Wyniki wyszukiwania - BazTech

Ograniczanie wyników

Powiadomienia systemowe

Sesja wygasła!
Sesja wygasła!

Znaleziono wyników: 2

Liczba wyników na stronie

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych: coupling reactions

Sortuj według:

Ogranicz wyniki do:

Karbeny N-heterocykliczne : synteza i zastosowanie

Malinowska M., Hryniewicka A.

Wiadomości Chemiczne

2015

[Z] 69, 3-4

227--253

N-Heterocyclic carbenes (NHCs) are powerful tools in organic chemistry, with numerous applications in academic and industrial laboratories. They are usually defined as singlet carbenes, in which the divalent carbonic centre is connected directly to at least one nitrogen atom in the heterocycle [1]. They have played an important role in organic chemistry ever since the first evidence of their existence. The isolation of stable, free 1,3‑diadamantylimidazol-2-ylidene (IAd, Fig. 1) by Arduengo et al. in 1991 was a milestone in the chemistry of carbenes [2]. From the beginnings as academic curiosities, N‑heterocyclic carbenes today are very useful compounds in a variety of organic transformations (Fig. 13). NHCs are neutral σ-donors, which form very strong bonds with the majority of transition metals (stronger than phosphines). These compounds are easy-to-make ligands with great potential in homogeneous catalysis (mainly ruthenium and palladium complexes) for large number of reactions, including the coupling reactions (Heck, Negishi, Stille, Suzuki or Sonogashira reactions) and olefin metathesis [3]. Moreover, they are very useful as organocatalysts used in the benzoin condensation, the Stetter reaction and ring-opening polymerization (ROP) or transesterification [4]. In this review, we aim to give an overview of the properties and applications of NHCs, which we expect will be a useful introduction for chemists interested in studying and applying these important compounds. The first part of this review is devoted to the main synthetic routes to NHCs, their properties and reactivity. In the second part we describe the metal complexes with NHCs as homogeneous catalysts and their applications in various types of reactions. At the end of this part of the paper the use of NHCs as organocatalysts is presented.

Nickel Mediated Coupling of Organic Ligands

Pasynkiewcz S., Pietrzykowski A., Olędzka E., Wang J.

Polish Journal of Chemistry

2003

Vol. 77 / nr 5

701-707

Reactions of nickelocene, NiCp2, with organolithium compounds RLi (R = -C_CPh; -CPh=CPh2; -CPh3, -CPh2SiMe3), where R does not contain _- and _-hydrogen atoms, have been studied. It was found that {CpNiR}, formed in the first step of the reaction, underwent coupling with the formation of {(NiCp)2} and R-R. As organolithium substrates are readily available, and yield of coupling products was high (from over 60% to ~ 90%), the studied reactions could be applied as synthetic methods for preparation of wide range of R-R type organic compounds. In order to improve yield of the products and to prevent very active {(NiCp)2} species from further reactions, NiCp2 and LiR were reacted in the presence of PhC_CMe, what led to the formation of only two products: (NiCp)2_PhC_CMe complex and R-R. These products were easily separated by column chromatography on neutral alumina, leading to the isolation of R-R in high yield.