System size and centrality dependence of the balance function in A + A collisions at sqrt s NN = 17.2 GeV

Electric charge correlations were studied for p+p, C+C, Si+Si and centrality selected Pb+Pb collisions at sqrt s_NN = 17.2$ GeV with the NA49 large acceptance detector at the CERN-SPS. In particular, long range pseudo-rapidity correlations of oppositely charged particles were measured using the Balance Function method. The width of the Balance Function decreases with increasing system size and centrality of the reactions. This decrease could be related to an increasing delay of hadronization in central Pb+Pb collisions

System size and centrality dependence of the balance function in A+A collisions at sqrt[sNN]=17.2 GeV

Electric charge correlations were studied for p+p, C+C, Si+Si, and centrality selected Pb+Pb collisions at sqrt[sNN]=17.2 GeV with the NA49 large acceptance detector at the CERN SPS. In particular, long-range pseudorapidity correlations of oppositely charged particles were measured using the balance function method. The width of the balance function decreases with increasing system size and centrality of the reactions. This decrease could be related to an increasing delay of hadronization in central Pb+Pb collisions

Reactivity of silanes in silylation of alkenes and alcohols in the presence of alkali metal trialkylhydroborates

Wydział ChemiiCelem badań stanowiących treść rozprawy doktorskiej było określenie reaktywności wodorosilanów w reakcjach addycji i sprzęgania w układach katalitycznych powstających w obecności trialkilohydroboranów litowców, ze szczególnym uwzględnieniem przemian, jakim mogą one ulegać pod wpływem środowiska reakcji. Na podstawie wyników przeprowadzonych badań ustalono, że trietylohydroboran sodu użyty w układzie reakcyjnym zawierającym kompleks kobaltu(II) jest niezbędny do zajścia reakcji, pełniąc jednak tylko rolę aktywatora. Po drugie, trietylohydroborany sodu, potasu i litu, wobec braku kompleksów metali, same mogą katalizować powstanie produktów hydrosililowania winyloarenów i podobnych związków. Po trzecie, w przypadku, gdy substraty należą do grupy alkoholi, jedyną reakcją jest dehydrogenujące sprzęganie z utworzeniem alkoksysilanów i gazowego wodoru. Wykazano w ten sposób, że trialkilohydroborany litowców, będące częstymi czynnikami aktywującymi układy katalityczne oparte na kompleksach metali przejściowych, w odpowiednich warunkach mogą wywierać bezpośredni wpływ na przebieg reakcji.The aim of the study described in this very thesis was to determine the reactivity of hydrosilanes in the addition and coupling reactions with the aid of catalytic systems formed in the presence of alkali metal trialkylborohydrides, with particular consideration of possible changes induced to the latter by the reaction environment. On the basis of the results of the research carried out, it was first established that in a reaction system containing cobalt(II) complex, the presence of sodium triethylhydroborate is required for any reaction to happen, as it activates the former. Secondly, triethylhydroborates of sodium, potassium, and lithium, in the absence of any metal complex, can themselves catalyse selective formation of Markovnikov-type products of hydrosilylation of vinylarenes and similar compounds. If alcohols are substrates, the only reaction taking place is dehydrogenative coupling with hydrosilanes yielding alkoxysilanes. It has therefore been shown that alkali metal trialkylborohydrides, which are often used as activators of transition-metal-based catalytic systems, under some conditions can exert direct influence on the reaction pathway

Reactivity of silanes in silylation of alkenes and alcohols in the presence of alkali metal trialkylhydroborates

Wydział ChemiiCelem badań stanowiących treść rozprawy doktorskiej było określenie reaktywności wodorosilanów w reakcjach addycji i sprzęgania w układach katalitycznych powstających w obecności trialkilohydroboranów litowców, ze szczególnym uwzględnieniem przemian, jakim mogą one ulegać pod wpływem środowiska reakcji. Na podstawie wyników przeprowadzonych badań ustalono, że trietylohydroboran sodu użyty w układzie reakcyjnym zawierającym kompleks kobaltu(II) jest niezbędny do zajścia reakcji, pełniąc jednak tylko rolę aktywatora. Po drugie, trietylohydroborany sodu, potasu i litu, wobec braku kompleksów metali, same mogą katalizować powstanie produktów hydrosililowania winyloarenów i podobnych związków. Po trzecie, w przypadku, gdy substraty należą do grupy alkoholi, jedyną reakcją jest dehydrogenujące sprzęganie z utworzeniem alkoksysilanów i gazowego wodoru. Wykazano w ten sposób, że trialkilohydroborany litowców, będące częstymi czynnikami aktywującymi układy katalityczne oparte na kompleksach metali przejściowych, w odpowiednich warunkach mogą wywierać bezpośredni wpływ na przebieg reakcji.The aim of the study described in this very thesis was to determine the reactivity of hydrosilanes in the addition and coupling reactions with the aid of catalytic systems formed in the presence of alkali metal trialkylborohydrides, with particular consideration of possible changes induced to the latter by the reaction environment. On the basis of the results of the research carried out, it was first established that in a reaction system containing cobalt(II) complex, the presence of sodium triethylhydroborate is required for any reaction to happen, as it activates the former. Secondly, triethylhydroborates of sodium, potassium, and lithium, in the absence of any metal complex, can themselves catalyse selective formation of Markovnikov-type products of hydrosilylation of vinylarenes and similar compounds. If alcohols are substrates, the only reaction taking place is dehydrogenative coupling with hydrosilanes yielding alkoxysilanes. It has therefore been shown that alkali metal trialkylborohydrides, which are often used as activators of transition-metal-based catalytic systems, under some conditions can exert direct influence on the reaction pathway

Acceleration of alkyne metathesis in multicomponent catalytic systems by use of alternative Mo(0) sources under optimised conditions

Abstract. Alkyne metathesis in multicomponent catalytic systems, although subject to changes, is still a domain of molybdenum hexacarbonyl as a source of Mo(0). Our findings show that this coordination compound is relatively inert under metathesis conditions, which results in noticeably long induction of catalytic activity, and the kinetics of this transformation can greatly benefit from switching to more labile Mo(0) complexes. Several easily obtainable ones had been tested and [Mo(CO)3(py)3] has been chosen as the one exhibiting the most desired features, i.e. nearly instant catalytic activity and relative stability in the air

Silylative coupling : a useful tool for selective organic synthesis

The design and development of highly selective methods for the synthesis of functionalized olefins based on sequential catalytic reactions using organosilicon reagents have been the subject of extensive study because of their versatile application in organic and organometallic synthesis. The ruthenium-catalyzed silylative coupling of olefins with vinyl-substituted organosilicon compounds (discovered by professor Bogdan Marciniec and co-workers in Poznań) represents one of the most efficient methods for the synthesis of stereodefined alkenylsilanes and isomeric bis(silyl)alkenes, which are particularly attractive scaffolds for further transformations including palladium-catalyzed cross-coupling with organic halides (Hiyama coupling) or substitution with organic and inorganic electrophiles. The unique feature of these methodologies is that the stereochemistry of the overall processes can be controlled during the initial step as the subsequent desilylation usually proceeds with retention of the configuration at the carbon atom and allows the formation of stereodefined products. The sequential silylative coupling - Hiyama coupling has been successfully used for stereoselective synthesis of (E)-stilbenes, bis-(E)-styrylarenes, stilbenoid dendrimers and poly(arylene-vinylene)s. On the other hand, the combination of silylative coupling with electrophilic halodesilylation reaction has been applied for the selective preparation of synthetically useful alkenyl halides (e.g. (E)-styryl halides, (E)-N-2-iodovinylcarbazole, (E)-N-2-iodovinylamides) - versatile coupling partners in palladium-catalyzed Suzuki and Sonogashira couplings, leading to vide variety of stereodefined ß-substituted (E)-enimides, (E,E)-dienimides and (E)- enynimides as well as related л-conjugated derivatives of N-substituted carbazole. The discovery of sequential silylative coupling and rhodium- or iridium-catalyzed acylation reactions is of great importance in the synthesis of (E)-α,ß-unsaturated ketones. The article highlights recent developments and covers literature mainly from the last decade in the sequential (also one-pot) synthetic strategies including ruthenium-catalyzed silylative coupling followed by desilylative cross-coupling, acylation and halogenation, leading to stereodefined я-conjugated organic derivatives which are widely applied as fine chemicals, functional materials or building blocks in organic synthesis

Direct Dehydrogenative Coupling of Alcohols with Hydrosilanes Promoted by Sodium tri(<i>sec</i>-butyl)borohydride

Alkoxysilanes find application in many areas of chemistry ranging from research-scale organic synthesis to multi-ton production of materials. Classically, they are obtained in stoichiometric reaction of alcoholysis of chlorosilanes, however, recent years brought development in the field of direct dehydrogenative coupling of hydrosilanes with alcohols, which is a more atom-economic and benign alternative to the former process. In this paper, we report the use of sodium tri(sec-butyl)borohydride as a convenient promoter of this reaction. Exemplary syntheses carried out under mild conditions and without additional solvents, followed by very easy work-up procedure, show excellent potential for application of so devised catalytic system

Hydroboration of Terminal Alkynes Catalysed by Sodium Triethylborohydride

Sodium triethylborohydride - commonly used as a reducing agent for hydroboration catalysts based on the first-row transition metal complexes with tridentate ligands, has been found a highly selective catalyst for hydroboration of terminal alkynes. Hydroboration of aromatic and aliphatic alkynes with pinacolborane in the presence of 10 mol% of NaHBEt3 proceeded in a highly selective manner to give (E)-vinylboronate esters with high yields, whereas ethynylsilanes seem to be less reactive in this process

Hydrogermylation initiated by trialkylborohydrides: a living anionic mechanism

Sodium trialkylborohydrides were found to be selective catalysts for the hydrogermylation of aromatic alkenes. Addition of phenylgermane and diphenylgermane in the presence of 10 mol% of NaHB(sec-Bu)3 proceeded in a highly selective manner to give – in contrast to the analogous hydrosilylation process – β-germylated products. The nature of this process was explained with the aid of DFT calculations and it was proposed that the mechanism proceeds via a trisubstituted germanide anion whose attack on the terminal vinyl carbon is the source of selectivity

In situ Mo(CO)₆-based catalysts for alkyne metathesis: Silanols vs phenols as co-catalysts under thermal and photochemical activation

International audienceA systematic study on the use of silanols and phenols as effective activators in Mo(CO)₆-based catalytic systems for metathesis of 4-decyne and 1-phenyl-1-propyne is reported. In comparison with traditionally used phenols, aryl-substituted silanols exhibit high activating potential of molybdenum species even at lower concentrations (2 mol% of Mo(CO)₆ and 4-20 mol% of silanol depending on the alkyne) at toluene reflux. Silylated phenols and silanols are also suitable as co-catalysts. Additionally, Mo(CO)₆/silanol catalytic system is shown to be efficiently activated by UV-irradiation at room temperature, whereas it is less effective for metathesis reactions performed in the presence of phenols