Computational study of the EtOH-TiCl4-MgCl2 Ziegler-Natta precatalyst

International audienc

Computational Study of the EtOH-TiCl4-MgCl2 Ziegler-Natta catalyst

International audienc

Atomic-scale study of the Ziegler-Natta catalyst

International audienc

Surface Characterization of supported catalysts: the interplay between modelling and experiments.

International audienc

Quantitative spectra-structure relation for borohydrides

International audienc

Structural study of the Ziegler-Natta catalyst

International audienc

C–H Activation and Proton Transfer Initiate Alkene Metathesis Activity of the Tungsten(IV)–Oxo Complex

International audienceIn alkene metathesis, while group 6 (Mo or W) high-oxidation state alkylidenes are accepted to be key reaction intermediates for both homogeneous and heterogeneous catalysts, it has been proposed that low valent species in their +4 oxidation state can serve as precatalysts. However, the activation mechanism for these latter species—generating alkylidenes—is still an open question. Here, we report the syntheses of tungsten(IV)–oxo bisalkoxide molecular complexes stabilized by pyridine ligands, WO(OR)2py3 (R = CMe(CF3)2 (2a), R = Si(OtBu)3 (2b), and R = C(CF3)3 (2c); py = pyridine), and show that upon activation with B(C6F5)3 they display alkene metathesis activities comparable to W(VI)–oxo alkylidenes. The initiation mechanism is examined by kinetic, isotope labeling and computational studies. Experimental evidence reveals that the presence of an allylic CH group in the alkene reactant is crucial for initiating alkene metathesis. Deuterium labeling of the allylic C–H group shows a primary kinetic isotope effect on the rate of initiation. DFT calculations support the formation of an allyl hydride intermediate via activation of the allylic C–H bond and show that formation of the metallacyclobutane from the allyl “hydride” involves a proton transfer facilitated by the coordination of a Lewis acid (B(C6F5)3) and assisted by a Lewis base (pyridine). This proton transfer step is rate determining and yields the metathesis active species

C–H Activation and Proton Transfer Initiate Alkene Metathesis Activity of the Tungsten(IV)–Oxo Complex

ISSN:0002-7863ISSN:1520-512

Анализ этических проблем банковской отрасли Украины

У статті подано аналіз поточної ситуації в банківській галузі України в контексті етичних стандартів банківського бізнесу. Визначено основні порушення бізнес-етики, як з боку банківських установ, так і з боку вкладників і позичальників банків. Значне місце приділено аналізу об'єктивних і ментальних чинників низької економічної культури населення України.The article analyses current state of Ukrainian banking sphere in terms of improving ethic standards of banking business. Main violations of business ethics on the part of banking institutions, bank depositors and loaners are identified. Significant attention is paid to the analysis of objective and mental factors of low economic culture of Ukrainian population.В статье представлен анализ текущей ситуации в банковской отрасли Украины в контексте этических стандартов банковского бизнеса. Определены основные нарушения бизнес-этики, как со стороны банковских учреждений, так и со стороны вкладчиков и заемщиков банков. Значительное место уделено анализу объективных и ментальных факторов низкой экономической культуры населения Украины