An electron diffraction determination of the molecular structures of silyl- and germyl-manganese pentacarbonyl in the gas phase

The molecular structures of the title compounds have been determined by gas phase electron diffraction methods. The SiMn and GeMn bond lengths are 240.7 ? 0.5 and 248.7 ? 0.2 pm respectively and the CMnC angles in the silyl and germyl cases are 94.5 ± 2° and 97 ± 2° respectively. Comparisons are made with the reported structure of CH₃Mn(CO)₅ and He^I photoelectron spectra of these compounds in an attempt to determine the extent of d → d π-bonding in the SiMn or GeMn bonds.     

Platination of [3-X-7,8-Ph2-7,8-nido-C2B9H8] (X=Et, F): Synthesis and characterisation of slipped and 1,2→1,7 isomerised products

The reaction of the labelled carborane ligand [3-Et-7,8-Ph₂-7,8-nido-C₂B₉H₈]²⁻ with a source of {Pt(PMe₂Ph)₂}²⁺ affords non-isomerised 1,2-Ph₂-3,3-(PMe₂Ph)₂-6-Et-3,1,2-closo-PtC₂B₉H₈ (1). The analogous reaction between [3-F-7,8-Ph₂-7,8-nido-C₂B₉H₈]²⁻ and {Pt(PMe₂Ph)₂}²⁺ yields 1,8-Ph₂-2,2-(PMe₂Ph)₂-4-F-2,1,8-closo-PtC₂B₉H₈ (3). Compound 1 has a heavily slipped structure (Δ 0.72 Å), which to some degree obviates the need for C atom isomerisation. However, that it is a kinetic product of the reaction is evident from the fact that it reverts to isomerised 1,8-Ph₂-2,2-(PMe₂Ph)₂-4-Et-2,1,8-closo-PtC₂B₉H₈ (2) slowly at room temperature but more rapidly with gentle warming. The heteroatom and labelled-B atom positions in the isomerised compounds 2 and 3 may be explained most simply by the rotation of a CB₂ face of an intermediate based on the structure of 1. Compounds 1–3 were characterised by a combination of spectroscopic and crystallographic techniques.     

Fluorescence probes based on 9‐acridyl derivatives of aromatic amines for monitoring free‐radical polymerization

The series of 9‐acridyl derivatives of aromatic amines have been investigated as fluorescent probes for monitoring the progress of free‐radical polymerization. This study on the changes in the fluorescence intensity and spectroscopic shift of specific compounds was carried out during thermally initiated polymerization of methyl methacrylate and photoinitiated polymerization of 2‐ethyl‐2‐(hydroxymethyl)‐1,3‐propanediol triacrylate‐1‐methyl‐2‐pyrrolidonone mixture. The purpose of this investigation was to find a relationship between the changes in the shape and intensity of fluorescent probes and the degree of monomer conversion into a polymer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3481–3488, 2002     

次级键与晶体中锑(III)螯合物配位多面体研究

考虑立体活性孤对电子附近次级键配位原子的贡献, 对文献报道的三十个氨基多羧酸锑(III)螯合物的晶体结构中配位多面体描述进行了全面的修正. 配位多面体的几何构型指定采用了单位球内截多面体的两面角判据及其相关的ANVPDA程序. 所有配位多面体几何构型的修正均得到了键价计算的有力支持.     

The electronic absorption study of imide anion radicals in terms of time dependent density functional theory

The absorption spectra of the N-(2,5-di-tert-butylphenyl) phthalimide (1-), N-(2,5-di-tert-butylphenyl)-1,8-naphthalimide (2-) and N-(2,5-di-tert-butylphenyl)-perylene-3,4-dicarboximide (3-) anion radicals are studied in terms of time dependent density functional theory (TDDFT). For these anion radicals a large number electronic states (from 30 to 60) was found in the visible and near-IR regions (5000-45,000 cm(-1)). In these regions the TD/B3LYP treatment at the 6-1+G* level is shown to reproduce satisfactorily the empirical absorption spectra of all three anion radicals studied. The most apparent discrepancies between purely electronic theory and the experiment could be found in the excitation region corresponding to D0-->D1 transitions in the 2- and 3- molecules. For these species we argue that the structures seen in the lowest energy part of the absorptions of the 2- and 3- species are very likely due to Franck-Condon (FC) activity of the totally symmetric vibrations not studied in this Letter.     

Bis(cyclopentadienyl)titanium complexes of naphthalene-1,8-dithiolates, biphenyl 2,2'-dithiolates, and related ligands

Titanocene 1,8-dithiolato-naphthalene and titanocene 2,2'-dithiolato biphenyl are produced by the reaction of naphtho[1,8-cd]-1,2-dithiole [or the biphenyl] with titanocene dicarbonyl (Ti(II)) in toluene at room temperature. The pro-ligands 2,7-di(tert-butyl)naphtho[1,8-cd]-1,2-dithiole, 5,6-dihydroacenaphtho[5,6-cd]-1,2-dithiole, 4,5-dithioacephenanthrylene, and 13,14-dithiapicene have been used in similar reactions with titanocene dicarbonyl to investigate the effect of steric bulk and of varying the naphthalene backbone on the final complex. The resulting Cp(2)TiS(2)Ar complexes (Ar = naphthalene) have been shown by temperature-dependent (1)H NMR spectroscopy to exist in solution in an envelope conformation with the six-membered TiS(2)C(3) rings undergoing inversion on the NMR time scale while the similar Cp(2)TiS(2)Ar complexes (Ar = biphenyl, binaphthalene) interconvert more rapidly. Titanocene 2,2'-disulfinato biphenyl has been synthesized by the salt elimination reaction of titanocene dichloride (Ti(IV)) and the disodium salt of biphenyl 2,2'-disulfinic acid. Finally, the effect of using pro-ligands where the sulfur atoms have been mono- or di-oxidized has been studied, and an interesting oxygen elimination reaction is observed for the S=O fragments but not for the SO(2) groups. All complexes have been characterized spectroscopically and seven X-ray structures are reported.     

Polymerization by alkaline earth metal compounds—I. Studies on the polymerization of methylmethacrylate by triphenylmethyl metal derivatives and related compounds of calcium,strontium and barium

A series of related organo-alkaline earth metal compounds of formula (Ph₃C)MX(THF)_η, (M = Ca, Sr, Ba; X = Cl: M = Ca, Sr; X = Br: M = Ba; X = CPh₃), has been isolated and characterized using analytical and spectroscopic techniques. The polymerization of methylmethacrylate (MMA) has been studied using these organometallic compounds as initiators. Investigations of the tacticity variations of polymethylmethacrylate (PMMA) produced in 1,2-dimethoxyethane or tetrahydrofuran (THF) at 210 K have shown that the syndiotacticity is higher in the former solvent, decreases with the following changes in initiator composition: Ca > Sr ? Ba; Cl > Br; in THF, it is dependent on the monomer concentration. The molecular weight distributions of the PMMA samples are broad and have distinct bi- or poly-modal features. The polymerization process appears to be anionic in nature but the evidence suggests that more than one type of propagation occurs and mechanistic aspects are discussed. Polymerization of bulk MMA by these same initiators is also reported. The initiators RMX(THF)_n (M = Sr, R = Me, n = 3 or R = Et, n = 2) and (C₃H₅)SrBr(THF)₂ are shown to be inefficient for polymerization of MMA. The glass transition temperatures of a range of PMMA samples of differing tacticity are presented and discussed.     

Nucleation of the β-modification of isotactic polypropylene

The effects of the organic pigments C.I.P. RED 177 and C.I.P. Yellow 83 as nucleating agents on the crystallization of polypropylene were studied by DSC. The anthraquinone pigment exerted a significant effect, resulting in structural modifications with lower melting point, and particularly the -modification. The DSC curves exhibit four transition regions, with the following temperature intervals: I. 415–417 K, II. 423–425 K, III. 430–432 K and IV. 438–439 K. For evaluation of the -nucleation effect of pigments, the ratio (H ₁+H ₂)/(H ₃+H ₄) was suggested.     

Synthesis of α1-(Cbz-aminoalkyl)-α2-(hydroxyalkyl)phosphinic esters

A synthesis of α₁-(Cbz-aminoalkyl)-α₂-(hydroxyalkyl)phosphinic esters was achieved by the 1,2-addition of the appropriate aldehyde to Cbz-protected phosphinic analogues of amino acid esters in the presence of at least three equivalents of trimethylsilyl chloride and NEt₃. The complete deprotection of the product esters could be achieved in one step using 35% HBr in acetic acid.     

A stratospheric chemical reaction controlling climatic change

It has been established from geological studies that change in the atmospheric content of carbon dioxide gas commenced about one hundred million years ago. The likely origin of this change is advanced as being the onset of the Brewer circulation caused by the rise in terrain induced by tectonic plate movement. It is demonstrated that tectonic plate movement can be affected by impacts from external bodies which penetrate the crust of the Earth. The consequences of the change in atmospheric concentration of carbon dioxide are proposed as first, extinctions and reductions in animal numbers, including primates, as a result of changes in body chemistry of these animals and second, a change in the rate of weathering of rocks giving rise to changes in the availability of chemicals such as calcium and potassium which are essential for plant and animal life. This latter change contributing to the extinctions and reductions in animal numbers. It is shown that the change in weathering can account for the rise to dominance of angiosperm plants. It is concluded that there were several simultaneous evolutionary environments on Earth which were a function of altitude which gave rise to a vertical variation in atmospheric content of carbon dioxide. This variation disappeared with rise of terrain and the onset of the Brewer circulation. Such changes are advanced and being much more important than any changes in temperature caused by greenhouse effects since the disappearance of atmospheric variations in carbon dioxide allowed animal migration. It is demonstrated that the conditions of extinction could be reintroduced by human activities.