bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis and Properties of Vinylogous 6‐(Cyclopentadienyl)pentafulvenes
Authors: Eiermann Matthias , Stowasser Bernd , Hafner Klaus , Bierwirth Klaus , Frank Anette , Lerch Alexander , Reußwig Jürgen 
Published: July 2007

AbstractThe application of the principle of kinetic stabilization on vinylogous 6‐(cyclopentadienyl)pentafulvenes 1 led to the synthesis of the di‐ and tetra‐tert‐butyl derivatives 7a – e and 8a ‐ c. Their reactions with bases and acids form charged, heteroatom‐free cyanine‐type carbanionic 9a ‐ e, 10a – e and carbocationic ll a – e, 12a – c species which were characterized with NMR and UV/Vis spectroscopy. Conclusions on the ion pair structures of the alkali metal salts 9a ‐ e and 10a – c are drawn from the spectroscopic data. Additionally, in one case the behavior of the alkali metal salt 10b towards oxidants was studied by cyclic voltammetry and the structure of the corresponding hydrocarbon 8b was proved by X‐ray structural analysis.
Notizen / Notes. Probing Diazonium Ion ‐ Crown Ether Molecular Complexes bv Tandem Mass Spectrometry (FAB‐MS/MS) Acid‐Base Chemistry Within a Cluster
Authors: Laali Khosrow 
Published: July 2007

AbstractThe molecular complexes (cluster ions) formed between various aromatic diazonium ion salts ArN2⊕BF4⊖ and 18‐crown‐6 host molecules are studied by FAB mass spectrometry. The nature of the interaction is probed by MS‐MS experiments in which the ArNF (crown) 1:1 complexes are mass‐selected and subjected to collisionally activated dissociation (CAD), using helium as collision gas. The results suggest that acid‐base chemistry (proton and hydride transfer) occurs within the guest ‐host complex. Precedented mechanistic pathways for ArN2⊖ dediazoniation in the condensed phase are used as guidelines to explain these observations.
Synthesis and Reactivity of Functionalized Dimethylsilyl Complexes of the Formula (η5‐C5H5)Re(NO)(PPh3)(SiMe2X); New Base‐Stabilized Silylene Complexes, Novel Lewis Acid Adducts, and Evidence for Base‐Free Silylene Complexes
Authors: Lee Kenneth E. , Arif Atta M. , Gladysz John A. 
Published: July 2007

AbstractReactions of (η5‐C5H5)Re(NO)(PPh3)(SiMe2H) (1) and CHCl3, CBr4, and CHI3 give halosilyl complexes (η5‐C5H5)Re(NO)‐(PPh3)(SiMe2X) [X = Cl (2), Br (3), I (4); 66–84%]. Addition of Me3SiOTf to 2 gives triflate (η5‐C5H5)Re(NO)(PPh3)(SiMe2OTf) (5; 97%), which in turn reacts with (Me2N)3S⊕ [SiMe3F2]⊖ to give (η5‐C5H5)Re(NO)(PPh3)(SiMe2F) (6; 77%). Reaction of 5 and pyridine gives the base‐stabilized silylene complex [(η5‐C5H5)Re(NO)(PPh3){SiMe2(NC5H5)}]⊕ TfO⊖ (7; 84%). CH2Cl2 solutions of (η5‐C5H5)Re(NO)(PPh3)(CH3) (8) or 2 and Lewis acids are studied by IR and NMR. As assayed by IR, 8/ECl3 solutions (E = B, Al) show ReNO–ECl3 (major) and Re–ECl3 (minor) adducts. Solutions of 2/BCl3 show analogous adducts (‐78°C), and in the presence of excess BCl3 (η5‐C5H5)Re‐(NO–BCl3)(PPh3)(SiMe2Cl) (11) crystallizes. Solutions of 2/AlCl3 show uncomplexed 2 and Re–AlCl3 (major) and ReNO–AlCl3 (minor) adducts. In contrast to 2–7 and 2/BCl3, 1H‐ and 13C‐NMR spectra of 2/AlCl3 suggest an equilibrium with the base‐free silylene complex [(η5‐C5H5)Re(NO)(PPh3)‐( = SiMe2)]⊕ X⊖.
Makrocyclisch modifizierte Verbindungen vom TTF‐ und TCNQ‐Typ
Authors: Vögtle Fritz , Alfter Frank , Steckhan Eberhard , Mavili Semra , Nieger Martin 
Published: July 2007

Molecules of the TTF and TCNQ Type with Macrocyclic SkeletonsThe electron‐rich and electron‐poor macrocycles 1 – 3 have been synthesized. Their [1.1](3,3′)biphenylophane framework is formed by Kharasch reaction. Whereas in the well‐known donors and acceptors I–III the functionalities are conjugated, in their macrocyclic “analogues” 1–3 the conjugation is prevented by the meta‐connection of the phenylene rings. The redox properties —studied by cyclovoltammetry — are discussed. The X‐ray analysis of 3 shows considerable deviations from a planar structure.
(Butadien)(cyclopentadienyl)niob‐Komplexe
Authors: Herberich Gerhard E. , Englert Ulli , Linn Klaus , Roos Peter , Runsink Jan 
Published: July 2007

(Butadiene)(cyclopentadienyl)niobium ComplexesThe known bis(butadiene)(cyclopentadienyl)niobium complex (C5H4R)Nb(C4H6)2 (1, RH) exists in solution as a 1 : 1 mixture of a bis(cis‐butadiene) isomer 1a and a (cis‐butadiene)(trans‐butadiene) isomer 1b. In solution the barrier to isomerisation is 80 ± 2 kJ/mol. New derivatives 2 (RMe) and 3 (RSiMe3) of 1 are described. One of the butadiene ligands in 1 – 3 is readily substituted with CO, CNtBu, P(OMe)3, and PMe3. CpNb(PMe3)2(C4H6) (7) reacts with disubstituted acetylenes to form acetylene complexes CpNb(PMe3)(C4H6)(RCCR') (8: R, R'=Ph, 9: RMe, R'=Ph, and 10: RPh, R'=SiMe3), The structure of 9 resembles that of bent metallocene derivatives with the acetylene acting as a 2‐e ligand.
(Benzol)osmium(II)‐Komplexe mit cyclischen Oxycarben‐ und Vinylether‐Liganden
Authors: Werner Helmut , Knaup Wolfgang , Schulz Michael 
Published: July 2007

(Benzene)osmium(II) Complexes with Cyclic Oxycarbenes and Vinyl Ethers as LigandsThe compounds [C6H6Os(PR3)]2] (5, 6) react with 1‐alkynols HCCCH2CHR'OH in the presence of AgPF6 to give cyclic oxycarbene complexes (7–9) in almost quantitative yields. During the reaction vinylideneosmium intermediates are probably formed. Deprotonation of 7–9 with NaH affords the vinyl ether complexes (10 – 12). Reaction of 10 with methyl triflate (in the presence of NaH) leads to the formation of (13). The crystal and molecular structure of the oxycarbene complex 7 has been determined.
Synthese der Si‐funktionellen Acetylsilarie tBu(Me3SiCH2)[MeC(O)]SiF und tBu(Me3SiCH2)[MeC(O)]SiH sowie Synthese und Kristallstruktur des Acetylsilanols tBu(Me3SiCH2)[MeC(O)]SiOH: Substrate für mikrobielle Reduktionen
Authors: Tacke Reinhold , Hengelsberg Heidi , Klingner Etta , Henke Henning 
Published: July 2007

Synthesis of the Si‐Functional Acetylsilanes tBu(Me3SiCH2)[MeC(O)]SiF and tBu(Me3SiCH2)[MeC(O)]SiH as well as Synthesis and Crystal Structure of the Acetylsilanol tBu(Me3SiCH2)[MeC(O)]SiOH: Substrates for Microbial ReductionsThe racemic Si‐functional acetylsilanes tBu(Me3SiCH2)[MeC(O)]SiF (1) and tBu(Me3SiCH2)[MeC(O)]SiH (2) and the racemic acetylsilanol tBu(Me3SiCH2)[MeC(O)]SiOH (3) were synthesized from Si(OMe)4 (4) as substrates for microbial reductions [4 → tBuSi(OMe)3 (5) → tBu(Me3SiCH2)Si(OMe)2 (6) → tBu(Me3SiCH2)SiF2 (7) → tBu(Me3SiCH2)[CH2 = C(OMe)]SiF (8) → 1; 8 → tBu(Me3SiCH2)[CH2 = C(OMe)]SiH (9) → 2; 6 → tBu(Me3SiCH2)[CH2 = C(OMe)]SiOMe (10) → 3]. Compounds 1–3 were found to be reduced by cells of Trigonopsis variabilis (DSM 70714) [≡ SiC(O)Me → ≡ SiCH(OH)Me]. The crystal and molecular structure of 3 was studied by singlecrystal X‐ray diffraction. In the crystal, racemic 3 forms infinite chains built up by intermolecular OH…O bonds between the hydroxyl and acetyl groups of molecules of the same absolute configuration.
Synthesis and molecular structure of tin(IV) 1‐pyrrolecarbodithioates
Authors: Seth Neena , Gupta Vishnu D. , Nöth Heinrich , Thomann Martina 
Published: July 2007

AbstractThe 1‐pyrrolecarbodithioate complexes of tin, PhSnCl(S2CNC4H4)2 (1) and Sn(S2CNC4H4)4 (2) have been synthesized and characterized by IR and NMR spectra (1H, 13C and 119Sn). δ119Sn suggests hexacoordination for 1 and an even higher coordination number for 2. X‐ray structure determinations of these as well as of Me2Sn(S2CNC4H4)2 (3) have shown that 3 is one of the few known examples with a skew‐trapezoidal bipyramidal configuration. 1 attains approximately a cis‐octahedral geometry with two bidentate carbodithioate ligands with the Cl atom and the phenyl group in cis position. Complex 2 possesses two bidentate ligands while the other two are essentially anisobidentate leading to a structure between an octahedraon and a dodecahedron.
Synthesen, Strukturen und thermische Abbaureaktionen von TlI‐, PbII‐ und SeII‐Komplexen mit 2,2‐Dicyanethylen‐1,1‐diselenolat
Authors: Hummel Hans‐Ulrich , Fischer Edmund , Fischer Thomas , Gruß Ditmar , Franke Andrea , Dietzsch Wolfgang 
Published: July 2007

Preparation, Structures, and Thermal Decomposition Reactions of Complexes Consisting of TlI, PbII, and SeII and 2,2‐Dicyanoethylene‐1,1‐diselenolateThe 2,2‐dicyanoethylene‐1,1‐diselenolate‐containing compounds (AsPh4)2[Tl2(Se2C=C(CN)2)2], (AsPh4)2[Pb(Se2C=C‐(CN)2)2], and (NBu4)2[Se(Se2C=C(CN)2)2] have been prepared and characterized by single‐crystal structure analysis. The molecular structures of the complex anions 1–3 are significantly influenced by the presence of stereochemically active lone pairs. 1 is dimeric with an Se4Tl2 octahedral centre with a Tl–Tl distance of 3.547(4) Å and an average Tl–Se bond length of 3.143(4) Å. In 2 Pb constitutes the centre of a distorted pseudo‐trigonal bipyramid PbSe4E [Pb–Seave = 2.948(3) Å] with one equatorial position obviously occupied by the lonepair E. In 3 the ligands are coordinated to the central Se, which is situated in a centre of symmetry, in an undistorted way giving rise to a Ψ‐octahedral SeSe4E2 geometry [Se–Seave = 2.617(2) Å]. The compounds (AsPh4)2 · 1, (AsPh4)2 · 2 and (NBu4)2 · 3 have been decomposed thermally to yield TlSe, PbSe as well as Se. The observed contamination of TlSe and PbSe with As is avoided by using (NBu4)2 · 1 and (NBu4)2 · 2 as precursor materials.
Konkave Farbstoffe mit Azobenzol‐Einheiten als Chromophore, Photoschaltelemente und hohlraumbildende Bausteine
Authors: Bauer Martin , Vögtle Fritz 
Published: July 2007

Concave Dyes with Azobenzene Units as Chromophores, Photoswitchable and Cavity‐Forming ElementsFive monomacrocyclic (12a–e) and three types of threefold azobenzene‐bridged oligomacrocyclic compounds (15, 17, 28, 31) have been synthesized. Due to the cavity‐forming chromophores at the periphery of these molecules they represent concave dyes. The watersoluble monocycles 12b–e were photoisomerized and investigated before and after E/Z isomerization with regard to their host properties for small neutral organic guest compounds. The bicyclic azobenzene derivative 31 with triphenylethane spacers exhibits in/out isomerism. The in/out isomer 31c was separated by HPLC from 31a and b, which are in equilibrium at room temperature. The tris(2‐aminoethyl)amine‐capped Schiff bases 15 and 17 form complexes with Cu(CH3CN)4BF4.
1,2‐Dihydro‐1,3,2λ5,4λ5‐diazadiphosphet – Synthese, Struktur und Isomerisierung zum „inneren Salz”︁ von 1,3,2,4λ5‐Diazadiphosphetan‐2‐iumhydroxid*
Authors: Böske Jürgen , Niecke Edgar , Krebs Bernt , Läge Mechtild , Henkel Gerald 
Published: July 2007

1,2‐Dihydro‐1,3,2λ5,4λ5‐diazadiphosphete – Synthesis, Structure and Isomerization to the „Inner Salt”︁ of 1,3,2,4λ5‐Diazadiphosphetan‐2‐ium HydroxideThe photochemical reaction of the azidophosphane (iPr2N)2PN3 (1) with the tetraazaphospholene (3) and the bis(imino)phosphorane (Me3Si)2NP(NSiMe3)2 (6) proceeds by elimination of N2 to yield (5) and by 1,3‐silyl group shift to furnish (8) the structures of which were determined by means of NMR data and, in the case of 5, additionally by X‐ray structure analysis.
Donorsubstituierte Cyclobutenyliden–Komplexe und Cyclobutenone aus Vinyliden–Komplexen und elektronenreichen Alkinen
Authors: Fischer Helmut , Podschadly Oliver , Früh Angelika , Troll Carsten , Stumpf Rüdiger , Schlageter Andreas 
Published: July 2007

Donor–Substituted Cyclobutenylidene Complexes and Cyclobutenones from Vinylidene Complexes and Electron–Rich AlkynesPentacarbonyl(vinylidene) complexes of chromium and tungsten, (CO)5MCC(R1)R2 (1) [MW: R1R2Ph (a), R1  tBu, R2Et (b), Me (c); MCr: R1tBu, R2Me (d)] react with 1‐(diethylamino)‐1–propyne by regiospecific addition of the CC bond of the alkyne to the CαCβ bond of the vinylidene ligand to form the cyclobutenylidene complexes 2a–d. Oxidative cleavage of the cyclobutenylidene ligand from 2a–d gives the corresponding cyclobutenones. The reactions of 1b with bis(diethylamino)acetylene and of 1a with 1–ethoxy–1‐propyne afford the cyclobutenylidene complexes 3b and 4a, respectively. In contrast, 1a reacts with diorganylcyanamides, NCNR2 (RMe, Et, iPr), by ligand displacement and formation of tetraphenylbutatriene and diorganyl–cyanamide complexes. The structures of 2c and 4a were established by X–ray analyses.
Oxidation of Trimethylsilene with Molecular Oxygen — a Matrix Isolation Study
Authors: Sander Wolfram , Trommer Martin 
Published: July 2007

AbstractThe thermal oxidation of 1,1,2–trimethylsilene (1) has been investigated in O2‐doped argon matrices. The oxidation proceeds rapidly at temperatures below 40 K, and two principal oxidation products have been identified as dimethylvinylsilyl hydroperoxide (6) and dimethylvinyloxysilanol (7). The mechanism leading to these products is discussed.
Synthese und Struktur von Hexakis(trimethylsilyloxy)triarsazen
Authors: Baier Michael , Bissinger Peter , Schmidbaur Hubert 
Published: July 2007

Synthesis and Structure of Hexakis(trimethylsilyloxy)triarsazeneHexakis(trimethylsilyloxy)triarsa(V)azene [(Me3SiO)2AsN]3 (1) has been prepared from arsenic acid H3AsO4 and hexamethyldisilazane (Me3Si)2NH. According to an X‐ray crystal‐structure determination 1 features a slightly puckered six‐membered As3N3 ring. The formation of 1 proceeds with evolution of ammonia via tris(trimethylsilyl)orthoarsenate (Me3SiO)3AsO (2) as an intermediate, which could be isolated as a by‐product. The reaction of 2 with hexamethyldisilazane also gives 1 in high yields. The influence of temperature, solvent and concentration of reactants on product formation has been investigated, and side reactions are discussed.
Enantioselektive Katalyse, IX. Neue optisch reine 3,4‐Bis(phosphanyl)pyrrolidine mit Phenyl‐und Anisylgruppen sowie deren Palladium‐und Rhodiumkomplexe
Authors: Nagel Ulrich , Krink Thomas 
Published: July 2007

Enantioselective Catalysis, IX[1]. – New Optically Pure 3,4‐Bis(phosphanyl)pyrrolidines with Phenyl and Anisyl Groups Including Their Palladium and Rhodium ComplexesMethods for the synthesis of the diastereomeric mixture of the [P(R,S),3R,4R,P′(R,S)]1‐1‐(tert1‐butoxycarbonyl)1‐3,4‐bis[(2‐methoxyphenyl)phenylphosphanyl]pyrrolidines (2a, b, c) are described. For the chromatographic separation and purification of the ligand diastereomers we transformed them into the PdI21‐complexes (10a, b, c). The structure of (PR,3R,4R,P′R)1‐1‐(tert1‐butoxycarbonyl)1‐3,4‐bis[(2‐methoxyphenyl)phenylphosphanyl]pyrrolidine‐P,P′}diiodopalladium (10 b) was determined by X‐ray diffraction. Treatment of the palladium complexes with KCN yielded the pure phosphanes. The rhodium complexes (11a, 11b, 11c), which can be used as catalysts in enantioselective hydrogenations, were obtained by reaction of [Rh(COD)2]BF4 with compound 2a, 2b, or 2c.
Repetitive‐Synthesis of Bulky Dendrimers – A Reversibly Photoactive Dendrimer with Six Azobenzene Side Chains
Authors: Mekelburger Hans‐Bernhard , Vögtle Fritz , Rissanen Kari 
Published: July 2007

AbstractDendrimers with bulky repeating units containing up to 43 benzene rings (in 9) have been obtained by using a repetitive divergent synthetic strategy (three generations). The new functional dendrimer 13 containing six azobenzene units at the periphery was synthesized allowing a reversible switching of the shape and size of the molecule upon irradiation. An X‐ray structure analysis of the dendritic molecule 3a shows the inclusion of acetonitrile.
Penta‐und Hexabrombullvalene
Authors: Rebsamen Karl , Schröder Gerhard 
Published: July 2007

Penta‐and HexabromobullvalenesThe Pentabromobullvalenes 2a–d and the hexabromobullvalenes 3a/b are synthesized and the corresponding isomers are identified. 2 constitutes an equilibrium of four isomers. The isomer 2a is separated from the mixture by column chromatography. For the kinetically most stable isomer 2a the half‐life time for equilibration at 55°C amounts to ca. 30 h. Two non‐equilibrating isomers 3a and 3b are isolated, however, in the case of hexabromobullvalene 3. The bullvalene‐typical property of a fluxional structure is now practically no longer existent.
Diastereo‐ und enantioselektive Synthese 1,2‐trans‐substituierter Cycloalkancarbonsäureester und Sulfone durch Michael‐initiierte Cyclisierungen via SAMP‐/RAMP‐Hydrazone[1,2]
Authors: Enders Dieter , Scherer Hermann J. , Runsink Jan 
Published: July 2007

Diastereo‐ and Enantioselective Synthesis of 1,2‐trans‐substituted Cycloalkanecarboxylates and Sulfones by Michael‐Initiated Cyclisation via SAMP / RAMP Hydrazones[1,2]An efficient and flexible synthesis of 1,2‐trans‐substituted cycloalkanecarboxylates and sulfones of high diastereo‐ and enantiomeric purity is described. The key step of the procedure is a Michael‐initiated ring closure (MIRC) reaction employing the SAMP/RAMP hydrazone method. Depending on the chain length of the ω‐bromo(iodo)enoates 2, 3 and the type of ketone SAMP‐hydrazone 1, 3‐, 5‐, 6‐ and 7‐membered cycloalkane‐carboxylates 4–7 or cyclopentanesulfones 24 bearing two or three stereogenic centers are formed with very high asymmetric induction. In the same manner, MIRC reactions with ω‐(ethoxycarbonyl)enoate 26 give rise to 3‐substituted cyclopentanone‐2‐carboxylates 27, but with lower overall chemical yields. The relative and absolute configurations are based on X‐ray structure analyses, spectroscopic and mechanistic investigations.
Strukturen und Moleküleigenschaften sterisch überfüllter Moleküle, 36. (E)‐1,1,1,4,4,4‐Hexakis(trimethylsilyl)‐2‐buten [(H3C)3Si]3C—HCCH—C[Si(CH3)3]3 und Bis[tris(trimethylsilyl)silyl]ethin [(H3C)3Si]3Si—C≡C—Si[Si(CH3)3]3
Authors: Bock Hans , Meuret Jochen , Schödel Holger 
Published: July 2007

Structures and Molecular Properties of Sterically Overcrowded Molecules, 36[1]. — (E)‐1,1,1,4,4,4‐Hexakis(trimethylsilyl)‐2‐butene [(H3C)3Si]3C—HCCH—C[Si(CH3)3]3 and Bis[tris(trimethylsilyl)silyl]ethin [(H3C)3Si]3Si—C≡C—Si[Si(CH3)3]3The single crystal structure of an ethylene derivative, in which the two substituent half‐shells are separated by a CC spacer of about 403 pm length, shows C≡C distances of 404, 415 as well as 421 pm between non‐adjacent and of 352 pm between adjacent methyl groups, i.e. close to or within their van der Waals radii sum of 400 pm. The PE‐spectroscopically determined vertical first ionization energies of both compounds, 7.78 eV and 7.71 eV, are each the lowest ones reported so far for disubstituted ethylenes and acetylenes. Despite of irreversible cyclovoltammetric oxidation potentials, the radical cation of the six‐fold R3Si‐substituted 2‐butene can be generated by SbCl5/H2CCl2 and characterized below 230 K by its ESR spectrum.
Solvatochromism of Sterically Hindered Stilbazolium Betaines and Its Relationship to Reichardt's ET(30) Scale: The Problem of the Measurement of the Polarity vs the Acidity of Alcohols
Authors: Catalán Javier , Pérez Pilar , Elguero JosÉ , Meutermans Wim 
Published: July 2007

AbstractThe hydrogen bond acidity of twenty primary, secondary, and tertiary alkanols has been measured by the solvatochromic method by using three stilbazolium betaines: stilbazolium betaine itself (SB), o‐tert‐butyl‐substituted (TBSB), and o,o'‐di‐tert‐butyl‐substituted SB (DTBSB). The spectral differences between two of these betaines and in particular the Δ' values which correspond to SB and DTBSB, have been compared with Reichardt's ET(30) values. Excluding sterically hindered alcohols, both scales are linearly related. For normal alkanols, the Δ' values have been compared with the absorbance of the stretching of the OH band both free and associated with N,N‐dimethylacetamide (DMA). There is a linear relationship between Δ' and ln [(Av(OH)associated)/(Av(OH)free)] which proves that Δ' is a measure of the hydrogen‐bond donor (HBD) acidity of alcohols. Contrary to some expectations, the effect of alkyl substituents shows a slow attenuation with increasing number of carbon atoms in the chain.
Stereoselectivity of the Thermally Initiated Free‐Radical Chain Addition of Cyclohexane to 1‐Alkynes
Authors: Metzger JüRgen O. , Blumenstein Michael 
Published: July 2007

AbstractAlkanes can be added to alkynes in a thermally initiated free‐radical chain reaction (“ane reaction”). The addition of cyclohexane to 1‐alkynes 1a–1 yields a mixture of (Z)‐ and (E)‐2‐cyclohexyl‐1‐alkenes 3a–1. An essential step in this reaction is the addition of cyclohexyl radicals to the alkynes to give 2‐cyclohexyl‐1‐alkenyl radicals 2a–1 which abstract hydrogen from cyclohexane to yield the products 3a–1. The stereoselectivity of the addition has been measured in the temperature range of 160–260°C. It strongly depends on the substituent X of the radical center and varies over a range of almost four orders of magnitude from [(Z)‐3a]:[(E)‐3a] = 33 (X = OMe) at 160°C to [(Z)‐31]:[(E)‐31] = 0.012 (X = tBu) at 260°C. The stereoselectivity is further influenced by the temperature and in most cases by the concentration of the hydrogen donor cyclohexane. The reaction is discussed in terms of the stereoselectivity of the addition of cyclohexyl radicals to the alkyne, of the structure of the 1‐alkenyl radical (σ and π radical, respectively), the rate of inversion in the case of σ alkenyl radicals, and the relative rates of syn and anti hydrogen transfer.
Zinkkomplexe von Aminosäuren und Peptiden, 2[1]. Koordination einfacher Histidin‐Derivate an Zink
Authors: Förster Martin , Burth Rainer , Powell Anne K. , Eiche Thomas , Vahrenkamp Heinrich 
Published: July 2007

Zinc Complexes of Amino Acids and Peptides, 2[1]. – Coordination of Simple Histidine Derivatives to ZincThe bis(L‐histidine)ZnCl2 complex 1 is likely to have tetrahedral ZnN2Cl2 coordination. For the compound (L‐histidine)‐ZnCl2 · HCl (2) a structure determination has revealed a tetrahedral ZnOCl3 coordination. Of the C‐protected histidine derivatives His‐OMe and His‐NH2 and zinc salts of non‐coordinating anions the complexes (His‐OMe)2ZnX2 (3) and (His‐NH2)2Zn(ClO4)2 (4) were obtained. A structure determination of (His‐OMe)2Zn(BPh4)2 · H2O has revealed a ZnN4 coordination with chelating histidine units. Of the N‐protected histidine derivative Nα‐acetylhistidine the complexes (Ac‐His)ZnX · H2O (5, X = ClO4, BF4) have been isolated which are coordination polymers in the solid state. From pH‐dependent 13C‐NMR studies it is concluced that in solution the imidazole N and carboxyl O are coordinated to zinc in (Ac‐His)Zn and (Ac‐His)2Zn units. The doubly protected histidine derivative Bz‐His‐OMe acts as a monodentate ligand forming the tetrahedral complexes (Bz‐His‐OMe)4Zn(ClO4)2 (6) and [(Bz‐His‐OMe)2Zn(2,9‐dimethyl‐o‐phenanthroline)](ClO4)2 (7).
Kleine Ringe, 78. Tri‐tert‐butyl(trimethylsilyl)cyclobutadien und Tri‐tert‐butyl(trimethylsilyl)tetrahedran
Authors: Maier Günther , Born Dieter , Bauer Ines , Wolf Reinhard , Boese Roland , Cremer Dieter 
Published: July 2007

Small Rings, 78[1]. ‐ Tri‐tert‐butyl(trimethylsilyl)cyclobutadiene and Tri‐tert‐butyl(trimethylsilyl)tetrahedraneThe chemistry of diazo(1,2,3‐tri‐tert‐butylcyclopropenyl)(trimethylsilyl)methane (6) is unexpectedly diverse. Upon irradiation it fragments exclusively into the acetylenes 7 and 8. Flash thermolysis, on the other hand, gives — aside from the two acetylenes — tri‐tert‐butylazete (10) and trimethylsilyl cyanide (11). Upon heating 6 presumably isomerizes via betaine 17 to Dewar‐diazabenzene 13 — which is split into 10 and 11 — and diazabenzvalene 18. This reaction course is supported by the isolation of the carbonyliron complexes 15 and 16, — The CuCl‐catalyzed thermal decomposition again follows a different route. Under these conditions tri‐tert‐butyl(trimethylsilyl)cyclobutadiene (5) is formed, probably as a weak CuCl complex. Only after addition of ethylenebis(diphenylphosphane) free cyclobutadiene 5 can be isolated. Upon irradiation of 5 a quantitative isomerization to tri‐tert‐butyl(trimethylsilyl)tetrahedrane (29) occurs. This second, spectroscopically unequivocally confirmed tetrahedrane melts at 179°C. In solution the isomerization to cyclobutadiene 5 starts at about 160°C. That means, it is thermally even more stable than tetra‐tert‐butyltetrahedrane.