Spectroscopic characterization of molybdenum dinitrogen complexes containing a combination of di- and triphosphine coligands: 31P NMR analysis of five-spin systems

The three molybdenum-N2 complexes [Mo(N2)(dpepp)(depe)] (1), [Mo(N2)(dpepp)(dppe)] (2), and [Mo(N2)(dpepp)(1,2-dppp)] (3), all of which contain a combination of a bi- and a tridentate phosphine ligand, were prepared and investigated by vibrational and (31)P NMR spectroscopy. As a tridentate ligand bis(2-diphenylphosphinoethyl)phenylphosphine (dpepp) has been employed. The three different bidentate ligands are 1,2-bis(diethylphosphino)ethane (depe), 1,2-bis(diphenylphosphino)ethane (dppe), and R-(+)-1,2-bis(diphenylphosphino)propane (1,2-dppp). N-N as well as metal-N vibrations of 1-3 are identified and interpreted in terms of the geometric and electronic structures of the complexes. (31)P NMR spectra are recorded and fully analyzed. Moreover, correlation spectroscopy (COSY)-45 measurements are performed to determine the relative signs of coupling constants. Special attention is directed to a detection of different isomers and their (31)P NMR, as well as vibrational spectroscopic properties. The implications of the results for the area of synthetic nitrogen fixation with phosphine complexes are discussed.     

Pd(II) phthalocyanine-sensitized triplet-triplet annihilation from rubrene

Upconverted yellow singlet fluorescence from rubrene (5,6,11,12-tetraphenylnapthacene) was generated from selective excitation (lambdaex = 725 nm) of the red light absorbing triplet sensitizer palladium(II) octabutoxyphthalocyanine, PdPc(OBu)8, in vacuum degassed toluene solutions using a Nd:YAG/OPO laser system in concert with gated iCCD detection. The data are consistent with upconversion proceeding from triplet-triplet annihilation (TTA) of rubrene acceptor molecules. The TTA process was confirmed by the quadratic dependence of the upconverted delayed fluorescence intensity with respect to incident light, measured by integrating the corresponding kinetic traces as a function of the incident excitation power. In vacuum degassed toluene solutions, the red-to-yellow upconversion process is stable under continuous long wavelength irradiation and is readily visualized by the naked eye even at modest laser fluence (0.6 mJ/pulse). In aerated solutions, however, selective excitation of the phthalocyanine sensitizer leads to rapid decomposition of rubrene into its corresponding endoperoxide as evidenced by UV-vis (in toluene), 1H NMR (in d6-benzene), and MALDI-TOF mass spectrometry, consistent with the established reactivity of rubrene with singlet dioxygen. The upconversion process in this triplet sensitizer/acceptor-annihilator combination was preliminarily investigated in solid polymer films composed of a 50:50 mixture of an ethyleneoxide/epichlorohydrin copolymer, P(EO/EP). Films that were prepared under an argon atmosphere and maintained under this inert environment successfully achieve the anticipated quadratic incident power dependence, whereas air exposure causes the film to deviate somewhat from this dependence. To the best of our knowledge, the current study represents the first example of photon upconversion using a phthalocyanine triplet sensitizer, furthering the notion that anti-Stokes light-producing sensitized TTA appears to be a general phenomenon as long as proper energy criteria are met.     

Novel bromination reagents · hexabromocyclopentadiene: bromination of activated saturated sites

Hexabromocyclopentadiene (HBC) readily brominates α-keto and benzylic sites, apparently by bromonium ion transfer.     

Evaluation of MNDO calculated proton affinities

A large set of charged species arising mainly from protonation or deprotonation of hydrocarbons, alcohols, ethers, carboxylic acids, amines, imines, and nitriles has been studied by means of the semiempirical self-consistent-field (SCF ) molecular orbital (MO ) MNDO method. From the calculated heats of formation of such charged species and those of neutral molecules, MNDO -estimated proton affinities have been obtained and the results compared with experimental gas-phase proton affinities. If the small size anions and acetylides, for which the method predicts heats of formation too large, are ruled out, the mean absolute error in calculated proton affinities is ca. 7 kcal/mol for hydrocarbons (22 acid-base pairs) and ca. 8 kcal/mol for oxygen-containing compounds (25 acid-base pairs). For nitrogen-containing molecules it is necessary to discard, in addition, the values corresponding to the protonation of alkylamines and imines in order to achieve a reasonable mean absolute error of 7–8 kcal/mol.     

Zur Kenntnis des Faktors F430 aus methanogenen Bakterien: Struktur des proteinfreien Faktors

Factor F430 from Methanogenic Bacteria: Structure of the Protein-free Factor Factor F430, the porphinoid nickel-containing coenzyme of the methylcoenzyme-M reductase of metanogenic bacteria is shown to be the 3³,8³,12²,13³,18²-pentaacid derivative of the pentamethylester F430M, the structure of which had been determined previously (see structural formulae 1 and 2 ). The structure assignment rests on chromatographic, UV/VIS-, CD-, IR-, and ¹³C-NMR-spectroscopic as well as FAB-mass spectral comparision of F430 with F430M and the pentaacid prepared by acid-catalyzed hydrolysis of F430M. In the cells of Methanobacterium thermoautotrophicum, factor F430 is present in a ‘bound’ and also, depending on the growth conditions, in ‘free’ form, the latter being defined as the part of total F430 that can be extracted from the cells under extremely mild conditions (80% EtOH at 0–4°). From the (protein)-‘bound’ form, F430 is extracted by subsequently treating the cells at 0–4° with 80% EtOH containing (e.g.), 2m LiCi. From both sources, the extracted factor is the same pentaacid, and there is no indication for the existence of a protein-free F430 species that would contain additional (covalently bound) structural elements.     

Aporphines 24. The synthesis of N-alkylderivatives of bulbocapnine and isoeorydine

The synthesis of three new racemic aporphine alkaloids ( 1b, 1c and 2 ) is reported and these alkaloids are fully characterized. The method of synthesis involved either a Bischler-Napieralski-Psehorr sequence or a Reissert alkylation-Pschorr cyclization route. The Pschorr cyclization also gave the morphinandienones 7a and 7b , respectively.     

The Ground State Energy of a Dilute Two-Dimensional Bose Gas

The ground state energy per particle of a dilute, homogeneous, two-dimensional Bose gas, in the thermodynamic limit is shown rigorously to be E₀/N=(2²/m)|ln(a²)|^–1, to leading order, with a relative error at most O(|ln(a²)|^–1/5). Here N is the number of particles, =N/V is the particle density and a is the scattering length of the two-body potential. We assume that the two-body potential is short range and nonnegative. The amusing feature of this result is that, in contrast to the three-dimensional case, the energy, E₀ is not simply N(N–1)/2 times the energy of two particles in a large box of volume (area, really) V. It is much larger.     

Multiresolution Analysis and Radon Measures on a Locally Compact Abelian Group

A multiresolution analysis is defined in a class of locally compact abelian groups G. It is shown that the spaces of integrable functions and the complex Radon measures M(G) admit a simple characterization in terms of this multiresolution analysis.