Darstellung,Eigenschaften und Molekülstruktur eines Titan-tris(diazadien)-Komplexes

Preparation, Properties, and Molecular Structure of a Titanium-tris(diazadiene) Complex (R = i-C₃H₇) 1 was obtained by reaction of TiCl₄ · 2 THF with Li₂(NR? CH = CH? NR) in the presence of the ligand molecules. The compound was characterized by ¹H-, ¹³C-n.m.r., and mass spectroscopy. The molecular structure was determined by X-ray diffraction. The bonding distances in the identically coordinated diazadiene ligands are similar to those of radical.     

Total synthesis of verticillene,the putative biogenetic precursor of the taxane alkaloids

Intramolecular reductive coupling of the bis-aldehyde(14) in the presence of Ti(0), followed by 1,4-reduction of the resulting tetraene(16) using sodium in ammonia, provides a facile synthesis of $\text{E}$,$\text{E}$-verticillene(2), the putative biogenetic precursor of the taxane family of alkaloids e.g. (3).     

Rhodium-carbonyl complexes with a quinolyl functionalized Cp-ligand: synthesis and photochemical activation

Dicarbonyl[η⁵-2,3,4,5-tetramethyl-1-(8-quinolyl)cyclopentadienyl]rhodium(I) (1) was prepared by the reaction of [Rh(CO)₂Cl]₂ with 2,3,4,5-tetramethyl-1-(8-quinolyl)cyclopentadienyl-potassium. Irradiation of 1 in chloroform or dichloromethane as solvent leads to the formation of dichloro[η⁵-2,3,4,5-tetramethyl-1-(8-quinolyl)cyclopentadienyl]rhodium(III) (2). When Rh₆(CO)₁₆ is present, the cluster adds to the 8-quinolyl-cp-rhodium fragment and the compound [η⁵-2,3,4,5-tetramethyl-1-(8-quinolyl)cyclopentadienyl]rhodium-di-μ-carbonyl-hexarhodiumtetradecacarbonyl (3) is formed in 65% yield. The coordination sphere of the rhodium(III) atom in compound 2 and of the rhodium(I) atom in 3 is completed by a coordination of the quinolyl moiety. This was revealed by NMR spectroscopy as well as by X-ray analyses.     

Particle spin from representations of the diffeomorphism group

The semidirect productI∧K of Schwartz' spaceI of functions on ?³ with the groupK of diffeomorphisms of ?³ provides a model for quantum theory based on local currents. Certain unitary representations of ?^K are induced by representations of \(\overline {{\text{SL(3, }}\mathbb{R}{\text{)}}}\) . From the local currents in these representations, we construct the generators of local rigid rotations, with respect to which the Hilbert space decomposes into invariant subspaces of fixed spin carrying representations of local SU(2). The physical interpretation of this procedure is discussed.     

Polarizable biphenyl polysiloxane stationary phase for capillary column gas chromatography

A crosslinkable biphenylmethylpolysiloxane stationary phase was synthesized for capillary column gas chromatography and compared with methyl, phenyl, and cyanopropyl polysiloxane stationary phases for the separation of isomeric polycyclic aromatic compounds. While the new phase gave similar separations of nonpolar isomers when compared to the nonpolar phases, separations of polar isomers were greatly improved because of the induced polarity of the biphenyl group of the stationary phase by the solute molecules. This polarizable stationary phase offers a unique selectivity which is not available in other stationary phases.     

Diphosphan-tetraphenylnickelacyclopentadien

Reaction of 1,2-bis(diorganophosphino)ethanenickel dibromide (I) with 1,2,3,4-tetraphenyl-1,4-dilithiumbutadiene (II) at ?30°C yields diphosphannickelacyclopentadiene (III) which at elevated temperatures isomerizes to diphosphanecyclobutadienenickel(0) (IV). The thermodynamic and kinetic parameters of the rearrangement were determined. The structural and conformational analyses of III were carried out by means of ¹³C NMR, ³¹P NMR and Raman spectroscopy. The reactions of III and IV with CH₃COOH, CO, RCCR and RNCNR have been axamined and the observed reactivities III ? IV are discussed.     

Photoinduced carbon monoxide migration in a synthetic heme-copper complex

Time-resolved infrared (TRIR) flash photolytic techniques have been employed to initiate and observe the efficient dissociation of CO from a synthetic heme-CO/copper complex, [((6)L)Fe(II)(CO)..Cu(I)](+) (2), in CH(3)CN and acetone at room temperature. In CH(3)CN, a significant fraction of the photodissociated CO molecules transiently bind to copper (nu(CO)(Cu) = 2091 cm(-)(1)) giving [((6)L)Fe(II)..Cu(I)(CO)](+) (4), with an observed rate constant, k(1) = 1.5 x 10(5) s(-)(1). That is followed by a slower direct transfer of CO from the copper moiety back to the heme (nu(CO)(Fe) = 1975 cm(-)(1)) with k(2) = 1600 s(-)(1). Additional transient absorption (TA) UV-vis spectroscopic experiments have been performed monitoring the CO-transfer reaction by following the Soret band. Eyring analysis of the temperature-dependent data yields DeltaH(double dagger) = 43.9 kJ mol(-)(1) for the 4-to-2 transformation, similar to that for CO dissociation from [Cu(I)(tmpa)(CO)](+) in CH(3)CN (DeltaH(double dagger) = 43.6 kJ mol(-)(1)), suggesting CO dissociation from copper regulates the binding of small molecules to the heme within [((6)L)Fe(II)..Cu(I)](+)(3). Our observations are analagous to those observed for the heme(a3)/Cu(B) active site of cytochrome c oxidase, where photodissociated CO from the heme(a3) site immediately (ps) transfers to Cu(B) followed by millisecond transfer back to the heme.     

Addition compounds of nucleophiles and 3-ethylthio-6-oxo-6H-1,2-dithiolo[4,3-c]1,2-dithiolium tetrafluoroborate. Synthesis of 3H,6H-1,2-dithiolo[4,3-c]1,2-dithiole-3-one-6-thione

Summary A smooth method of synthesizing 3H, 6H-1,2-dithiolo[4,3-c]1,2-dithiole-3,6-dithione (3), and also its partial desulfuration to yield 3H, 6H-1,2-dithiolo[4,3-c]1,2-dithiole-3-one-6-thione (4) is presented. The ethylation product5 of the monothione4 reacts with various nucleophilic reagents to form remarkably stable adducts. The adducts of5 with methanol,tert-butyl mercaptan, and with aniline could be isolated and characterized by their¹H-NMR spectra.

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Anlagerungsverbindungen von Nukleophilen an 3-Ethylthio-6-oxo-6H-1,2-dithiolo[4,3-c]1,2-dithioliumtetrafluoroborat. Synthese von 3H,6H-1,2-Dithiolo[4,3-c]1,2-dithiol-3-on-6-thion

Zusammenfassung Eine glatte Synthese für 3H,6H-1,2-Dithiolo[4,3-c]1,2-dithiol-3,6-dithion (3) und für dessen partielle Entschwefelung zu 3H,6H-1,2-Dithiolo[4,3-c]1,2-dithiol-3-on-6-thion (4) wird angegeben. Das Ethylierungsprodukt5 des Monothions4 reagiert mit unterschiedlichen Nukleophilen zu bemerkenswert stabilen Addukten. Die Addukte mit Methanol,tert.-Butylmercaptan und mit Anilin wurden isoliert und durch ihr¹H-NMR-Spektrum charakterisiert.

     

Threshold-photoelectron-spectroscopy-coincidence study of the double photoionization of HBr

A threshold-photoelectron-coincidence spectrum of HBr has been recorded in the 32.2-35.8 eV photon energy range, with a resolution of approximately 0.01 eV, using a synchrotron radiation source. The X (3)Sigma(-) and a (1)Delta(2) states of the HBr(2+) dication are clearly observed in the spectrum, while there is no clear evidence for the formation of the b (1)Sigma(+) electronic state. For the first two states, the vibrational states v=0-3 have been resolved, while for the ground X (3)Sigma(-) state also spin-orbit splitting has been detected. The results appear in good agreement with previous experimental observations. A comparison with theoretical predictions indicates the role of "noncovalent" contributions to the interaction between the two atomic partners for the formation of metastable states.     

Efficient photodissociation of O2 from synthetic heme and heme/M (M = Fe, Cu) complexes

Single wavelength excitation (lambdaex = 355 or 532 nm) of low-temperature stabilized (198 K) synthetic heme-dioxygen and heme-dioxygen/M complexes, where M = copper or iron in a non-heme environment, results in the dissociation of dioxygen as indicated by the generation of the ferrous heme (Soret band, 427 nm) and the bleaching of the ferric-superoxide (FeIII(O2-)) 410-nm Soret band in the transient absorption difference spectrum. Dioxygen rebinds to the four heme complexes studied with comparable rate constants ( approximately 6-9 x 105 M-1 s-1). However, the quantum yield for complete dissociation of O2 from our simplest heme-O2 complex (F8)FeIII(O2-) (phi = 0.60) is higher than the other complexes measured (phi = approximately 0.2-0.3) as well as that for oxy-myoglobin (phi = 0.3).