 5. Tetramethyl‐cyclobutan‐1‐one‐3‐thione 8 adds 1 at its carbonyl function regiospecifically to form 9. No reaction between 1 and CO2 was observed, but COS produces an 1,2‐oxaboretane‐4‐thione 7, and CS2 in the form of [CpFe(CO)2]2CS2 the corresponding 1,2‐thiaboretane‐4‐thione 10. Analogously, the ketimine Ph2CNMe adds to 1 producing the 1,2‐azaboretidine 11. X‐ray structure determination of the 1,2‐oxaboretane 2h reveals a butterfly structure (folding anlge: 159.9°) of the four‐membered ring in contrast to the 1,2‐thiaboretane 5a whose four‐membered ring is almost planar, the folding angle being 176.9°.
Zur Kenntnis der Reaktionen von Mes2GeX2 (XF, Cl) mit [LiPH2(dme)]: Synthese von 1,1,4,4‐Tetramesityl‐2,3,5,1,4‐triphosphadigermolan
Authors: Drieß Matthias , Pritzkow Hans
Published: July 2007

Concerning the Reactions of Mes2GeX2 (XF, Cl) with [LiPH2(dme)]: Synthesis of the 1,1,4,4‐Tetramesityl‐2,3,5,1,4‐triphosphadigermolane

Mes2GeX2 (Mes2,4,6‐trimethylphenyl; XF, Cl) reacts with [LiPH2(dme)] (dmedimethoxyethane) in a 1:2 molar ratio to yield the first 2,3,5,1,4‐triphosphadigermolane derivative 3 as major product. Along 3, the monosubstituted compound Mes2Ge(PH2)Cl (4) and the 1,1,3,3‐tetramesityl‐substituted 2,4,1,3‐diphosphadigermetane (2) are formed by the reaction of Mes2GeCl2 with LiPH2 and were characterized by 31P‐NMR spectroscopy. Surprisingly, Mes2GeF2 instead of Mes2GeCl2 does not give 2. A possible mechanistic approach is presented.
Imidyl Radicals – Free‐Radical Addition of N1‐Bromoimides to Alkenes
Authors: Lüring Ulrich , Kirsch André
Published: July 2007

N1‐Bromoimides 1 add to alkenes 3 in a free‐radical chain reaction on a multigram scale with imidyl radicals 2 as chain carriers. High regioselectivities are found when the substituents at the non‐attacked sp2 carbon atom to the alkene 3 are alkoxy or sterically bulky residues. The stereochemistry of the addition is determined by the bromine transfer from the N1‐bromoimide 1 to the adduct radical 4. Formation of the trans1‐addition products 5 is favored. In competition reactions vinyl ethers react faster with the imidyl radicals 2 than alkyl‐substituted alkenes.
Sterically Hindered Free Radicals, 21. 1,2‐ and 1,4‐Additions of Diphenylmethyl Radicals to Substituted Acrylonitriles
Authors: Zarkadis Antonios K. , Neumann Wilhelm P. , Dünnebacke Dieter , Peñeñory Alicia , Stapel Ralf , Stewen Ulrich
Published: July 2007

Additions of the substituted diphenylmethyl radicals Ar11‐Ar2CR 2 (RCMe3, SiMe3, GeMe3, SnMe3, OSiMe3, CF3, CO2Me, CN) to various acrylonitriles CH2C(X)CN 3 (XSMe, SiPr, StBu, OAc, OSiMe3, OSiEt3, OMe, OEt) lead to 1,2‐5 or 1,4‐adducts 6 (ketenimines), depending mainly on the steric hindrance by the substituents R and X. Bulky substituents like tBu in 2 and tBuS in the acrylonitrile favour the formation of the extended and nearly strainless ketenimine system 6 (1,4‐adduct); smaller substituents like OSiMe3 (radical 2) and SMe, OAc, OSiMe3, OSiEt3, OMe, OEt (acrylonitrile) allow isolation of the sterically crowded 1,2‐adducts. Substituents of intermediate bulkiness like CF3 (radical 2) and SiPr (acrylonitrile) give a mixture of 1,2‐adducts (6cb, hb) and dimers 7 of the adduct radicals 4 (7cb, hb). The voluminous tBu group directly bound to the olefin (3j,k) prevents addition. The latter is generally reversible, and the various adducts 5, 6, or 7 dissociate to the adduct radicals 4 and/or fragment to the initial radicals 2 at temperatures which reflect the steric strains of the corresponding substituents R, X. The complete inertness, even toward the electron‐rich olefin 3i, of the electrophilic α1‐carbonyl‐substituted radicals 2q – s (RCHO, COMe, COPh) in the above additions is discussed. Additions of the radicals 2a – c, f, i, n, o to the conjugated olefin 3n are described and are in accordance with the conclusion that steric effects predominate in adduct formation, whereas electronic effects are of distinct but minor importance.
Synthesis of Alkyl‐Substituted Helianthrones and Mesonaphthobianthrone by Highly Regioselective Photocyclization of Bianthronylidenes
Authors: Müller Uwe , Enkelmann Volker , Adam Martin , Müllen Klaus
Published: July 2007

The synthesis of the novel alkyl‐substituted helianthrones8a, cand mesonaphthobianthrone9by photocyclization of the corresponding bianthronylidenes7a, bis described. Regioselectivity and scope of the photocyclizations of7aand7bdepend on the substitution pattern. The structures of7aand8ahave been established by X‐ray crystallography and indicate an isomerization about the central double bond of7ain the photoreaction. The structures of the protonated species of8aand9are elucidated, and their optical absorption and emission behavior is examined.
FMO Approach in [4 + 2] Cycloadditions. Kinetic Studies with 1,2‐Dimethylenecyclopentane
Authors: Sustmann Reiner , Siangouri‐Feulner Ioana
Published: July 2007

Kinetic measurements on [4 + 2] cycloadditions of 1,2‐dimethylenecyclopentane (1) as a model diene for normal Diels‐Alder reactions are described. This diene was selected in order to check whether a synperiplanar diene is a good test case for the FMO model. Using HOMO and LUMO energies from semi‐empirical quantumchemical calculations, we indeed obtained a good linear correlation between the lg k2 values and 1/(EHomo – ELUMO). The cycloadditions of E/Z isomeric dienophiles to 1 are stereospecific. These reactions are best described in terms of concerted processes.
Metallated Bicyclo[3.2.2]nona‐2,6,8‐trienes, Their Rearrangement to Barbaralanes, and a Short Synthesis of the Bicyclo[3.2.2]nona‐2,6,8‐trien‐4‐yl Anion
Authors: Blümel Janet , Köhler Frank H.
Published: July 2007

Five different anions are formed when bicyclo[3.2.2]nona‐2,6,8‐triene (1a) is deprotonated: the 6‐ and 7‐yl anions when using tBuLi/TMEDA, the 4,6‐ and 4,7‐diyl dianions when using nBuLi/tBuOK, and the 4‐yl anion (1–) after quenching the dianions with THF. Reaction of the anions with Me3SnCl gives the 6‐, 7‐, and 4‐monostannylated bicyclo[3.2.2]nona‐2,6,8‐trienes 1b, 1c, and 1d as well as the exo‐4,7‐, endo‐4,6‐, and endo‐4,7‐distannylated bicyclo[3.2.2]nona‐2,6,8‐trienes 1e, 1f, and 1g, respectively. Reaction of 1– with Me3SiCl and Me3PbCl leads to the corresponding 4‐silyl derivative 1h and its plumbyl analogue 1i. Inversely, cleavage of 1d with MeLi allows to generate 1– under particularly mild conditions. The metallation of tricyclo[3.2.2.02,4]nona‐6,8‐diene (3a), which was tested for an alternative route to 1–, gives two stannyl derivatives 3b and 3c which are substituted in the vinylic positions. – On heating 1d and 1i rearrange to yield 9‐trimethylstannylbarbaralane (2d) and its plumbyl analogue 2i quantitatively. The reactivity decreases on passing from 1i to 1d whereas 1h does not react. Mercury and zinc derivatives of 1– are so labile that only dibarbaralylmercury (2j) and ‐zinc (2k) are observed by NMR spectroscopy. The title rearrangement proceeds by a 1,5‐homodienyl metallatropic shift which involves an endo1‐type transition structure. – The new compounds 1b – i, 2d, 2i, 3b and 3c are characterized with emphasis on the NMR data including 1H, 13C, 119Sn, 207Pb signal shifts and various heteronuclear couplings.
Darstellung und Reaktionen von 1,1,2,2‐Tetraborylethan‐Derivaten
Authors: Frankhauser Pascal , Kuhlmann Frank , Krämer Albrecht , Pritzkow Hans , Siebert Walter
Published: July 2007

Synthesis and Reactions of 1,1,2,2‐Tetraborylethane Derivatives

Herrn Professor Heinrich Nöth zum 65. Geburtstag gewidmet.

Reaction of (Z)1‐1,2‐bis(dichloroboryl)ethene with B2Cl4 leads to 1,1,2,2‐tetrakis(dichloroboryl)ethane (1a) in 90% yield. Substitution of the chlorine atoms in 1a results in the formation of the iodo and amino derivatives 1b and 1c, d. Compound 1b reacts with alkynes to give the 2,2′‐linked 2,3‐dihydro‐1,3‐diborole derivatives 2b, c which are aminated to yield 2d, e. Dehalogenation of 1d leads to the organoboron C2B4 cage 3d. The heterobicyclic compound 4d with two fused phosphadiborolane rings is obtained from 1d and LiPH2. Reaction of 4d with (CO)3Fe(C8H14)2 gives the unusual diiron complex 5d. The constitutions of the new compounds are derived from spectroscopic data and are proven for 2e, 4d and 5d by X‐ray structure analyses.
Zur Komplexchemie von Cyclopentadienyl‐Liganden mit Oligoethylenglycolether‐Tentakeln
Authors: Siemeling Ulrich , Neumann Beate , Stammler Hans‐Georg
Published: July 2007

On the Complex Chemistry of Cyclopentadienyl Ligands with Oligoethylene Glycol Ether Tentacles

Herrn Professor Eckehard V. Dehmlow zum 60. Geburtstag gewidmet.

The potassium cyclopentadienides KCp′[SiMe2(OCH2CH2)m1‐OCH3]n (2) react with trimethyltin chloride to give the respective stannanes Me3SnCp′[SiMe2(OCH2CH2)mOCH3]n (3a–e). Reaction of 2a–e with iron(II) chloride affords the ferrocenes Fe{Cp′[SiMe2(OCH2CH2)mOCH3]n}2 (4a–e), which are soluble in solvents of all polarities. 4a–d were investigated with respect to their ability to act as podands for alkaline metal cations. 4c, d prove to be much better podants than 4a, b; 4a, c show a certain selectivity for K+, 4b, d show a preference for Cs+. Without rigorous exclusion of moisture, 4e yeilds the tetrasiladioxa[3](1,1‐)[3](3,3‐)ferrocenophane 5 upon prolonged standing at room temperature. The structure of 5 was determined by a single‐crystal X‐ray diffraction study. The molecule is essentially unstrained with the cyclopentadienyl rings being exactly parallel to each other; the distance between the iron atom and the ring centroid is 165 pm.
Fluktuierendes Verhalten von kationischen cis1‐Bis(ether‐phosphan)1‐palladium(II)1‐Komplexen. – 31P‐DNMR‐spektroskopische Untersuchungen, Linienformanalyse und Bestimmung der thermodynamischen Austauschparameter
Authors: Lindner Ekkehard , Dettinger Johannes , Mayer Hermann August , Kühbauch Hartwig , Fawzi Riad , Steimann Manfred
Published: July 2007

Fluxional Behavior of Cationic cis Bis(ether‐phosphane)palladium(II) Complexes. – 31P‐DNMR Spectroscopic Investigations, Line‐Shape Analysis, and Determination of Rearrangement Barriers

Herrn Professor Heinrich Nöth zum 65. Geburtstag gewidmet.

Reaction of X2Pd(P∼O)2 (XCl: 1a – g, k – n, p; XBr: 1′; XI: k″, l″, o″) with stoichiometric amounts of AgClO4 results in the formation of the monochelate complexes cis‐[ClPd(P∼O)(P∩O)][ClO4] (2a – g, k – n, p, l′, l″) (P∼O: η11‐P‐coordinated; P∩O: η21‐O,P‐chelated). In the case of compounds 1o, 1k″, and 1o″, which are provided with less basic etherphosphanes, the halide‐bridged dimers [(μ1‐X)Pd(P∼O)2]2[ClO4]2 (3o, k″, o″) are obtained. Temperature‐dependent 31P{1H}1‐NMR spectra of the fluxional complexes 2a – g, k – n, p, l′, l″ lead to δG≢ values. By using a modified version of DNMR5, computer‐generated spectra of 2a, b, f, k, l, p, l′, l″ were obtained and fitted to the experimental spectra. Graphic application of the Eyring equation to the kinetic data afforded the thermodynamic parameters δH≢, δS≢, and δG≢. The δS≢ values are in agreement with an associative exchange mechanism for 2a, b, f, l, p, l′, l″ and with a dissociative exchange mechanism for 2k, 2k and 3o crystallize in the monoclinic and triclinic space group P21/c and P&1marc; with Z4 and Z2, respectively.
OsO3F2 and OsO2F4, Preparation and Crystal Structures
Authors: Bougon Roland , Buu Ban , Seppelt Konard
Published: July 2007

The new method for preparing OsO3F2 is presented. Its crystal structure reveals a polymeric chain structure with distorted octahedral geometry for the OsO3F3 units and symmetrical, non‐linear fluorine bridges. The OsO3F3 unit has a facial geometry. This structure is not in accord with predictions on the molecular structure of OsO3F2. OsO2F4, obtained from KrF2 and OsO4, crystallizes in the space group P61 forming a sixfold helical chain arrangement of nearly octahedral OsO2F4 molecules. Oxygen or fluorine atoms are partially disordered. The cis orientation of the two oxygen atoms is established by means of NMR, vibrational spectroscopy, and X‐ray data.
Synthesis of Macrocyclic Mercury(II) Derivatives of S,S′1‐Trimethylene‐and S,S′1‐Tetramethylenebis(cis1‐stilbene‐α,β1‐dithiol) with Unusual Structures
Authors: Schrauzer Gerhard N. , Zhang Cheng , Reddy Hussain K. , Schlemper Elmer O.
Published: July 2007

The reaction of the ligand cis ‐ –SC(Ph)C(Ph)–S–[CH2]n – S – C(Ph)=C(Ph)–S– with n3 (dianion of 1) with HgCl2 in ethanol produces a yellow linearly trinuclear, μ1‐S and μ1‐Cl‐bridged complex of composition C62H52Cl2Hg3S8 (4), in which the central Hg(II) ion is in a near octahedral arrangement of four HgS and two HgCl bonds, whereas the two terminal Hg(II) ions are tetracoordinated with three HgS bonds and one HgCl bond in distorted tetrahedral arrangements. The two ligands are bidentate with respect to the terminal and central Hg(II) ions. The corresponding ligand with n4 (dianion of 2) reacts with HgCl2 to yield a yellow Hg(II) complex of composition C32H28HgS4 (5), in which the ligand is tetradentate and in the trans‐syn configuration. The Hg(II) ion in the unit cell of 5 is pentacoordinated, due to symmetric dimerization of two molecules of 2 by two weak coordinate HgS bonds of 3.442(2) Å length.
Synthesis, X‐Ray Structure and Complexation Behavior of the New Tripodal Phosphane Ligand cis, cis‐1,3,5‐Tris[(diphenylphosphanyl)methyl]1‐1,3,5‐trimethylcyclohexane (tdppmtmcy). Crystal Structure of Ir(tdppmtmcy)(CO)Cl
Authors: Mayer Hermann A. , Fawzi Riad , Steimann Manfred
Published: July 2007

The introduction of three methyl groups into the ipso positions of the cyclohexane ring in cis,cis‐1,3,5‐tris[diphenylphosphanyl)methyl]cyclohexane (tdppmcy) (1) leads to the new tripodal phosphane ligand cis,cis‐1,3,5‐tris(diphenylphosphanyl)methyl]1‐1,3,5‐trimethylcyclohexane (tdppmtmcy) (5). The dynamic behavior is studied by variable‐temperature NMR spectroscopy and compared with the structure (X‐ray analysis) in the solid state. Treatment of 5 with Ir(PPh3)2(CO)Cl gives 6 where the two PPh3 groups are replaced by two (diphenylphosphanyl)methyl groups of the ligand 5. In addition, an intramolecular CH metalation takes place resulting in the oxidative addition of a ring methylene CH bond to the metal. The X‐ray structure of 6 is determined.
Eigenschaften von Chalkogen–Chalkogen‐Bindungen, XVII. Di‐und Trisulfane mit sterisch anspruchsvollen Alkyl‐Substituenten: Das erste trans1‐Dialkyldisulfan
Authors: Ostrowski Martin , Jeske Jörg , Jones Peter G. , Mont Wolf‐Walther Du
Published: July 2007

Properties of Chalcogen–Chalcogen Bonds, XVII[1]. – Di‐and Trisulfanes with Sterically Congested Alkyl Substituents: The First trans1‐Dialkyldisulfane

Bis[tris(trimethylsilyl)methyl]trisulfane (1) is obtained from tris(trimethylsilyl)methyllithium and sulfur with subsequent oxidation by oxygen or from tris(trimethylsily)methanethiol with sulfur dichloride. The solid trisulfane contains a transoid (helical) CS–SS–C backbone without severe distortion from steric strain. Desulfuration of the byproduct bis[tris(trimethylsilyl)methyl]tetrasulfane (2) with mercury provides 1, but further desulfuration of 1 to bis[tris(trimethylsilyl)1‐methyl]disulfane (3) has not been achieved. 3 was isolated after oxidation of lithium tris(trimethylsilyl)methanethiolate with bromine. 3 contains a trans1‐CS–SC moiety with an unusually long SS bond (210–211 pm). The less crowded bis(triphenylmethyl)disulfane (4) contains a “normal” CS–SC moiety with anticlinal conformation (torsion angle – 110°).
Routes to Stannoles, Stannolenes and 1‐Stanna‐4‐bora‐2,5‐cyclohexadienes – Crystal Structure of a Triorganotin Cation Stabilized by π1‐Coordination
Authors: Wrackmeyer Bernd , Kundler Sabine , Boese Roland
Published: July 2007

Di‐1‐alkynyltin compounds (1) react with triorganoboranes R3B [2a (REt), 2b (RiPr)] to give (η21‐alkynyl)tin compounds 3 (REt) and 4 (RiPr) in which a cationic three‐coordinate tin centre is stabilized by intramolecular side‐on coordination to the CC bond of an alkynylborate fragment. An X‐ray analysis of 3e, prepared from Me2Sn(CCiPr)2 (1e) and Et3B, proves the coordination of the tin atom to the CC bond as well as a weak BC bond. An important dynamic process, i.e. exchange of the alkynyl group between boron and tin, is shown by 11B and 119Sn NMR at variable temperature. Most of the intermediates 3 react with an excess of Et3B by a second intramolecular 1,1‐ethyloboration to dialkenyltin derivatives 7 which readily rearrange to the 3‐stannolenes 8. Without an excess of Et3B, intramolecular 1,1‐vinyloboration (leading to the stannoles 5) competes with intramolecular 1,1‐ethyloboration (leading to 1‐stanna‐4‐bora‐2,5‐cyclohexadienes 9). The latter route is preferred in the case of most of the intermediates 4 (intramolecular 1,1‐isopropyloboration) and affords the six‐membered rings 10 (RiPr). 11B‐and 13C‐NMR data indicate that the heterocycles 9 (REt) adopt a flatter conformation than 10 (RiPr).
(Di‐tert1‐butylfluorsilyl)hydrazin, ein Baustein für strukturisomere N,N‐ und N,N′1‐Bis(silyl)hydrazine
Authors: Drost Christian , Klingebiel Uwe
Published: July 2007

(Di‐tert1‐butylfluorosilyl)hydrazine, a Building Block for Structure‐Isomeric N,N‐ and N,N′1‐Bis(silyl)hydrazines

Di‐tert1‐butyldifluorosilane reacts with monolithiated hydrazine to give the stable monosilylated hydrazine 1 and the six‐membered ring 2. The bis(fluorosilyl)hydrazine 3 is formed in a condensation reaction by heating 1 at 220°C. HCl elimination between 1 and chlorosilanes leads to the N,N′1‐disubstituted hydrazines 4 and 5. An N,N′1‐bis(silyl)hydrazine 6 is obtained in the reaction of lithiated 1 with difluorodiisopropylsilane while an N,N1‐bis(silyl)hydrazine 7 is formed with tert1‐butyltrifluorosilane. Structural isomerism (8–11) is observed in reactions of lithiated 1 with [(trifluorosilyl)amino]silanes.
Tri‐, Tetramethylbullvalene und Hexamethylbibullvalenyl
Authors: Rebsamen Karl , Schröder Gerhard
Published: July 2007

Tri‐, Tetramethylbullvalenes and Hexamethylbibullvalenyl

The known monomethylbullvalenes 6 and dimethylbullvalenes 7 are supplemented by tri‐8 and tetramethylbullvalenes 9 as well as the hexamethylbibullvalenyl 10. The isomer distributions of the methylbullvalenes 6–9 are determined by NMR‐spectroscopy. A vicinal arrangement of two methyl groups is not found. The 4‐, 6‐, 10‐positions are slightly preferred in respect to the 3‐, 7‐, 9‐positions. In the case of the methylbullvalenes 8 and 9 methyl groups occupy additionally the 1‐, 2‐, 8‐ but not the 5‐position. Contrary to tetrabromobullvalenes 5, isomers of 9 show no pronounced kinetic stability.
(R)1‐(+)1‐Pantolactone Acrylate as a Chiral Auxiliary in the Baylis‐Hillman Reaction
Authors: Khan Abdullah A. , Emslie Neville D. , Drewes Siegfried E. , Field John S. , Ramesar Niyum
Published: July 2007

2,6‐Dialkyl‐5‐methylene‐1,3‐dioxan‐4‐ones were prepared in good diastereomeric excess by treating pantolactone acrylate with a series of selected aldehydes in the Baylis‐Hillman reaction. With benzaldehyde and trichloroacetaldehyde, non‐cyclic products resulted. In the case of the latter aldehyde the α1‐hydroxyalkyl acrylate 5b was isolated as a single diastereomer and its absolute configuration established by X‐ray crystallography.
Stereoselective Synthesis of α,β‐trans1‐Spiro‐β1‐lactones by Diels‐Alder Cycloaddition of 1,3‐Dienes to α1‐Methylene‐β1‐lactone and Their Decarboxylation by Pyrolysis to (E)1‐Alkylidenecycloalkenes, a Convenient Olefination Method
Authors: Adam Walder , Salgado Victor Oswaldo Nava , Peters Eva‐Maria , Peters Karl , Schnering Hans Georg Von
Published: July 2007

A number of spiro‐β1‐lactones was prepared in good to excellent yields through stereoselective [4 + 2] cycloaddition of β1‐isopropyl‐α1‐methylene‐β1‐lactone (1) with acyclic, cyclic, heterocyclic and aromatic 1,3‐dienes by sealed‐tube reaction at moderate temperatures (50 – 130°C). Flash pyrolysis of the resulting spiro‐β1‐lactones 2 in the gas phase at 400°C afforded by decarboxylation exclusively the corresponding (E)1‐isopropylidenealkenes in high yields with retention of the initial geometry and without double bond isomerization. This olefination method constitutes an excellent stereoselective synthesis of (E)1‐alkylidenecycloalkenes.
1,3‐Bis(2‐thienylmethylene)1‐1H,3H1‐thieno[3,4‐c]thiophene: A Precursor for a New Low Band Gap Polymer
Authors: Hanack Michael , Schmid Ulrich , Röhrig Ursula , Toussaint Jean‐Marc , Adant Christine , Brédas Jean‐Luc
Published: July 2007

A new precursor, 1,3‐bis(2‐thienylmethylene)1‐1H,3H1‐thieno‐[3,4‐c]thiophene(9), for polyarenemethylenes (PAM), which are predicted to be low band gap polymers, is obtained by a Knoevenagel‐type condensation of 1H,3H1‐thieno[3,4‐c]thiophene 2‐oxide (7) with 2‐thiophenecarbaldehyde followed by reduction of the intermediate sulfoxide 8 with 2‐chloro‐1,3,2‐benzodioxaphosphole. Several investigations with cyclic voltammetry and UV‐Vis‐NIR spectroelectrochemistry (SEC) are carried out on 9. The experimental data are compared with the results of electronic band structure calculated on the basis of an MNDO‐optimized geometric structure by VEH pseudopotential method.
Desaminierungsreaktionen, 54. Zerfall von 1‐Cyan‐1‐propandiazonium‐Ionen
Authors: Bunse Michael , Kirmse Wolfgang
Published: July 2007

Deamination Reaction, 54[1]. – Decomposition of 1‐Cyano‐1‐propanediazonium Ions

The nitrous acid deamination of 2‐aminobutanenitrile (9) was studied with regard to product distribution and stereochemistry. The formation of 2‐(hydroxyimino)butanenitriles (21, 22; 8 – 28%) indicates the intervention of 1‐cyanopropyl radicals (24) that are captured by NO. The polar reactions lead mainly to elimination (10 – 13) and nucleophilic substitution (14 – 16), rearrangement playing a minor role. (R)‐9 was prepared from (R)1‐2‐aminobutanoic acid. The nitrous acid deamination of (R)‐9 afforded the cyanohydrin 16 with 81% net inversion. Owing to destabilization of the carbocation 26 by CN, the SN2 route of nucleophilic displacement is preferred over SN1. The influence of CN is shown to be smaller than that of CF3.
Desaminierungsreaktionen, 55. Zerfall von 2‐Cyannorbornan‐2‐diazonium‐Ionen
Authors: Kirmse Wolfgang , Minkner Dirk , Siegfried Rainer
Published: July 2007

Deamination Reactions, 55[1]. – Decomposition of 2‐Cyanonorbornane‐2‐diazonium Ions

The epimeric 2‐aminonorbornane‐2‐carbonitriles (8a and 9a) were prepared from norbornane‐2‐one (7). The nitrous acid deamination reactions of 8a and 9a afforded the nitro compounds 15c and 16c in low exo/endo ratios, presumably by way of 2‐cyano‐2‐norbornyl radicals (12). The major ionic process was found to be a Wagner‐Meerwein rearrangement, leading to 1‐cyano‐2‐norbornyl cations (10) and products 14 derived therefrom. Minor amounts (≤10%) of 2‐hydroxynorbornane‐2‐carbonitriles (15a, 16a) provide suggestive, albeit inconclusive evidence for the trapping of 2‐cyano‐2‐norbornyl cations (11). The decomposition of the endo diazonium ions 9c is also associated with norbornyl → norpinyl rearrangement, giving rise to 17 (≤9%). Stereochemical studies with optically active precursors point to intervention of the 7‐bridged norbornyl cation 13 and of the edge‐protonated cyclopropane 25. The formation of both species is clearly promoted by the cyano group.
[4 + 2]‐Cycloadditionen von Halogenthiazylen an 2‐Chlorpentafluor‐1,3‐butadien
Authors: Boese Roland , Haas Alois , Heβ Thomas
Published: July 2007

[4 + 2] Cycloadditions of Halogeno Thiazyls with 2‐Chloropentafluoro‐1,3‐butadiene

Reactions of (XSN)n (n=3, 1; X=Cl, F) with 2‐chloropentafluoro‐1,3‐butadiene provide the 1λ4,2‐thiazines 1a and 1b. Fluorination with KF converts 1a in 88% yield to 1b. CH3OH reacts with 1b to form the 1‐methoxy derivative 1c. The structure of 1c was determined by single‐crystal X‐ray diffraction analysis. With water 1a forms the 1,2‐thiazin‐3‐one 1‐oxide 2.
Benzylgalliumverbindungen. Koordination von Benzylliganden in Cs[(PhCH2)2GaF2]
Authors: Neumüller Bernhard , Gahlmann Frank
Published: July 2007

Benzylgallium Compounds. Coordination of Benzyl Ligands in Cs[(PhCH2)2GaF2]

Dissolving (PhCH2)3Ga (1) in THF yields the complex [(PhCH2)3Ga · THF] (2). Reaction of 1 with dry oxygen in toluene at –78°C leads to [(PhCH2)2GaOCH2Ph]2 (3), which is also formed from 1 and PhCH2OH. The salts K[(PhCH2)2GaF2] (5) and Cs[(PhCH2)2GaF2] (6) were obtained from (PhCH2)2GaCl (4) and KF or CsF, respectively, in acetonitrile. Crystal structures were determined for 2, 3, 6 and {[(PhCH2)2GaCl]2 · toluene} (7). Gallane 2 is a chiral monomeric complex in the solid state. The benzyl substituents create a propeller‐shaped molecule with a counterclock‐wise orientation of the ligands. 3 and 7 are crystallizing as centrosymmetrical dimers with Ga2X2 rings (X=O, Cl). 6 consists in infinite chains of {Cs[(PhCH2)2GaF2]}2 units with Cs–F contacts. In addition to the Cs–F interaction, the coordination of each Cs+ ion by two phenyl rings in a η6‐ fashion is observed.
Synthesen und Struktur von Diborylacetylenen
Authors: Schulz Hartmut , Gabbert Gernot , Pritzkow Hans , Siebert Walter
Published: July 2007

Syntheses and Structure of Diborylacetylenes

Reactions of bis(trimethylstannyl)acetylene with 2‐chloro‐1,3,2‐benzodioxaborole derivatives or 9‐chloro‐9‐borabicyclo[3.3.1]nonane lead to the corresponding diborylacetylenes 1a, b and 2. Sodium acetylide reacts with R1R2BCl to give R1R2BC1 (3a, b), which are converted to R1R2BC1R1R2 (4a, b) by lithiation and subsequent treatment with more R1R2BCl (R1=iPr2N, R2=iPr2N or tBu). X‐Ray structure analyses are performed for 1a, 4a, and 4b.