Sequential Addition Reactions Research Articles

Experimental and Theoretical Studies of Nb6C70/+

Nb6C7+ is studied using a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer coupled to a compact supersonic source. Its reactions with H2O, NH3, CH3OH, CH3CN, and C6H6 are reported. For each of these ligands, sequential attachment reactions occur leading to the initial truncation products Nb6C7L4+. Minor amounts of Nb6C7L5+ and Nb6C7L6+ are observed for polar molecules, but they grow in slowly. A measurement of the relative rate constants for the sequential addition reactions of CH3OH, for example, demonstrates quantitatively that addition of the fifth CH3OH is very slow compared to the first four additions. Multiple excitation collisional activation (MECA) on Nb6C7+ yields Nb5C6+, and MECA on Nb5C6+ yields Nb4C4+ as predominant products. Nb6C7+ undergoes iodine abstraction from one CH3I molecule to yield the truncation product, Nb6C7I+. Ab initio Hartree−Fock calculations of Nb6C7 suggest a structure consisting of two cubes with one carbon at the exact inversion center of the D2h symmet...

Structure and Reactivity of C2 Species on Polymetallic Systems

Abstract A variety of polymetallic C2 (C2 and C2H) complexes are prepared by structure expansion of parent metal acetylide complexes, Fp*–C≡C–H (1) and Fp*–C≡C–Fp* (2) [Fp* = (η5–C5Me5)Fe(CO)2], and their structure and reactivity have been investigated as models for surface-bound C2 species formed during catalytic CO hydrogenation. The results summarized here involve (1) intramolecular 1,2-H shift of the C2H complexes relevant to the 1-alkyne-to-vinylidene rearrangement within a metal coordination sphere, (2) electronic influence of metal centers on the structure of dinuclear bridging alkynyl complexes, (3) conversion of the C2 moiety into various C2 functional groups, and (4) synthesis of higher nuclearity dicarbide (C2) cluster compounds with novel coordination structure by sequential addition reactions of metal fragments and direct coupling of a preformed low-nuclearity cluster structure.

ChemInform Abstract: Stereoselective Construction of Functionalized Bicyclic Carbocycles Through Metal‐Halogen Exchange‐Initiated Sequential Conjugate Addition Reactions.

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Stereoselective construction of functionalized bicyclic carbocycles through metal-halogen exchange-initiated sequential conjugate addition reactions

Rapid metal-halogen exchange reactions have been used to initiate the stereoselective formation of transbicyclo[4.3.0]nonane and strained trans-bicyclo[3.3.0]octane derivatives through sequential intramolecular conjugate addition reactions. Stereoselectivity has been controlled in anionic olefin addition reactions as well as in corresponding radical cyclizations through control of acceptor olefin stereochemistry.

Laser‐Induced Addition Reactions of Iodine with Acetylene

AbstractLaser‐induced addition reactions of iodine with acetylene at 5145 and 4880 Å excitation wavelengths are studied, while trans‐1,2‐diiodoethylene is identified as the exclusive reaction product. A sequential addition reaction mechanism initiated by iodine atoms from the direct photodissociation process or collisional induced dissociation can be inferred.

Activation and detoxication of aminophenols. III. Synthesis and structural elucidation of various glutathione addition products to 1,4-benzoquinone

1. Four thioethers of 1,4-hydroquinone with glutathione (GSH) were prepared from 1,4-benzoquinone and characterized by 1H-n.m.r. and partly by 13C-n.m.r. spectroscopy. The structures of three additional thioethers were tentatively assigned by u.v. spectroscopy. 2. The corresponding thioethers of 1,4-benzoquinone with GSH were obtained by oxidation of the corresponding 1,4-hydroquinone thioadducts with PbO2 or potassium ferricyanide. 3. Relative redox potentials of the hydroquinone/benzoquinone thioethers were estimated by determination of their redox equilibria with benzoquinone/hydroquinone. The redox potential of the mono-substituted derivative was 30 mV lower, and that of the di-substituted derivatives 70 mV lower, than that of the unsubstituted couple, thus explaining the readiness of sequential oxidation and addition reactions of the produced thioethers. 4. By use of 1,4-[U-14C]benzoquinone the reaction products with GSH were quantified to elucidate the product orientation. As observed with 1,4-benzoquinoneimine and its thioethers, formation of GSSG was not detected at physiological pH. 5. The high susceptibility of particular thioethers of 1,4-hydroquinone towards (aut)oxidation characterizes these products as reactive intermediates rather than as definitive detoxication products.

Gas-phase measurements of the kinetics of BF2+-induced polymerization of olefinic monomers

The initial steps in the BF2+-induced polymerization of the monomers of ethylene, propylene, cis-2-butene, isobutene, and styrene have been observed in the gas phase at room temperature using the Selected-Ion Flow Tube (SIFT) technique. Rate constants and product distributions have been determined for the initiation of the polymerization in each case. All five initiation reactions were found to be rapid (k ≥ 5.0 × 10−10 cm3 molecule−1 s−1). The primary product ions that propagate polymerization have been identified and sequential addition reactions have been followed in all five systems. For ethylene the energetics of the initial steps have been followed using abinitio molecular orbital theory. Reactions of BF2+ with the vapours of water and benzene have also been characterized. Keywords: ion-induced polymerization, alkenes, kinetics, gas phase ion chemistry.

Stepwise reduction of acetonitrile in [Tp'(CO)(PhC.tplbond.CMe)W(N.tplbond.CCH3)][BF4

We report stepwise reduction of coordinated acetonitrile by sequential hydride and proton addition reactions. Intermediate metal complexes have been isolated and characterized at each stage of the reduction

The IR Photochemistry of Organic Compounds. II. The IR Photochemistry of Ethers: The Decomposition Patterns

Abstract The infrared multiple-photon decomposition (IRMPD) of saturated open-chain ethers has been systematically investigated with the intention of establishing their decomposition patterns. The main products in the IRMPD of ethers (1a–f, 2) are H2CO, CO, H2, and lower hydrocarbons. Acetaldehyde is additionally formed in the IRMPD of 1b and 1d, while acetone is formed in the IRMPD of 1d. The observed results are explained on the basis of the decomposition of the highly vibrationally excited ethers produced in the IRMP excitation. The initial process is the homolytic cleavage of a C–O bond to yield the corresponding alkyl and alkoxyl radicals. The alkyl radicals are trapped by Br2. Sequential splitting and addition reactions of the radicals yield primary products with a high internal energy. The primary products also decompose sequentially into stable products, in part. The sequential processes compete with collisional deactivation. Therefore, the branching ratio depends on the internal energy of the radicals and the primary products.

ChemInform Abstract: Insertion of Carbon Monoxide into Transition‐Metal‐Acyl Bonds to Form α‐Ketoacyl Complexes.

AbstractThe CO insertion into the metal acyl bond of the complexes (I) and (IV) is accomplished by a novel oxidation/NO addition reaction sequence according to the scheme.

Some thermodynamic aspects of aggregation phenomena with special reference to micellization

Aggregation phenomena are generally considered in terms of a sequence of addition reactions. The equilibrium distribution of aggregate sizes ( i) is shown to depend on the relative values of the logarithm of the monomer concentration (ln x 1) and the differential of the standard free energy of micellization with respect to aggregation number d(Δ G θ( i)/d i. Depending on the functional form of Δ G θ( i) one obtains equations relating to phase changes with or without nucleation, to flocculation or to micellization. Some detailed calculations are made for micellization, and various theoretical definitions of the CMC are discussed. Preliminary speculations are presented concerning the change in form of Δ G θ( i) needed to account for changes in micelle shape from spherical to cylindrical.