Elaboration of rac‐Like Active Species from Lewis Base Functionalized Unbridged Zirconocenes for Isospecific Propylene Polymerization

A series of ortho or meta Lewis base functionalized unbridged zirconocenes, [{1‐(E_n‐Ph)‐3,4‐Me₂C₅H₂}₂ZrCl₂] (E=NMe₂, OMe; n=1, 2), and a half‐functionalized zirconocene, [{1‐(p‐Me₂NC₆H₄)‐3,4‐Me₂C₅H₂}{1‐(p‐tolyl)‐3,4‐Me₂C₅H₂}ZrCl₂], were prepared. The crystal structures of these compounds determined by X‐ray diffraction revealed the presence of only C₂‐symmetric rac‐like isomers in the asymmetric units. In combination with methylaluminoxane (MAO) cocatalyst, the meta‐functionalized complexes afforded mixtures of polymers that exhibit multimelting transition temperatures and broad molecular‐weight distributions (MWDs) in propylene polymerization at atmospheric monomer pressure, whereas the ortho‐functionalized complexes did not give rise to polymerization. Stepwise solvent extraction of the polymer mixtures showed that the polymers consist of amorphous, moderately isotactic, and highly isotactic portions, the weight ratio of which is dependent on the reaction temperature. ¹³C NMR spectral analysis indicated that the [mmmm] methyl pentad value of the isotactic portion reached around 90 %. Among the meta‐functionalized zirconocenes, the di‐OMe‐substituted one afforded the largest amount of the isotactic portion at all temperatures, and the portion comprised 82 wt % of the crude polymer obtained at 25 °C. In contrast, propylene polymerization with the half‐functionalized unbridged zirconocene resulted in the formation of nearly atactic polypropylene with a narrow MWD of around 2. These results corroborate the proposition that the rigid rac‐like cation–anion ion pair of type [rac‐L₂ZrP]⁺[Me‐MAO]^? generated in situ, through Lewis acid–base interactions between the functional groups and [Me‐MAO]^?, is responsible for the isospecific propylene polymerization with the given class of functionalized unbridged zirconocenes and further indicate that the formation of such ion pairs can be favored by difunctionalization at the meta position of the phenyl ring with OMe groups.     

An expedient one-pot synthesis of benzophenone Schiff bases from benzene

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Amine Exchange Reactions in Ionic Liquid

An operationally simple, inexpensive, efficient, and environmentally friendly protocol for the amine exchange reactions of 3-N,N-dimethylaminopropiophenone and N,N-dimethylaminomethylferrocene with primary aryl amines is developed using the ionic liquid [bmim]PF ₆ as a solvent. The recovered ionic liquid can be reused for several cycles with constant activity.     

Study of Enol-Keto Tautomerism of N-(2-Hydroxy-1-Naphthylidene)anils

The enol-keto tautomerism of N-(2-hydroxy-1-naphthylidene)anilines was studied. In response to the action of salts (e.g. CaCl₂), in ethanolic solution the equilibrium is shifted extensively in the direction of the keto form; this allows determination of the concentration of the keto form and of the equilibrium constant of the process. In accordance with the Hammett equation, the equilibrium constant varies as a function of the constants a of the substituents on the aniline ring.     

FT-Far Infrared Study of Complexes Involving Schiff Bases and Phenols

Abstract

Long range inter—ring “zig—zag” coupling between C-4 and H-8 (J₄₈ ?1.5 to ?1.8 Hz) has been observed in some 2,4? and 2,3,4? haloquinolines at 75 MHz. The coupling is influenced by the 4-halo substituent.     

Functional data analysis for cash flow and transactions intensity continuous-time prediction using Hilbert-valued autoregressive processes

In this paper we use a functional autoregressive model as a robust predictor of the cash flow and intensity of transactions in a credit card payment systems. Intraday economic time series are treated as random continuous functions projected onto low dimensional subspace. Wavelet bases are considered for data smoothing. We compare two linear wavelet methods for the prediction problem of a continuous-time stochastic process on an entire time interval. Ex poste prediction is used to check the models.     

Hypercomplex derivative bases of polynomials in Clifford analysis

Convergence properties of hypercomplex derivative bases of special monogenic polynomials are studied. These new results extend and improve a lot of known works from the complex case to Clifford setting. Copyright © 2009 John Wiley & Sons, Ltd.