The mechanism of photoinsertion of haloalkenes into Fe---C bonds of dieneiron tricarbonyls

1,1-Dichloro-2,2-difluoroethylene (like other fluoroalkenes) and dieneiron tricarbonyls react photochemically to give products in which the haloalkene has inserted into the Fe---C(1) bond of the diene complex. The reaction is regiospecific with respect to both diene and haloalkene. The reaction is shown to occur by (a) photodissociation of a CO ligand from iron; (b) π-complexation of haloalkene; (c) π → σ ligand rearrangements accompanied by CO reattachment. The adducts undergo hydrolysis on silica gel chromatography, to give substituted 2-chlorocyclohexadienoneiron tricarbonyls.     

Gehinderte ligandenbewegungen in übergangsmetallkomplexen : V. 1H-NMR-untersuchung der bewegungen des olefinliganden in cyclopentadienyl-mangan-dicarbonyl-tetramethoxyäthylen

The methoxy signals in the ¹H NMR spectrum of cyclopentadienylmanganese dicarbonyl tetramethoxyethylene, C₅H₅Mn(CO)₂[C₂(OCH₃)₄], show a definite temperature-dependence. In CS₂ solution the variations of the signals are observed within a single temperature range, while in toluene-d₈ two regions of change are found to exist. These data are explained on the basis of two mutually independent ligand movements: a hindered rotation of the olefin ligand around the metalligand bond (ΔG³₁₉₄ = 9.8 ± 0.6 kcal/mol), and a hindered movement of the four methoxy groups (ΔG³₂₆₃ = 13.8 ± 0.3 kcal/mol, both in toluene-d₈. Chiral conformations of the ligand are assumed to be formed when the movement of the methoxy substituents ceases.     

Mechanistic and synthetic aspects of the reaction of alkyl esters of phosphorus with trimethylstannyl halides

The reaction of trimethylstannyl halides with trialkyl phosphates has been studied. The results are interpreted in terms of a mechanism involving a trimethylstannyloxyphosphonium salt intermediate. The much lower reactivity of the stannyl halides compared with their silicon analogs is explained by the lower ionization of the stannyl halide phosphate complexes and the unfavourable direction of the decomposition of the phosphonium salt intermediate. The reaction may be useful in synthesis of phosphates containing only one O-stannyl group, which can be used in generation of the acid function or replaced in reactions with compounds containing active halogen.     

σ,π-acetylido complexes via P---C bond cleavage of phosphinoacetylenes: X-ray structure of Fe2(CO)6(CCPh)(PPh2)

Solutions of Co^II salts of organic acids in primary amines absorb molecular oxygen rapidly and irreversibly forming μ-dioxygen—cobalt complexes. Thermolysis leads to a homopolar cleavage of the OO bond with subsequent radical reactions involving ligand amine. After thermolysis the capacity of oxygen uptake is reestablished (catalysis).     

The structure of the proton skeleton in 1,3-butadieneiron Tricarbonyl as determined from the NMR spectra of oriented molecules

¹H NMR spectra of 1,3-butadieneiron tricarbonyl oriented in a nematic liquid crystal solvent have been analysed and used to derive the structure of the proton skeleton, which is found to be non-planar. The distance of the anti protons from the plane defined by the remaining four protons is 0.77 ± 0.06 ±.     

Resonance enhanced laser ionisation mass spectrometry of four aromatic molecules

Multiphoton ionisation and fragmentation of aniline, benzene, N,N-dimethyl and 2,4-dimethyl aniline has been studied by laser ionisation mass spectrometry under collision free conditions. All four molecules undergo efficient resonance-enhanced two-photon ionisation (R2PI) with relatively low laser intensities at λ = 266 nm producing the parent ion almost exclusively. At higher intensities, high order processes compete producing extensive fragmentation. At 266 nm, all the major fragment ions are produced by R3PI. For aniline excited at 294 nm, energetic considerations suggest R4P1 formation of fragments with differences in fragmentation between 266 and 294 nm reflecting the differing orders and energies above threshold of the competing processes. Comparison of R2P1 efficiencies in aniline and benzene shows that the cross sections for ionisation of the resonant intermediate ₁B² excited state in both molecules are approximately equal and independent of wavelength in the range 250–300 nm.     

Control of release kinetics of macromolecules from polymers

Internal and external means for controlling the release rates of large molecules, such as proteins, from ethylene—vinyl acetate copolymer matrices are presented. Internal approaches include alteration of the polymer—drug design, such as changing drug loading and particle size, coating the matrix, or altering matrix geometry. Kinetic and microstructural analyses are discussed. Applications of these polymeric systems, for instance, in delivery of insulin for diabetes, improved immunization procedures, and in developing bioassays for informational macromolecules are considered. In addition, a new approach for externally controlling release rates of drugs using magnetism has been developed. Until now, drug delivery systems were capable of delivering drugs at either constant or decreasing rates. We sought a system that permitted delivery of increased doses on demand, and achieved this by incorporating magnetic particles and drugs into polymeric matrices. Drug release rates can then be increased by an appropriate application of an external magnetic field. Over a five-day period, the magnetic field was applied ten times and drug release rates increased by up to 100% each time. Initial results indicate that this system does not cause tissue damage.     

The effect of ligand donor atoms on ternary complex stability

Formation constants of mixed ligand complexes of Cu²⁺, Zn²⁺, Ni²⁺, Co²⁺, and Mn²⁺,with cyadine-5′-monophosphoric acid (CMP) and various primary ligands such as 1,10-phenanthroline(phen), glycylglycine(glygly) and salicylic acid (sal) have been determined in aqueous solution at 35°C and 0.1 M (KNO₃) by potentiomeric measurements. The acid dissociation constants of all the above mentioned ligands together with their 1 : 1 binary metal complex formation constants were also measured at 35°C. In general all the 1 : 1 binary complexes follow the Irving-Williams order of stability. Further the binary metal complexes of primary ligands are more stable than their ternary complexes with CMP. For ternary complexes, Δ(log K) values seem to change from positive to highly negative as the coordinating atoms of the primary ligands were varied from N,N to N,O^? to O^?O^?. The higher stability of ternary complexes involving phen is due to its Π-bonding interaction with the above metal ions and the relative decrease in the stability of other ternary systems is due to the coulombic repulsion of donor oxygen atoms of primary and secondary ligands. Thus for ternary complexes the stabilities follow a decreasing order of M-phen-CMP > M-glygly-CMP > M-sal-CMP.     

Synthesis and NMR spectra of 2,2,2-trideuterioethylarsine and 2,2,2-trideuterioethylcyclopentaarsine

Pentakis(2,2,2-trideuterioethyl)cyclopentaarsine (PDECA) was synthesized by the reaction of 2,2,2-trideuterioethylarsine with dibenzylmercury. Variable temperature NMR spectra in C₆D₆ are interpreted in terms of fast pseudorotation. NMR and mass spectra and synthesis of 2,2,2-trideuterioethylarsine are also described.     

The behaviour of an electrochemical detector used in liquid chromatography and continuous flow voltammetry: Part III. Potential dependent current

The potential dependence of the steady-state current at a channel electrode has been calculated approximately. Six regions of behavior can be described from a consideration of the characteristic times of diffusion, fluid flow and electrochemical reaction. Wave shapes and half-wave potential shifts are as expected for amperometric cells under all values of the heterogeneous reaction rate constant, and for reversible electrochemical reactions in a coulometric cell. The wave adopts a peculiar shape for irreversible reactions at a coulometric electrode. This is caused by the inapplicability of the concept of mass transfer control in these systems.     

Kinetische und mechanistische untersuchungen von Übergangsmetall-komplex-reaktionen : III. Abhängigkeit des gleichgewichts der addition von tributylphosphan an pentacarbonyl(arylmethoxycarben)wolfram vom substituenten am ring

The reaction of pentacarbonyl(arylmethoxycarbene)tungsten, (CO)₅W[C(OCH₃(p-C₆H₄R)] [R = OCH₃ (a), CH₃ (b), H (c), Br (d), CF₃ (e)], with tributylphosphane at low temperatures results in a reversible addition of the phosphane to the carbene carbon atom. The addition—dissoziation equilibrium is not only dependent on the temperature but also to a strong degree on the nature of the substituent R. ΔG, ΔH and the equilibrium constant K increase in the series from R = OCH₃ to R = CF₃. With the exception of R = OCH₃ the substituents b to e form an isentropic class. For all substituents (a to e) a linear dependency from Jaffés σ-constants was observed for ΔH. Good linear correlation for the substituents b to e was also found for log K and σ as well as for log K and the CO-force constants k_cis and k_trans.     

The reaction of the cyclooctatetraenyl dianion and chlorotrimethylsilane; synthesis and decomposition studies of 5,8-bis(trimethylsilyl)cyclooctatriene

On the basis of PMR decoupling experiments and thermal decomposition studies, the reaction of the cyclooctatetraenyl dianion and chlorotrimethylsilane produces 5,8-bis(trimethylsilyl)-l,3,6-cyclooctatriene, in contrast to a previous report which suggested 7,8-bis(trimethylsilyl)-l,3,5-cyclooctatriene. The product is stable at room temperature in vacuo but undergoes decomposition (isomerization) reactions at higher temperatures or in contact with air.     

Über die bestimmung von isomerisierungsenthalpien und -entropien mit der IR-intensitätsmethode

Among the many sources of error which may affect the results for the enthalpy ΔH and entropy ΔS of isomerization determined by the IR-intensity method, the influence of the temperature dependence of the absorptivities of the reference bands, α_g(T) and α_t(T), is studied theoretically. Based on the general case I, the following three special cases II–IV are examined, in which increasingly stronger constraints are imposed on the compound-specific functions α_g(T) and α_T(T): II. Constant ratio α_g(T)/α_T(T), III. α_g(T) and α_T(T) both temperature independent and different, IV. α_g(T) and α_T(T) both temperature independent and equal. For each case the formulae for the evaluation of ΔH and ΔS as well as the kind and the number of the quantities to be measured are given. Moreover, in the cases I and II new methods for the analysis of the measured data are suggested. In each case the plots of the normalized band intensities $\text{A}{}_{\mathrm{g}}$ and $\text{A}{}_{\mathrm{t}}$ and the temperature T versus each other in different two-dimensional diagrams have been examined to find out whether one of the simpler special cases is applicable for the respective pair of reference bands. It is shown that these plots are not a suitable tool because of the relatively poor accuracy and reproducibility of measured IR-band intensities obtainable up to now.     

Metal complexes of schiff's base derived from salicoylhydrazine and biacetylmonoxime

Biacetylmonoxime-salicoylhydrazone (BMSH) complexes of the types [Hg(BMSH)Cl₂] and [M(BMSH-H)₂], where M = Cu(II), Co(II), Ni(III), Mn(II), Zn(II), Cd(II) and UO₂(VI), have been prepared and characterized by conventional chemical and physical measurements. The IR spectra show that the ligand usually coordinates via carbonyl oxygen (CO), azomethine nitrogen (CNl) and phenolic OH with replacement of hydrogen by metal ions but acts as a bidentate molecule coordinating through (CO) and (CNl) in the Hg(II) complex. The magnetic and spectral data of the Co(II) and Ni(II) complexes support octahedral stereochemistry, whilst tetragonally distorted octahedral geometry is suggested for the Cu(II) complex.     

Resonance Raman spectra of 15N enriched metallooctaethylorphyrins. Characterization of the oxidation state marker bands of hemoproteins

Resonance Raman spectra of ¹⁵N enriched metallooctaethylporphyrins [M(OEP) ? ¹⁵N₄] [M = Ni²⁺, Fe³⁺ (high spin), and Fe³⁺ (low spin)] were observed. Polarized Raman lines corresponding to the oxidation state marker band of hemoproteins were observed at 1377 (Ni), 1369 (Fe high spin) and 1372^?1 (Fe low spin) which were shifted to lower frequency from those of the ¹⁴N compounds by 6, 5, and 6 cm^?1, respectively. The vibrational mode for this band was shown to include an appreciable contribution of the C_αN symmetric stretching vibration and to be associated with ca. 0.01 Å of in-phase displacement of the four pyrrole nitrogens toward the metal ion.     

An unusual reaction of terramycin with methyl iodide

An unusual fragmentation reaction was observed when terramycin is treated with MeI in acetone at room temp. The reaction proceeds with quaternization, loss of trimethylamine, fission of bonds 4a,5 and 12,12a with formation of an aldehydo-lactone derived from rings B, C and D. Additionally some transformations of this lactone are described.     

Metall-π-komplexe von benzolderivaten : III. Bis(diphenylphosphino-h6-benzol)-chrom(0)

Rhodium complexes containing poly(pyrazolyl)borate ligands are described, and the fluxional nature of some of them considered.     

Mean-square amplitudes of vibration and shrinkage effects from mindo/2 calculations

MINDO/2 semi-empirical molecular orbital theory can be used to calculate mean-square amplitudes of vibration and shrinkage effects. Calculated values for ethylene and benzene deviate from spectroscopic values by an average of 4 %. The force field calculations can be carried out conveniently in Cartesian coordinates.