bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mehrfachbindungen zwischen Hauptgruppenelementen und Übergangsmetallen, XCVI Niob‐ und Tantalkomplexe mit Imido‐Liganden
Authors: Herrmann Wolfgang A. , Denk Michael , Dyckhoff Florian , Behm Joachim 
Published: July 2007

Multiple Bonds Between Main‐Group Elements and Transition Metals, XCVI. – Niobium and Tantalum Complexes Having Imido LigandsThe new niobium and tantalum complexes 2b and 2c of formula M[N(SiMe3)2]2(NSiMe3)(OSiMe3) (M = Nb, b; Ta, c) are accessible by the reaction of the oxychlorides MOCl3 with the lithium amide LiN[Si(CH3)3]2 in 36 and 27% isolated yield, respectively.
Synthesis and Crystal Structure of an Arsolyl Anion and Preparation of an Arsinogallate
Authors: Sendlinger Shawn C. , Haggerty Brian S. , Rbeingold Arnold L. , Theopold Klaus H. 
Published: July 2007

AbstractThe permethylated arsolyl anion C4Me4AsLi(TMEDA) (5) has been prepared; its crystal structure (determined by X‐ray diffraction) revealed an aromatic heterocycle comparable to the homologous pyrrolyl and phospholyl anions.
Reactions of 1‐Thia‐3‐azoniabutatriene Salts with Alcohols, Carbonyl Compounds, Diazoalkanes, Nitrile Oxides, Nitrones, Enamines, and Butadienes
Authors: Lubberger Hans‐Jürgen , Müller Edgar , Hofmann Josef , Fischer Helmut , Jochims Johannes C. 
Published: July 2007

Abstract1‐Thia‐3‐azoniabutatriene salts 1 react with alcohols, carbonyl compounds, diazo alkanes, nitrile oxides, nitrones, enamines, and 1,3‐butadienes in all cases at the C=S double bond to yield new types of 2‐azoniaallene salts (3, 9a, b, 13a, b, 18, 22) and other imines (2, 20). An X‐ray diffraction analysis for 9b, the reaction product of 1b with 9‐diazofluorene, confirms the proposed constitution.
Heterocumulene, 8 C4OS (4‐Thioxo‐1,2,3‐butatrien‐1‐on), C4S2 (1,2,3‐Butatrien‐1,4‐dithion) und C3S (3‐Thioxo‐1,2‐propadienyliden) ‐ Darstellung und spektroskopische Eigenschaften
Authors: Maier Günther , Schrot Jürgen , Reisenauer Hans Peter , Janoschek Rudolf 
Published: July 2007

Heterocumulenes, 8. — C4OS (4‐Thioxo‐1,2,3‐butatrien‐1‐one), C4S2 (1,2,3‐Butatriene‐1,4‐dithione), and C3S (3‐Thioxo‐1,2‐propadienylidene) ‐ Preparation and Spectroscopic PropertiesC4OS (8) is prepared by matrix photolysis and by flash pyrolysis of the precursor molecule 4, C4S2 (12) by matrix photolysis of 10, 11, and 13. Upon irradiation both 8 and 12 are split reversibly into C3S (9) and CO or CS. The IR and UV/Vis spectra of C4OS (8), C3S (9), and C4S2 (12) are reported. Quantumchemical calculations have been performed for the structures, harmonic vibrational frequencies, singlet‐triplet gaps, and electronic transition energies of 8 and 12.
Synthesen und Strukturen von cyclischen und acyclischen Vanadium(V)‐ und Molbydän(VI)‐haltigen Verbindungen
Authors: Olms Petra , Roesky Herbert W. , Keller Klaus , Noltemeyer Mathias , Bohra Rakesh , Schmidt Hans‐Georg , Stalke Dietmar 
Published: July 2007

Syntheses and Structures of Cyclic and Acyclic Compounds Containing Vanadium(V) and Molybdenum(VI)The reaction of (C2F5)2P(Cl)NSiMe3 (2) with Cl3VNSiMe3 in CH2Cl2 yields the eight‐membered ring [(C2F5)2PN2VCl2]2 (3). (CF3)2P(Cl)NSiMe3 (1) reacts with VOCl3 to form the eight‐membered ring [(CF3)2PN]3NVCl2 (4). A six‐membered ring [Ph2PN]2NVCl2 (5) can be isolated from the reaction of Ph2P(Cl)NSiMe3 with VOCl3. 1 reacts quantitatively with MoO2Cl2 and MoOCl4 to form [MoOCl3‐O‐P(CF3)2N‐SiMe3]4 (6) and (CF3)2P(Cl)N‐MoOCl3 (7), respectively. The molecular structures of 3, 5, and 6 have been determined by X‐ray diffraction.
Komplexierung von 1,3‐Dihydro‐1, 3, 10, 10‐tetramethyl‐1, 3‐dibora‐4, 5‐benzopentafulven mit Fe(CO)3‐ und CpCo‐Fragmenten: Synthese, Kristall‐ und Elektronenstruktur von Tricarbonyl[η5‐cyclopentadienyl)cobalt] [μ,η5:η4‐(1, 3‐dihydro‐1, 3, 10, 10‐tetramethyl‐1, 3‐dibora‐4, 5‐benzopentafulven)]eisen
Authors: Nagy‐Magos Zsuzsanna , Feßenbecker Achim , Pritzkow Hans , Siebert Walter , Hyla‐Kryspin Isabella , Gleiter Rolf 
Published: July 2007

Complexation of 1, 3‐Dihydro‐1, 3, 10, 10‐tetramethyl‐1, 3‐dibora‐4, 5‐benzopentafulvene with Fe(CO)3 and CpCo Fragments: Synthesis, Crystal and Electronic Structure of Tricarbonyl[(η5‐cyclopentadienyl)cobalt][μ,η5:η4‐(1, 3‐dihydro‐1, 3, 10, 10‐tetramethyl‐1, 3‐dibora‐4, 5‐benzopentafulvene)]ironReaction of the 1, 3‐dibora‐4, 5‐benzopentafulvene 1 with the isolobal organometallic fragments Co(C5H5) and Fe(CO)3 leads to the slipped triple‐decker complex 5. It is also formed when 2 is stacked with the Co(C5H5) fragment. The X‐ray structure analysis of 5 reveals that the Co(C5H5) fragment is coordinated to the 1, 3‐diborole ring, and the Fe(CO)3 group interacts with the Y‐shaped B2CC unit. An MO calculation indicates that the formation of 5 occurs by distortion of 2 (η5‐ → η4‐bonding) and complexation of the Co(C5H5) group. 5 is 16 kcal/mol more stable than its structural isomer 6.
Synthese und Reaktionen der Stereoisomeren von Tetrabenzo‐ und Tetranaphtho[a,c,g,i]cyclododecen
Authors: Bestmann Hans Jürgen , Schaper Wolfgang , Holzmann Hans Gottfried , Zimmermann Reiner 
Published: July 2007

Synthesis and Reactions of the Stereoisomers of Tetrabenzo‐ and Tetranaphtho[a,c,g,i]cyclododeceneStarting with the bis‐mercaptane 2 and the dibromide 3 (E,E)‐ tetrabenzo[a,c,g,i]cyclododecene (1a) and the Z,Z isomer 1b are stereoselectively synthesized via the racemic (a) and the meso form (b) of the bis‐thioether 4 and the disulfone 5. Acid‐catalysed rearrangement of 1a and 1b leads to the isomeric phenanthro[9,10‐a]fluoranthene derivatives 7a and 7b. Racemate, meso form, and the optically active (‐)‐SS form of the tetranaphtho compound 18 are synthesized according to 1a and 1b from racemic or optically active starting materials 14 and 15.
Regioselektive Komplexierung von [2.2]Metacyclophanen mit Triammintricarbonylchrom
Authors: Schulz Jürgen , Vögtle Fritz 
Published: July 2007

Regioselective Complexation of [2.2]Metacyclophanes with TriamminetricarbonylchromiumThe new [2.2]phanes 12, 13, 15, and 17 have been prepared. For the preparation of the known phane 16 a new route has been developed which leads to better yields and includes an interesting reduction with Raney nickel of the naphthalene ring of 15 to a tetrahydronaphthalene ring (→17). The phanes react regioselectively with triamminetricarbonylchromium, which results exclusively in the complexation of the sterically less hindered benzene ring. The bis(tricarbonylchromium) complexes of 18 and 17 were available in good yields, when two equivalents of the precursor of the tricarbonylchromium group were used. 18a was lithiated at –78°C, and the lithiated complexes were trapped with either chlorotrimethylsilane or ethyl chloroformate to yield 4‐ and 5‐substituted products in a ratio of 4:5. Ten X‐ray structures, including those of six transition metal π complexes, which were investigated and compared under the aspect of steric interactions between the tricarbonylchromium group and the substituent at the arene ring, are discussed. Interestingly, the tricarbonylchromium group shows no noticable effect on the boat‐like deformation of the benzene ring in [2.2]metacyclophanes. A new definition of the “angles of helicity” in helical [2.2]phanes is introduced.
Synthese und Röntgenstrukturanalyse luftstabiler Bis[3‐(dimethylamino)propyl]indium‐Derivate
Authors: Schumann Herbert , Görlitz Frank H. , Seuß Thomas D. , Wassermann Wilfried 
Published: July 2007

Synthesis and X‐ray Structural Analysis of Airstable Bis[3‐(dimethylamino)propyl]indium DerivativesPentacoordinate, intramolecularly base‐stabilized organoindium compounds [Me2N(CH2)3]2InBr (1), [Me2N(CH2)3]2InO2‐CCF3 (2) and [Me2N(CH2)3]2InOC6F5 (3) as well as [Me2N‐(CH2)3]2InC2H5 (4), [Me2N(CH2)3]2In(i‐C3H7) (5), and [Me2N‐(CH2)3]2In(t‐C4H9) (6) have been prepared by the reaction of indium tribromide with 3‐(dimethylamino)propyllithium and of bis[3‐(dimethylamino)propyl]indium chloride with NaO2C‐CF3, LiOC6F5, C2H5MgBr, i‐C3H7MgBr, and t‐C4H9Li, respectively. The 1H‐, 13C‐, 19F‐NMR and mass spectra of the new compounds as well as the single‐crystal X‐ray structure analysis of 1 are described and discussed.
Metallkomplexe von Farbstoffen — Übergangsmetall‐Komplexe mit 2‐(1,3‐Dioxo‐2‐indanyliden)benzimidazolinen
Authors: Schmidt Christoph , Polborn Kurt , Beck Wolfgang 
Published: July 2007

Metal Complexes of Dyes — Transition Metal Complexes of Mono‐ and Dianions of 2‐(1,3‐Dioxo‐2‐indanylidene)‐benzimidazolines2‐(1,3‐Dioxo‐2‐indanylidene)benzimidazolines (L) (1—6) react with metal salts and chloro‐bridged complexes in the presence of NaH to give the mono and bis‐N,O‐chelate complexes (L — H+)2M (M=Cu, Pd, Ni) (7—9), (L — H+)M(PR3)Cl (M=Pd, Pt; 10—15 and (L — 2H+)[Pt(PEt3)Cl]2 (16, 17). The electronic spectra of the bis(chelate) complexes show a large bathochromic shift of the absorptions in the visible region as compared to the free ligands. The structures of (L — H+)Pd(Cl)‐(PnBu3) (10) and of (L — 2H+)[Pt(Cl)PEt3)]2 (16) have been determined by X‐ray crystallography. The two heterocyclic planes in 16 are bent along the elongated central CC bond [143.2(12)pm] which gives a hip‐roof‐like structure.
Organomolybdän‐ und Organowolfram‐Reagenzien, II. über den carbonylolefinierenden μ‐Methylenkomplex aus Mo2Cl10 und vier äquivalenten Methyllithium
Authors: Kauffmann Thomas , Fiegenbaum Petra , Papenberg Michael , Wieschollek Raphael , Sander JöRg 
Published: July 2007

Organomolybdenum and Organotungsten Reagents, II. — On the Carbonyl‐Olefinating μ‐Methylene Complex from Mo2Cl10 and Four Equivalents of MethyllithiumMo2Cl10 reacts at — 70°C with 4 equivalents of methyllithium to give a methylated thermolabile molybdenum complex. At higher temperatures it forms a thermolabile carbonyl‐olefinating reagent which according to NMR data is the μ‐CH2 complex Cl3Mo(μ‐CH2)2MoCl3 (2). Reactions of 2 with aldehydes, ketones, azomethines, and epoxides are described.
Alkylchrom‐ und Alkylmangan‐Reagenzien, IV. Über die Aldehyd‐ und cheleselektive Alkylierung organischer Carbonylverbindungen mit Monoalkylchrom(III)‐Reagenzien
Authors: Kauffmann Thomas , Beirich Christoph , Hamsen Angelika , Möller Thomas , Philipp Christian , Wingbermühle Dorothea 
Published: July 2007

Alkylchromium and Alkylmanganese Reagents, IV. — On the Aldehyde and Cheleselective Alkylation of Organic Carbonyl Compounds with Monoalkylchromium(III) ReagentsMonoalkylchromium(III) reagents, prepared in crystalline form or in solution, alkylate aldehydes but normally not ketones. Ketones with a basic group (HO, MeO, Me2N) in α‐ or β‐position are methylated by MeCrCl2(thf)3, allowing the highly selective («cheleselective») methylation of such ketones in the presence of normal ketones.
Molecular Motions in Fluctional Crystals: N‐Base Adducts of Bis(1,5‐cyclooctanediylboryl) Oxide
Authors: Yalpani Mohamed , Köster Roland , Boese Roland 
Published: July 2007

AbstractThe adducts of bis(1,5‐cyclooctanediylboryl) oxide (1) with quinuclidine (2a) and with pyridine (2b) show an unusually large premelting endothermic phase transition. 2a has been investigated by 11B‐NMR spectroscopy in the solid state and at various temperatures in its mesophase. The significant differences in the lattice packings of the molecules of the thermally stable adducts of 1 with 4‐methyl‐, 3‐bromo‐, and 4‐(dimethylamino)pyridine (2c—e; X‐ray structural analysis) from those of 2a and 2b suggests that it is the unique molecular arrangement in the respective lattices of the latter two adducts which allows a smooth transition to a two‐dimensionally ordered mesophase. This is stabilized by intermolecular fluctuation of the N‐base molecules between the boron atoms of the neighbouring molecules of 1.
Gasphasen‐Reaktionen, 85[1] Darstellung und Photoelektronen‐Spektrum von Ethyldithioxo‐λ5‐phosphoran H5C2‐P(=S)2
Authors: Bock Hans , Kremer Matthias , Solouki Bahman , Binnewies Michael 
Published: July 2007

Gas‐Phase Reactions, 85[1]. – Preparation and Photoelectron Spectrum of Ethyldithioxo‐λ5‐phosphorane H5C2‐P(=S)2The first alkyldithioxo‐λ5‐phosphorane 1a is obtained by selective monomerization of its readily accessible dimer, 2,4‐diethyl‐1,3,2λ5,4λ5‐dithiadiphosphetane‐2,4‐dithione [4 (R = C2H5)], at 970 K in the gas phase and characterized by its photoelectron spectrum, which is assigned by both Koopmans' correlation and radical‐cation state comparison with the halogen derivatives FPS2 (1b) and CIPS2 (1c).
Bis(trifluormethylchalkogenyl)ketene (CF3E)2C = C = O (E = S, Se, SO2); Synthesen und Eigenschaften
Authors: Haas Alois , Praas Hans‐Walter 
Published: July 2007

Bis(trifluoromethylchalcogenyl)ketenes (CF3E)2C = C = O (E = S, Se, SO2); Synthesis and PropertiesBis(trifluoromethylchalkogenyl)ketenes (1) are synthesized either by dehydrohalogenation of the corresponding acetyl chlorides or dehydratization of the corresponding acetic acids. In addition, treatment of trifluoromethylchalkogenyl chlorides with Ag2C = C = O provides 1 a in low but 1 b in good yields. Oxidation of bis(trifluoromethylsulfanyl)acetic acid with CrO3/H2SO4 gives some bis(trifluoromethylsulfonyl)ketene 1 c. Starting materials for the preparation of the ketenes are mono‐ and bis(trifluoromethylchalkogenyl)‐substituted orthoesters which are prepared from CH3C(OC2H5)3 and CF3ECl (E = S, Se). They are hydrolyzed to CH3‐n(ECF3)nC(O)OH (4). For E = Se the acids 4b,d are converted by SOCl2 into CH3‐n(SeCF3)nC(O)Cl (7a,b). Mono‐ and disubstituted malonic esters 5, 6 are formed by treating diethyl malonate with sodium and then CF3ECl. Acidic hydrolysis with 62% HBr converts 5 and 6 into the corresponding acetic acid derivatives 4. From CH3‐n(SCF3)nC(O)Cl and (CH3)3SiN3 isocyanate CH3‐n(SCF3)nNCO (n = 1, 2) are obtained in good yields. Hydrolysis of (CF3S)2C = C = O (1a) either in acidic or basic solution gives (CF3S)2CHC(O)OH (4c). Some chemical reactions of 1 a are described.
Ester von (Hydroxymethyl)diorganylsilanen: Synthese und thermisch induzierte Umlagerung
Authors: Tacke Reinhold , Wiesenberger Frank , Becker Beate , Rohr‐Aehle Regine , Schneider Petra B. , Ulbrich Uwe , Sarge Stefan M. , Cammenga Heiko K. , Koslowski Thorsten , Niessen Wolfgang Von 
Published: July 2007

Esters of (Hydroxymethyl)diorganylsilanes: Synthesis and Thermally Induced RearrangementTwenty silanes of the type R1R2Si(H)CH2OR3 (A) were synthesized [R1, R2 = Me, Ph, 1‐naphthyl, PhCH2,Me3SiCH2; OR3 = OC(O)Me, OC(O)Ph, OC(O)CF3, OS(O)2CF3, OP(O)Ph2, OC(O)Cl] and studied for their thermal behaviour. The silanes A undergo a thermally induced rearrangement to give the corresponding silanes R1R2Si(OR3)Me (B). For compounds with OR3 = OC(O)Cl, an additional decarboxylation takes place to yield the chlorosilanes R1R2Si(Cl)Me. Except for the derivatives with OR3 = OC(O)Cl, the energetic (reaction enthalpy) and kinetic data (reaction order, frequency factor, enthalpy and entropy of activation) of these reactions were studied by means of differential scanning calorimetry (DSC). In addition, the kinetics of all reactions were investigated by 1H‐NMR spectroscopy. The transition state of the rearrangement was investigated by an ab initio study based on the model compound H3SiCH2OC(O)H [→ MeH2SiOC(O)H]. The theoretical data and the experimentally obtained energetic and kinetic data are discussed in terms of mechanistic aspects of the rearrangement reaction A → B.
Alkalimetall‐trialkylhydroxyborate und (Alkalimetalloxy)dialkylborane[1]
Authors: Köster Roland , Seidel Günter , Wrackmeyer Bernd 
Published: July 2007

Alkalimetal Trialkylhydroxyborates and (Alkalimetaloxy)dialkylboranes[1]Et3B (1) and 9‐Et‐9‐BBN (2) react with alkalimetal hydroxides (LiOH, NaOH, KOH) to yield the alkalimetal hydroxytriorganoborates M‐3 and M‐4, resp. Heating (about 100°C) of the borates, catalyzed by NaHBEt3, leads to elimination of ethane with formation of the boranes MOBEt2 (M‐5, M = Na, K) or MOBC8H14 (M‐7, M = Li, Na, K), which associate to compounds with BOB, BOM, or MOM bridge bonds. At temperatures higher than 160°C (without catalyst), M‐3 (M = Li, Na) and Li‐4 dissociate. Na‐4 is dehydroborated with formation of H2 and NaOB(Et)C8H13 (Na‐9). From K‐7 and ClSiMe3 9‐Me3SiO‐9‐BBN (10) is obtained. Na‐9 reacts with ClSiMe3 to give a mixture of the unsaturated mixed borane 11 and the mixed diboroxane 12. The degree of the association of the alkalimetal compounds were determined by the specific electric conductivity measurements (K) and by 17O‐NMR spectroscopy.
Asymmetrische Katalysen, 77[1] Neue optisch aktive Pyrazolderivate für die enantioselektive Katalyse
Authors: Brunner Henri , Scheck Thomas 
Published: July 2007

Asymmetric Catalysis, 77[1]. – New Optically Active Pyrazole Derivatives for Enantioselective CatalysisStarting from the amines 3–6 and the dipyrazolopyrazinedione 2, the optically active (pyrazolylmethyl)amines 11–14 have been synthesized. Furthermore, the preparation of the (+)‐camphor‐derived optically active pyrazole 17 is described. Pyrazoles 11–13 and 17 are introduced as chiral building blocks into the 2‐(1‐pyrazolyl)pyridines 30–33. The optically active compounds 23–25 are formed from 2‐[3(5)‐pyrazolyl]pyridine and 2,6‐bis[3(5‐)pyrazolyl]pyridine, respectively, and (+)‐3‐(bromomethyl)pinane. The pyrazole derivatives 27–29 contain (+)‐(1‐phenylethyl)hydrazine as the optically active component.
Synthese und Struktur von SeSb2Cl2(NCMe3)4 — eines nur von Stickstoffatomen umgebenen Selenimids[1]
Authors: Björgvinsson MÁR , Roesky Herbert W. , Pauer Frank , Sheldrick George M. 
Published: July 2007

Synthesis and Structure of SeSb2Cl2(NCMe3)4 – a Compound with a Selenium Atom Coordinated by three Nitrogen Atoms[1]Reaction of Se[NCMe3(SiMe3)]2 (2) with SbCl3 leads to the novel tricyclic compound SeSb2Cl2(NCMe3)4 (3). According to an X‐ray structure analysis the six‐membered SeSb2Cl2(NCMe3)3 ring in 3 is bound to the NCMe3 moiety.
Bis(methylen)phosphorane — Synthese, spektroskopische Untersuchungen und thermische Isomerisierungen zu λ3‐Phosphiranen
Authors: Becker Petra , Brombach Heike , David Gabriele , Leuer Martina , Metternich Hans‐Jürgen , Niecke Edgar 
Published: July 2007

Bis(methylene)phosphoranes – Synthesis, Spectroscopic Investigations and Thermal Isomerizations to λ3‐PhosphiranesA great number of differently substituted bis(methylene)phosphoranes 10 [R – P{ = C(SiMe3)2}2] are obtained by nucleophilic substitution from bis[bis(trimethylsilyl)methylene]‐chlorophosphorane (8). The reactions of dichlorophosphanes 1 and methylenephosphanes 3 with lithium carbenoides 2 furnish the mixed derivatives 6 [R—P( = CR1R2)( = CR3R4)] and 7 [R—P( = C(SiMe3)2( = CR3R4)]. Among these the reaction of the sterically less hindered methylenephosphanes 3c, d [R2N—P = C(H)SiMe3, R = Et, iPr] with an excess of the lithium carbenoide 2b results in the formation of the σ4λ5‐phosphiranes 11a, b {R2N – P[ = C(H)SiMe3]2}. The sterically highly demanding substituents in 10a – o render great thermal stability, while the mixed bis(methylene)phosphoranes 6, 7 rearrange to the corresponding σ4λ5‐phosphiranes 15a–o. Investigations performed between 30 and 180°C reveal that all bis(methylene)phosphoranes, with the exception of 6c, k – m and 7e, can be isomerized. – The phosphino‐substituted bis(methylene)phosphoranes 10k, 1 show different reactivity. Light‐and thermally induced cleavage of the P – P bond, and dimerization of the corresponding fragments result in the formation of 14 and the diphosphanes 13a, b. The bis(methylene)phosphoranes 10a–o are investigated by UV and NMR spectroscopy.
Synthese und Strukturen von (Monoorganyl)amiden und ‐imiden des Zirkoniums und Hafniums
Authors: Bai Yüniu , Roesky Herbert W. , Noltemeyer Mathias , Witt Michael 
Published: July 2007

Synthesis and Structures of (Monoorganyl)amides and ‐imides of Zirconium and HafniumThe tetrahalides MCl4 (M = Zr 1 a, Hf 1 b) react with LiNHtBu with elimination of LiCl to yield [(tBuNH)2MNtBu]2 (3) (M = Zr 3a, Hf 3b). Compounds 3 are thermally instable and oli‐gomerise above 100 °C with elimination of H2NtBu. The reactions of (η5‐C5Me5)MCl3 (M = Zr 1 c, Hf 1 d) with LiNHR (R = tBu 2 a,2,4,6‐Me3C6H2 2 b, 2, 6‐iPr2C6H3 2 c) lead to (η5‐C5Me5)M(NHR)3 (4) (R = tBu, M = Zr 4 a, Hf 4 b; R = 2, 4,6‐Me3C6H2, M = Zr 4 c, Hf 4 d; R = 2,6‐iPr2C6H3, M = Zr 4 e, Hf 4 f). Compounds 4 are thermally very stable and melt without decomposition. When 1 c and 1 d react with LiNHPh (2 d), dimers of composition [(η5‐C5Me5)M(NHPh)NPh]2 (M = Zr 5 a, Hf 5 b) are obtained. The complexes (η5‐C5Me5)2MCl2 (M = Zr 1 e, Hf 1 f) react with 2 b to form (η5‐C5Me5)2M(NHR)2 (6) (M = Zr 6 a, Hf 6 b). Pyridine reacts with 4 e at 85 °C and replaces one molecule of 2,6‐iPr2C6H3NH2 to give (η5‐C5Me5)Zr‐(NHR)NR · Py (7). The single crystal X‐ray structures of 4 a, 4 f, 5 b and 7 are described.
4,4′‐Distyrylazobenzol als Chromophor
Authors: Meier Herbert , Kosteyn Frank , Hanold Norbert , Rau Hermann , Gauglitz Günter 
Published: July 2007

4,4′‐Distyrylazobenzene as Chromophore4,4′‐Distyrylazobenzenes are prepared from 4,4′‐dimethylazobenzene. Whereas the Siegrist method furnishes stereoselectively the (E,E,E) configuration, a Wittig olefination leads to a mixture of (Z,E,Z), (Z,E,E) and (E,E,E) isomers which can be easily separated. Irradiation of the intense absorption at λ ≈ 400 nm causes a selective (E) → (Z) isomerization of the N = N bond of all three isomers. The reverse reaction takes part in the photochemical equilibration, moreover, it is a thermal process with a relatively low activation barrier.
Stereoselektivität von Photocycloadditionen, 5[1] Photoreaktionen zwischen 2‐Cyclopenten‐1‐on und Enolethern
Authors: Griesbeck Axel G. , Stadtmüller Stefan , Busse Holger , Bringmann Gerhard , Buddrus Joachim 
Published: July 2007

Stereoselectivity in Photocycloaddition Reactions, 5[1]. – Photoreaction of 2‐Cyclopenten‐1‐one with Enol EthersThe regio‐ and stereoselectivity of [2 + 2] photocycloaddition reactions between 2‐cyclopenten‐1‐one (1) and the electron‐rich alkenes: ethyl, isopropyl, and phenyl vinyl ether (2–4) as well as 2,3‐dihydrofuran (10) were examined. In all cases the annulated cyclobutene derivatives 5–7 and 11 were isolated in yields between 70 and 99%. The regioisomeric HT/HH products were formed in a ratio of 3:1 to 4:1. For the determination of the product stereochemistry, INADEQUATE and 1H,1‐decoupling experiments were performed. Computer‐assisted investigations on the molecular geometry and 1H,1H‐coupling constants were performed by using semiempirical methods (AM1, FINITE). The HT regioisomers were formed with moderate endo diastereoselectivity, whereas in the case of the HH regioisomers both diastereomers (exo/endo) were formed in equal amounts. Photoreaction with 2,3‐dihydrofuran (10) led to almost exclusive formation of exo‐diastereomeric HH and HT regioisomers 11. The observed stereoselectivity is rationalized by the optimal geometry of the intermediate triplet 1,4‐biradicals during intersystem crossing.
2,6‐Dicyansemibullvalen
Authors: Quast Helmut , Janiak Rolf , Peters Eva‐Maria , Peters Karl , Schnering Hans Georg Von 
Published: July 2007

2,6‐Dicyanosemibullvalene[1]Bicyclo[3.3.0]octane‐2,6‐dione (2) adds trimethylsilyl cyanide under catalysis by zinc iodide to afford a mixture of the diastereomeric O‐trimethylsilyl cyanohydrins exo,endo‐ and exo,exo‐3 (3:7). Treatment of this mixture with the hydrogen fluoride‐pyridine complex in phosphorus oxychloride as solvent and subsequent heating with an excess of pyridine yield 70% of a 1:1 mixture of the unsaturated dinitriles 4 and 5, which is separated by medium‐pressure liquid chromatography. Allylic bromination of 4 by N‐bromosuccinimide results in the formation of the Y,Y'‐dibromodinitrile 6, the configuration of which is elucidated by means of an X‐ray diffraction analysis. Reduction of 6 with the zinc‐copper couple in tetrahydrofuran under ultrasonic irradiation leads to dilute solutions of the title compound 1 a. Attempts at the isolation of 1 a were frustrated by its tendency to polymerize. The structure of 1 a is based on IR, UV, 1H‐ and 13C‐NMR spectra and a comparison with the known 1,5‐dimethylsemibullvalenedicarbonitrile (1 b).