The alkali cation effect on the 1H NMR chemical shifts of the indenyl carbanion

The complex character of the temperature dependence of the ¹H NMR chemical shifts of indenyl-lithium and -sodium in dimethoxyethane is explained. It is shown that the cation causes a polarisation of the C? H bonds and thus influences the proton shifts of the anion, both directly by its electric field along the bonds (the direct effect) and indirectly via its effect on the π-electron distribution (the indirect effect). The indirect effect is inferred from ¹³C NMR chemical shift data. By subtracting the temperature dependent contribution of the indirect effect from the experimental ¹H data, the direct effect is visualised. It appears that information on ion paris obtained by ¹H and ¹³C NMR on the one hand and optical spectroscopy on the other hand is complementary. Apparently, aggregation of ion pairs does not seriously affect the chemical shift data.     

The nature of the inductive effect of azinyl groups

The induction constants of azinyl groups are factored into two components, a -induction ( _X ) and a field (_F) component. It is shown that the _X constants of azinyl groups can be thought of as sums of contributions from the phenyl group and the endocyclic nitrogen atoms. A satisfactory correlation is found between the _F constants and the size and direction of the dipole moment of the heterocyclic substituents in the framework of the Kirkwood-Westheimer equation.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 672–676, May, 1987.     

The proton exchange reaction between indene and the indenyl anion

The proton exchange reaction between the indenyl carbanion and its parent compound indene has been studied by NMR as a function of temperature. The rate of this bimolecular reaction is very low and has been found to be strongly dependent on the polarity of the solvent. In solvents like dimethoxyethane (? = 7·2) and diglyme the reaction becomes manifest in the NMR spectrum only at elevated temperatures (T > 150°C). In hexamethylphosphortriamide (? = 30) the rate is much greater and line broadening may be observable at room temperature. The reaction in this solvent is characterised by a frequency factor f = 7 × 10⁷ 1 mol^?1 s^?1, an activation enthalpy ΔH ≠ = 9·5 kcal mol^?1 and an entropy of activation ΔS≠ = ?23 e.u. The low reaction rate and its solvent dependence are briefly discussed.     

The origin and nature of the π-electron steric effect

The existence of conformational or steric proximity substituent effects involving π-electrons has been demonstrated in a number of recent reports but the question of whether this effect is due simply to the size of the substituent or to lone pair electrons on the substituent has not been investigated. Relative to this question, pK_a's for an extensive series of 2'- and 4'-substituted-4-aminobiphenyls and for a series of 4'-substituted-2-amino-biphenyls have been determined. The results of this study demonstrate that a π-electron steric effect is operative in the 2'-substituted-4-aminobiphenyls and that it occurs primarily (when possible) via lone pair electron-π electron interactions and not simply via a steric size effect. The pK_a data for the 4'-substituted-2-aminobiphenyls reinforce this conclusion and further demonstrate that 2,4'-resonance is possible in appropriately substituted 2,4'-disubstituted biphenyls. In addition, the relativity of the concept of substituent size and of electron withdrawing or donating character of various groups is illustrated.     

On the role of the indenyl effect in controlling intramolecular hydride transfer in iron carbonyl complexes

Density functional theory reveals multiple pathways for intramolecular hydride transfer in the cyclopentadienyl and indenyl species (η⁵-C₅H₅)Fe(CO)₃H and (η⁵-C₉H₇)Fe(CO)₃H. The ability of the indenyl ligand to undergo facile η⁵- to η³-‘ring slippage’ stabilises the isomer where the hydride is bonded directly to the metal, which opens up a low-energy pathway for hydride transfer from CO to metal.     

On the nature of the anomeric effect

Calculations of the interaction energies of heteroatoms X and Y unshared electron pairs in structures (I) and (II) have been performed for molecules of 2-methoxytetrahydropyran and fluoromethanol, by semi-empirical EHMO and CNDO/2 methods, as well as by classical dipole-dipole approximation. This type of interaction was shown not to be a factor responsible for the stability of the gauche structure (II). The current interpretation that the anomeric effect is an electrostatic interaction of heteroatom unshared electron pairs (the “rabbit ears” effect) is, therefore, groundless.     

The influence of concentration and anion nature on the support effect

The kinetic of decomposition of copper formate, acetate, propionate and butyrate under non-isothermal conditions was studied. The support materials were carborundum and silica and the concentrations of the supported compounds were 15, 20, 25 and 30 mass%. In order to avoid the effects of thermal gradients and dilution, a series of parallel samples of carboxylate/support mixtures with the same concentration were studied. The support effect was estimated by the difference between the isokinetic temperature of the supported, respectively mixted carboxylate series, and is discussed in connection with the precursor concentration and the nature of the carboxylate anion. The suggestion of considering the thermodynamic activation function instead of the Arrhenius parameters for discussion on compensation effect was argued. This revised version was published online in July 2006 with corrections to the Cover Date.     

The nature of clay volatiles and condensates and the effect on their environment

When clays are heated, a mass loss occurs due to the evolution of volatiles. Most of these are water vapour, but in addition minor amounts of a complex assemblage of other species are liberated. The corresponding condensates are colloidal suspensions. The composition of the volatiles and condensates and the release patterns of the gases are reviewed. The nature of the assemblages varies from one clay to another and depends on the thermal regime. Both volatiles and condensates are very reactive. Their reactivity persists even after prolonged storage. They act as acid catalysts in reactions with organic matter and decompose calcite and other carbonates. Condensates were found to etch the surfaces of quartz crystals and to dealuminate and partly destroy an Al-rich faujasite (zeolite). Possible implications of reactions of clay volatiles and condensates for natural processes are discussed.     

The chameleon-like nature of zwitterionic micelles: effect of cation binding

Addition of salts, especially perchlorates, to zwitterionic micelles of SB3-14, C(14)H(29)NMe(2)(+)(CH(2))(3)SO(3)(-), induces anionic character and uptake of H(3)O(+) by SB3-14 micelles. Thus, the addition of alkali metal perchlorates accelerates the acid hydrolysis of 2-(p-heptoxyphenyl)-1,3-dioxolane, HPD, in the presence of SB3-14 micelles, which depends on the local proton concentration at the micelle surface. The addition of metal chlorides to solutions of such perchlorate-modified SB3-14 micelles decreases both the negative zeta potential of the micelles and the observed rate constant for acid hydrolysis of HPD. The effect of the monovalent cations Li(+), Na(+), and K(+) is smaller than that of the divalent cations Be(2+), Mg(2+), and Ca(2+), and much smaller than that of the trivalent cations Al(3+), La(3+), and Er(3+). The major factor responsible for this cation valence dependence of these effects is shown to be electrostatic in nature, reflecting the strong dependence of the micellar surface potential on the cation valence. The fact that the salt effects are not identical after correction for the electrostatic effects indicates that additional secondary nonelectrostatic effects may contribute as well.     

The synthesis and reactivity of some indenyl and bis-indenyl ruthenium carbonyl complexes

The reaction of [Ru₃(CO)₁₂] (1), with indene in refluxing xylene affords [{(η⁵-C₉H₇)Ru(CO)₂}₂] (2), in high yield. An analogous reaction of 1 with 2-phenylindene affords the expected dinuclear complex [{(η⁵-C₉H₆Ph)Ru(CO)₂}₂] (5), and a heptaruthenium cluster [(C₉H₄Ph)Ru₇(μ-H)(μ-CO)₂(CO)₁₆] (6). The indenyl ligand in compound 6 exhibits a novel bonding mode in which the benzenoid ring is μ₄,η¹:η¹:η²:η² bound to the cluster. Refluxing 1 with bis-indenyl methane affords the dinuclear complex [Ru₂(CO)₄{μ-(η⁵-C₉H₆)₂CH₂}] (7), which reacts with iodine via Ru-Ru bond cleavage to give [Ru₂I₂(CO)₄{(η⁵-C₉H₆)₂CH₂}] (8).     

Synthesis and structural characterization of ferrocenyl indenyl derivatives

In this study, four ferrocenyl indenyl derivatives, C₉H₇–C≡C–Fc (1), C₉H₇–C≡C–Ph–Fc (2), C₉H₇–C≡C–Ph–C≡C–Fc (3), and C₉H₇–Ph–C≡C–Fc (4) (where C₉H₇=indenyl; Fc=C₅H₅FeC₅H₄; Ph=C₆H₅), have been synthesized by Sonogashira and Suzuki cross-coupling reactions and characterized by elemental analysis, and FT-IR, ¹H, ¹³C-NMR, and MS spectroscopic methods, respectively. The molecular structures of 1, 2, and 4 were determined by X-ray single crystal diffraction. Two molecules appeared in the crystal structure of 4, and they interact through an intermolecular hydrogen bond. The electrochemical redox potential differences in 1–4 were investigated using cyclic voltammetry and calculations.     

The bridged cyclopentadienyl indenyl (fluorenyl) zirconocene complexes for polyethylene macromonomers

The synthesis of long‐chain branched polyethylene includes the generation of vinyl‐terminated polyethylene macromonomers and the copolymerization of these macromonomers with ethylene. Four new bridged cyclopentadienyl indenyl (fluorenyl) zirconocene complexes 1a–b, 2a–b were prepared and showed high activities for ethylene homopolymerization upon the activation of methylaluminoxane. The steric bulk of bridged substituent has a profound effect on the catalytic activity as well as on the molecular weight of resulting polyethylene. Complex 1b showed the highest activity of up to 5.32 × 10⁶ g PE/(mol Zr h) for ethylene homopolymerization at 70 °C, which was higher than that of Cp₂ZrCl₂. The polyethylenes produced with complexes 1a–d/MAO are mostly vinyl‐terminated, possess low molecular weight and fit as macromonomers. The (p‐MePh)₂C‐bridged cyclopentadienyl indenyl zirconocene complex 1a could produce polyethylene macromonomer with selectivity for the vinyl‐terminal as high as 94.9%. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis and reactivity of mixed-ring indenyl complexes of molybdenocene

The complex [IndCpMo(NCMe)₂][BF₄]₂ provides a suitable entry to the synthesis of IndCpMoBr₂ and IndCpMoMe₂. The latter, also available from IndCpMoX₂ (X = Cl, Br) and MeMgCl, reacts with HCl to give IndCpMoCl(Me) which, in turn reacts with NaSPh to yield IndCpMo(SPh)(Me). Cyclic voltammetry shows that these three alkyl complexes undergo a 1e reversible oxidation to 17 e Mo^V cations. IndCpMoCl(Me) is oxidized by [Cp₂Fe]BF₄ to afford [IndCpMoCl(Me)]BF₄ in 95% yield. Reaction of [IndCpMo(NCMe)₂][BF₄]₂ with KBPz₄ in CH₂Cl₂/NMF leads to [IndCpMo(κ²-BPz₄)]BF₄. Taken together with previous reports these results show that the indenyl ring slows down substitutional chemistry at the fragment (Cp′ = Cp, Ind) by steric reasons, overshadowing any acceleration due to a possible indenyl effect.     

Kinetics of urethane formation from isophorone diisocyanate: The alcohol nature effect

The kinetics of the noncatalytic reactions of isophorone diisocyanate with n-propanol, isopropanol, 1,3-diazidopropan-2-ol, propargyl alcohol, and phenol in toluene in the temperature range from 20 to 90°C at the stoichiometric ratio of reactive groups has been investigated by IR spectroscopy. The apparent rate constants for the reactions of the aliphatic and cycloaliphatic isocyanate groups of isophorone diisocyanate with all of the alcohols have been measured. The activation parameters of the reactions of isophorone diisocyanate with n-propanol, isopropanol, and 1,3-diazidopropan-2-ol have been determined. The data obtained are considered in terms of the alcohol structure and molecular organization of solutions.