Denticity

About: Denticity is a research topic. Over the lifetime, 17851 publications have been published within this topic receiving 309492 citations.

Asymmetric hydrogenation using monodentate phosphoramidite ligands.

Abstract: Monodentate phosphoramidites are excellent ligands for Rh-catalyzed asymmetric hydrogenations of substituted olefins Enantioselectivities between 95 and 99% were obtained in the asymmetric hydrogenation of protected α- and β-dehydroamino acids and esters, itaconic acid and esters, aromatic enamides, aromatic enol esters, aromatic and aliphatic enol carbamates, and α-substituted cinnamic acids An iridium catalyst Ir(L*)(COD)Cl was developed that contains only a single bulky phosphoramidite based on 3,3′-disubstituted BINOL or bisphenol as a chiral ligand With this catalyst, acetylated dehydroamino acid esters could be hydrogenated with very good enantioselectivity Most reactions have turnover frequencies of 250–1600 h −1, depending upon the hydrogen pressure The enantioselectivity is unaffected by the pressure over a wide range Because of their modularity and easy synthesis, parallel ligand synthesis is possible Results obtained with these library ligands deviate only slightly from those obtained wi

A readily available chiral Ag-based N-heterocyclic carbene complex for use in efficient and highly enantioselective Ru-catalyzed olefin metathesis and Cu-catalyzed allylic alkylation reactions.

Abstract: A new chiral bidentate N-heterocyclic carbene (NHC) ligand has been designed and synthesized. The NHC ligand bears a chiral diamine backbone and an achiral biphenol group; upon metal complexation (derived from Ag(I), Ru(II), or Cu(II)), the diamine moiety induces >98% diastereoselectivity such that the biaryl unit coordinates to the metal center to afford the desired complex as a single atropisomer. Because the ligand does not require optically pure biaryl amino alcohols, its synthesis is significantly shorter and simpler than the related first generation ligands bearing a chiral binaphthyl-based amino alcohol. The chiral NHC ligand can be used in the preparation of highly effective Ru- and Cu-based complexes (prepared and used in situ from the Ag(I) carbene) that promote enantioselective olefin metathesis and allylic alkylations with scope that is improved from previously reported protocols. In many cases, transformations promoted by the chiral NHC-based complexes proceed with higher enantioselectivity and reactivity than was observed with previously reported complexes.

The Development of Bidentate P,N Ligands for Asymmetric Catalysis

Abstract: In this review, an attempt is made to systemise the role which bidentate phosphinamine (P,N) ligands play in asymmetric catalysis. The ligands will be classified, not by the reaction to which their metal complexes have been applied, but by the nature of their donor atoms. In this manner the development of ligand architectural design can be more easily monitored. The asymmetric transformations to which metal complexes of these ligands have been applied include among others, palladium-catalysed allylic substitutions, copper-catalysed 1,4-additions to enones and rhodium-catalysed hydroboration of vinylarenes. Excellent enantioselectivities, regioselectivities and reactivities have been achieved in each of these processes.