The reaction mechanisms of boron amidinate and small molecules: a density function theory study

Density functional theory calculations have been carried out to explore the reaction mechanisms for the reactions of “frustrated Lewis pairs” (FLPs) with small molecules. Four reactions were studied in the present investigation. A new N-heterocyclic carbene borane, boron amidinate compound HC(iPrN)₂B(C₆F₅)₂ (1), classified as FLPs, was chosen as the common reactant of these reactions. It was used to react with CO₂, CO, and two terminal alkynes, methylacetylene and phenylacetylene. The reactions of 1 with CO₂ and CO can both be regarded as the concerted addition mechanisms. In these reactions, the formations of the C2–N2 and B–O1 bonds take place simultaneously. For the reactions of 1 and methylacetylene or phenylacetylene, our calculations indicated that a deprotonation pathway and the connection between B atoms and terminal alkyne C atoms occur by a concerted manner simultaneously, together with the connection between N2 and hydrogen atoms. We also investigated the reaction mechanisms according to the frontier molecular orbital (FMO) theory and carried out electric charge analyses, finding that the two results were consistent with each other perfectly. Electric charges transfer from HOMO of 1_OPEN to LUMO of CO₂ or CO. In contrast, electric charges transfer from HOMO of methylacetylene or phenylacetylene to LUMO of 1_OPEN.     

Chemistry of fluorinated quinones I. The Diels-Alder reactions of fluoranil

The Diels-Alder reaction of fluoranil with cyclopentadiene, 1,3-butadiene, and 1-acetoxy-1,3-butadiene gave 1,4, 5, 8-bis(methylene)-4a, 8a, 9a, 10a-tetrafluoro-1, 4, 4a, 5, 8, 8a, 9a, 10a-octahydroanthraquinone (I), 2, 3, 4a, 8a-tetrafluoro-4a, 5, 8, 8a-tetrahydro-1,4-naphthoquinone (III), and 5-acetoxy-2, 3, 4a, 8a-tetrafluoro-4a, 5, 8, 8a-tetrahydro-1,4- naphthoquinone (VI), respectively. Hydrogenation of I gave the expected saturated diketone(II). Hydrogenation of III afforded, with elimination of the two tertiary fluorines, 2,3-difluoro-5, 6, 7, 8-tetrahydro-1, 4- dihydroxynaphthalene (IV). In hydrogenation of VI, acetic acid and two moles of hydrogen fluoride were eliminated to give 2,3-difluoro-1, 4-dihydroxynaphthalene(VII). Both dihydroxy compounds IV and VII yielded on oxidation with ferric chloride the corresponding quinones, 2, 3- difluoro-5, 6, 7, 8-tetrahydro-1, 4-naphthoquinone (V) and 2, 3-difluoro-1, 4-naphthoquinone (VIII), respectively. Equivalent amounts of compounds IV and V gave a red-brown semiquinone IX, and a mixture of VI and VIII gave a dark-violet semiquinone X.     

Benzopyranopyridine derivatives 3. Reaction of 1-azaxanthone with grignard reagents

Three different classes of compounds were isolated in the reaction of Grignard reagents with 5-H[1]benzopyrano[2,3-b]pyridin-5-one, commonly called 1-azaxanthone. The formation of (a) 4-substituted 1,4-dihydro-1-azaxanthones (II), (b) 5-substituted-5-hydroxy-1-azaxanthenes (III) or (c) 4,5-disubstituted-1-azaxanthenes (IV) is dependent on the solvent used in the preparation of the Griganrd reagent (i.e. ether or tetrahydrofuran), the steric properties of the reagent and on the temperature. The isolated compounds were characterized by chemical derivatives and/or spectroscopic analyses.     

New processable polyaromatic amides curable by Diels-Alder cycloaddition

New processable polyaromatic amides were prepared from the acid chloride of bis-m-carboxyphenyl acetylene (V), the acid chloride of 1,4-bis-m-carboxyphenyl-1,3-butadiene (VI), and several aromatic diamines. The polyamides that contained acetylene units were cured by Diels-Alder cycloaddition reaction with 1,4-diphenyl-1,3-butadiene, whereas the polyamides with 1,3-butadiene units were cured with N-phenyl maleimide. Cured polyamides showed an increase in t_g, thermal, and heat stabilities. The polyamides can be cast into films and produce good glass-fiber laminates.     

Synthesis of nanostructures based on 1,4- and 1,3,5-phenylethynyl units with π-extended conjugation. Carbon networks dendrimer base units

A convenient and efficient synthesis of 3,5-di(silylethynyl)phenylacetylene and p-[3,5-di(silylethynyl)phenylethynyl]phenylacetylene has been carried out. These compounds serve to prepare nanometer-sized conjugated 1,4- and 1,3,5-phenylethynyl oligomers, by means of cross-coupling with a convenient haloaryl derivative, catalysed by palladium(II), in excellent yields. The phenylethynyl homologues show fluorescence emission, the wavelength of which is displaced by approximately 20 nm by each phenylethynyl unit increasing the conjugate chain.     

Beiträge zur Organolanthanidchemie. III [1]. Darstellung und Eigenschaften von 1,4-Diaryl-1,3-butadien-Komplexen der Lanthanide

Contributions to Organolanthanide Chemistry. III. Synthesis and Properties of 1,4-Diaryl-1,3-butadiene Lanthanide Complexes Cyclopentadienyllanthanide halides react with 1,4-diarylbutadienes in the presence of alkali metals to give Cp*La(1,4-Ph₂C₄H₄) · DME ( I ), Cp*La(1,4-{o-CH₃O? C₆H₄}₂ · C₄H₄) · 2DME ( II ), [Li(THF)₃][Sm(1,4-Ph₂C₄H₄)₂] ( III ), [Li(DME)][(1,4-{p-CH₃? C₆H₄}₂C₄H₄)LuCl₂] ( IV ) and [Li(DME)][(1,4-{o-CH₃O? C₆H₄}₂C₄H₄)LuCl₂] ( V ). Samariumtrichloride reacts with 1,4-diphenyl-butadiene and lithium in tetrahydrofurane with formation of [Li(THF)₄][Sm(1,4-Ph₂C₄H₄)₂] ( VI ). Reaction of samarium with the p-tolyl derivative in the presence of iodine gives (1,4-{p-CH₃? C₆H₄}₂C₄H₄)SmI · 3THF ( VII ). The compounds were characterized by elementary analysis, i.r., ¹H- and ¹³C- n.m.r., and EI-MS spectra.     

Comparison of catalytic properties of systems based on nickel complexes with 1,4-diaza-1,3-butadiene ligands in reactions of styrene hydrogenation and ethylene polymerization

Turnover frequencies of catalytic systems based on nickel complexes with 1,4-diaza-1,3-butadiene (α-diimine) ligands in the reactions of styrene hydrogenation and ethylene polymerization were determined. Results are presented of a study by the electron paramagnetic resonance method and IR spectroscopy of 1,4-diaza-1,3-butadiene complexes of nickel(II) and anion radicals formed in the interaction of the starting components under the conditions of catalysis. It was shown that the paramagnetic Ni(I) complexes are precursors of complexes catalytically active in the hydrogenation and polymerization reactions.     

Synthesis,characterization and catalytic studies of iron(III), cobalt(II), nickel(II) and copper(II) complexes containing triphenylphosphine and β-diketones

A series of new β-diketonato complexes have been synthesized from the reactions of iron(III), cobalt(II), nickel(II) and copper(II) Ph₃P complexes with β-diketones (acetylacetone, benzoylacetone and dibenzoylmethane). All the complexes have been characterized by elemental analyses, spectral studies (i.r., electronic., magnetic., e.p.r., ¹H-n.m.r.) and cyclic voltammetry. The new complexes have been used as catalysts for aromatic coupling and oxidation reactions. Higher catalytic activity has been observed for the nickel(II) complexes compared to the other complexes.     

Catalytic action of metallic salts in autoxidation and polymerization. VIII. Polymerization of methyl methacrylate by various metal acetylacetonate–cyclic ether hydroperoxides

Polymerization of methyl methacrylate by cyclic ether hydroperoxide–metal acetylacetonate systems for a number of different metals was carried out to compare with the tert-butyl hydroperoxide–metal acetylacetonate initiating systems. The rate of polymerization of methyl methacrylate with cyclic ether hydroperoxides as initiating systems was much higher than that with tert-butyl hydroperoxide. In cyclic ether hydroperoxide initiating systems, V(III), Co(II,III), Fe(III), Cu(II), and Mn(II) promoted the polymerization rate markedly, and Zn(II), Ni(II), Al(III), and Mg(II) had little or no effect; in the tert-butyl hydroperoxide initiating system only V(III), Co(II), and Mn(II) enhanced polymerization rate, and most of other metals showed little or no effect. Furthermore, noticeable differences in color of solution and appearance during polymerization, and in relation between conversion and the degree of polymerization were observed. The effect of metal acetylacetonates on hydroperoxide initiators in polymerization of methyl methacrylate was also compared with that on the decomposition of hydroperoxides.     

Transition metal ion complexes of thiosemicarbazones derived from 2-acetylpyridine. Part 3. The 3-hexamethyleneimine derivative

Summary Metal ion complexes of the thiosemicarbazone, 3-hexamethyleneimine-3-thiocarboxylic acid-2-[1-(2-pyridyl)-ethylidene]hydrazide (HLhexim) have been prepared and spectrally characterized. HLhexim coordinates primarily as the deprotonated tridentate ligand (i.e., pyridylN, azomethineN, and thione sulphur). The air oxidised cobalt(III) complex, [Co(LHexim)₂] (BF₄), was isolated from the preparation with cobalt(II) tetrafluoroborate, but other cobalt(II) salts yielded tetrahedral cobalt(II) compounds. Planar nickel(II) and copper(II) complexes were isolated from preparations with halide salts. Significant differences in the spectral properties of the various complexes are observed when compared to other thiosemicarbazones prepared from 2-acetylpyridine.     

Transition metal ion complexes of thiosemicarbazones derived from 2-acetylpyridine. Part 1. The4N-methyl derivative

Summary A series of metal ion complexes of the thiosemicarbazone,N-methyl-2[1-(2-pyridinyl)ethylidene]-hydrazinecarbothioamide (HL4M) has been prepared and spectrally characterized. HL4M coordinates either as a neutral bidentate ligand (i.e., pyridyl N and imine N) or as deprotonated tridentate ligand (i.e., pyridyl N, imine N and thiol sulphur). The cobalt(II) salts yield hexacoordinated cobalt(III) cations, and an isoelectronic species, [Ni(L4M)₂], has been formed from Ni(C₂H₃O₂)₂. The remaining nickel(II) complexes involve the neutral ligand, as do two of the three copper(II) complexes. HL4M possesses a weaker ligand field and has less covalency in its bonding than related thiosemicarbazones that possess anN-dialkyl-function.     

Atom-sparing synthesis of tertiary diphosphine dichalcogenides from acetylenes and secondary phosphine chalcogenides

Secondary phosphine oxides and phosphine sulfides react with acetylene, methylacetylene, and phenylacetylene in the presence of strong bases (KOH-DMSO, KOH-THF) by the mechanism of double nucleophilic α,β-addition to form tertiary diphosphine dioxides and diphosphine disulfides in high yield (up to 97%).     

Metallacycloalkanes : II. Reactions of α,α′-bipyridyl-5-nickela-3,3,7,7-tetramethyl-trans-tricyclo[4.1.0.02,4]heptane

The title compound (II) underwent reductive elimination on treatment with maleic anhydride, tetracyanoethylene or triphenylphosphite to give 3,3,6,6,-tetramethyl-trans-tricyclo[3.1.0.0^2,4]hexane (III). With triphenylphosphite bi(2,2-dimethylcyclopropyl) (V) and 1-(2,2-dimethylcyclopropyl)-3-methyl-1,3-butadiene (VI) were also formed. Acidolysis of II with either HCl, malonic acid or methanol gave V. An intermediate complex α,α′-bipyridyl(phenoxy)-3-nickel-1,1′-bi-(2,2′-dimethylcyclopropyl) (VIII) was isolated by reaction of II with phenol. Methylene dibromide reacts with II to give III and 3,3,7,7-tetramethyl-trans-tricyclo[4.1.0.0^2,4]heptane (IV). With triethylaluminum and II complete exchange of the alkyl groups occurred and V was released on hydrolysis. Trifluoroborane diethyl ether and II gave 3,3,6,6-tetramethylcyclohexa-1,4-diene in a rearrangement-displacement reaction. The cyclodimerisation of 3,3-dimethylcyclopropene (I) to III catalysed by II and the fact that II can be recovered from the reaction mixture provides strong evidence for the intermediacy of metallacyclopentanes in these transition-metal-catalysed [2π + 2π] cyclo-additions.     

Addition of 1,2-dibromo-1-chlorotrifluoroethane to chlorotrifluoroethylene induced by uv-radiation. Synthesis of perfluoro-1,3-butadiene and perfluoro-1,3,5-hexatriene

Photochemically initiated reaction of 1,2-dibromo-1-chlorotrifluoroethane (II) with chlorotrifluoroethylene (I) gave 38% 1,4-dibromo-2,3-dichlorohexafluorobutane (III) and 19% 1,6-dibromo-2,3,5-trichlorononafluorohexane (IV) in addition to the higher telomers. Dehalogenations of III and IV yielded perfluoro-1,3-butadiene (VI) and perfluoro-1,3,5-hexatriene (VIII) with 3-chlorononafluoro-1,5-hexadiene (VII), respectively. Photochemical reduction of butane III with 2-propanol resulted in a preferential reduction of CBr bonds, and from 2,3-dichloro-1,1,2,3,4,4-hexafluorobutane (IX) thus formed, esters of difluoroacetic acid were prepared by dehalogenation of IX and subsequent oxidation and esterification of the product. The photochemical reduction of hexane IV gave a mixture of 79% trichlorononafluorohexane XII and 21% dichlorononafluorohexane XIII. The mechanism of formation of the unusual products of the title addition reaction is discussed.     

Polymerization by transition metal derivatives. XII. Factors controlling activity and stereospecificity in the 1,4 polymerization of butadiene by monometallic nickel catalysts

In the course of investigations of polymerization of diolefins by transition metal derivatives, we have synthesized various monometallic nickel coordination catalysts. The complexes were prepared by reacting 2,6,10-dodecatriene-1,12-diyl nickel with protonic acids; they were shown to initiate the stereospecific polymerization of 1,3-butadiene. The study of these catalysts showed the strong influence of the nature of the counteranion used on the stereospecificity and the polymerization rate. Moreover, by adding various ligands, we were able to modify the behavior of the catalytic systems and to prepare either pure cis-1,4 or pure trans-1,4 or cis–trans equibinary polybutadienes, starting from the same complex and keeping a high 1,4 specificity. Some of these modifications were shown to be reversible.     

A new selective and high affinity polymeric complexing agent for transition metal ions

Summary The synthesis and characteristics of a new chelating glycinohydroxamate-containing polymer resin is described. The functionality of the polymer is 1.76 mmolg^–1. The hydrogen capacity, water regain and adsorption capacities for iron(III), cadmium(II), cobalt(II), copper(II), nickel(II) and zinc(II) were measured at various pH values; uptake of the metal ions increased with pH and was quantitative above pH 3 for most of the metal ions. All cations studied showed high exchange rates towards the resin. The half saturation times for iron(III), cadmium(II), copper(II) and zinc(II) were all less than 1 min. The coordination behaviour of the resin was studied with the help of e.p.r., i.r., u.v. and potentiometry. The pK _a of the resin is 10.70 and the log value of the stability constants for iron(III), copper(II), lead(II), zinc(II), cobalt(II), manganese(II), cadmium(II) and nickel(II) were measured as 21.81, 19.50, 19.20, 18.59, 18.51, 18.46, 18.37 and 18.36, respectively, at 25 ° C and I = 0.2M KCl.     

Synthesis,magnetic and spectral studies of iron(III) and cobalt(II,III) complexes of 4-formylantipyrine N(4)-substituted thiosemicarbazones

The synthesis and characterization of complexes of iron(III), cobalt(II) and cobalt(III) with 4-formylantipyrine N(4)-methyl-, N(4)-dimethyl-, and 3-piperidylthiosemicarbazones are reported. Elemental analyses, molar conductivities, magnetic measurements and spectral (i.r., electronic and e.s.r.) studies have been used to elucidate the nature of the metal complexes. The i.r. spectra show that the thiosemicarbazones behave as bidentate or tridentate ligands, either in the thione or thiolato form. Different stereochemistries are proposed for the various cobalt(II) complexes on the basis of spectral and magnetic studies. This revised version was published online in June 2006 with corrections to the Cover Date.     

An Asymmetric Anion‐Pillared Metal–Organic Framework as a Multisite Adsorbent Enables Simultaneous Removal of Propyne and Propadiene from Propylene

The one‐step removal of multi‐component gases based on a single material will significantly improve the efficiency of separation processes but it is challenging, owing to the difficulty to precisely fabricate porous materials with multiple binding sites tailored for different guest molecules. Now a niobium oxide–fluoride anion‐pillared interpenetrated material ZU‐62 (NbOFFIVE‐2‐Cu‐i, NbOFFIVE=NbOF₅^2?) is presented. It features asymmetric O/F node coordination for the simultaneous removal of trace propyne and propadiene from propylene. The narrow distribution nanospace (aperture of Site I 6.75 Å, Site II 6.94 Å, Site III 7.20 Å) derived from the special coordination geometry within ZU‐62 customized the corresponding energy‐favorable binding sites for the propyne and propadiene that enable propadiene uptake (1.74 mmol g^?1) as well as excellent propyne uptake (1.87 mmol g^?1) under ultra‐low pressure (5000 ppm). The multisite capture mechanism was revealed by modeling studies.     

Organic vapor triggered repeatable on-off crystalline-state luminescence switching

A nonporous crystalline solid consisting of an organoarsenic platinum(II) complex, i.e., a mononuclear diiodoplatinum(II) complex trans-PtI(2)(cis-DHDAtBu)(2) (1) with cis-1,4-dihydro-1,4-dimethyl-2,3,5,6-tetrakis(tert-butoxycarbonyl)-1,4-diarsinine (cis-DHDAtBu), shows on-off solid-state luminescence switching through reversible solvent vapor uptake and escape. The on-off switching of solid-state luminescence was achieved without changing the structure or electronic state of the organoarsenic platinum(II) complex.