Asymmetric Catalytic Hydroamination of Activated Olefins in Ionic Liquids

Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

Ionic liquids (ILs) have unique physicochemical properties that make them advantageous for catalysis, such as low vapor pressure, non-flammability, high thermal and chemical stabilities, and the ability to enhance the activity and stability of (bio)catalysts. ILs can improve the efficiency, selectivity, and sustainability of bio(transformations) by acting as activators of enzymes, selectively dissolving substrates and products, and reducing toxicity. They can also be recycled and reused multiple times without losing their effectiveness. ILs based on imidazolium cation are preferred for structural organization aspects, with a semiorganized layer surrounding the catalyst. ILs act as a container, providing a confined space that allows modulation of electronic and geometric effects, miscibility of reactants and products, and residence time of species. ILs can stabilize ionic and radical species and control the catalytic activity of dynamic processes. Supported IL phase (SILP) derivatives and polymeric ILs (PILs) are good options for molecular engineering of greener catalytic processes. The major factors governing metal, photo-, electro-, and biocatalysts in ILs are discussed in detail based on the vast literature available over the past two and a half decades. Catalytic reactions, ranging from hydrogenation and cross-coupling to oxidations, promoted by homogeneous and heterogeneous catalysts in both single and multiphase conditions, are extensively reviewed and discussed considering the knowledge accumulated until now.

Synthesis and characterization of enantiopure planar-chiral phosphorus-linked diferrocenes

Six new homochiral diferrocenyl derivatives have been synthesized, one of which is purely planar–chiral. Even if the two diferrocene subunits are identical, they are distinguished due to their positions relative to the substituents at the phospho­rous prochiral centre.

In the course of an ongoing synthetic project on cyclic diferrocenylphosphines, we obtained a group of planar–chiral diferrocenyl com­pounds useful as precursors for subsequent cyclization. Here we report the crystal structures of two sym­metric com­pounds [(Fc^A)₂(Ph)P], one of which contains four stereogenic centres (two C chiral and two planar chiral centres), i.e. 1,1′-(phenyl­phos­phane­di­yl)bis­{(2S_p)-2-[(1R)-1-(acet­yloxy)eth­yl]ferrocene}, [Fe₂(C₅H₅)₂(C₂₄H₂₅O₄P)], and the other phosphine sulfide is a purely planar–chiral com­pound (two planar chiral centres), i.e. bis[(2S_p)--2-ethenylferrocen-1-yl]phenylphosphane sulfide, [Fe₂(C₅H₅)₂(C₂₀H₁₇PS)]. Owing to the stereocentres present, reactions performed on [(Fc^A)₂(Ph)P]-type com­pounds strongly favour one ferrocene unit over the other due to diastereoselectivity. Furthermore, we present four related structures where the ferrocene units are not identical [(Fc^A)(Fc^B)(Ph)P]. These are {(2S_p)-2-[(1R)-1-(acet­yloxy)eth­yl]ferrocen-1-yl}[(2S_p)-2-ethenylferrocen-1-yl]phenyl-(S)-phosphine sulfide, [Fe₂(C₅H₅)₂(C₂₂H₂₁O₂PS)], [(2S_p)-2-ethenylferrocen-1-yl]{(2S_p)-2-[(1R)-1-hy­droxy­eth­yl]ferrocen-1-yl}phenyl-(S)-phosphine sulfide, [Fe₂(C₅H₅)₂(C₂₀H₁₉OPS)], {(2S_p)-2-[(1R)-1-(acet­yloxy)eth­yl]ferro­cen-1-yl}{(2S_p)-2-[(1R)-1-hy­droxy­eth­yl]ferrocen-1-yl}phenyl-(R)-phos­phine sulfide, [Fe₂(C₅H₅)₂(C₂₂H₂₃O₃PS)], and {(2S_p)-2-[(1R)-1-benzyl­amino)­eth­yl]ferrocen-1-yl}[(2S_p)-2-ethenylferrocen-1-yl]phenyl-(S)-phosphine sulfide, [Fe₂(C₅H₅)₂(C₂₇H₂₆NPS)]. All of the structures are accessible in one step from known precursors.

Planar-Chiral P and N-bridged Diferrocenes

We describe the synthesis of planar-chiral diferrocene compounds 4, 7 and 12, intended as key precursors for a new family of asymmetric catalyst ligands with less complex structures than their popular equivalents. In contrast to conventional 1,2-disubstituted ferrocenes containing center-chiral and planar-chiral elements, these compounds are purely planar-chiral due to the absence of α-substiuted ethyl groups. The title compounds 4, 7 and 12 were obtained from known precursors in 87%, 59% and 60% yields, respectively.

Recent Advances in Metal-Catalyzed Asymmetric 1,4-Conjugate Addition (ACA) of Nonorganometallic Nucleophiles

The metal-catalyzed asymmetric conjugate addition (ACA) reaction has emerged as a general and powerful approach for the construction of optically active compounds and is among the most significant and useful reactions in synthetic organic chemistry. In recent years, great progress has been made in this area with the use of various chiral metal complexes based on different chiral ligands. This review provides comprehensive and critical information on the enantioselective 1,4-conjugate addition of nonorganometallic (soft) nucleophiles and their importance in synthetic applications. The literature is covered from the last 10 years, and a number of examples from before 2007 are included as background information. The review is divided into multiple parts according to the type of nucleophile involved in the reaction (such as C-, B-, O-, N-, S-, P-, and Si-centered nucleophiles) and metal catalyst systems used.

Synthesis and catalytic application of [PPP]-pincer iron, nickel and cobalt complexes for the hydrosilylation of aldehydes and ketones

The catalytic performance of [PPP]-pincer hydrido Fe, Ni and Co complexes for the hydrosilylation of aldehydes and ketones was explored.

Conjugate addition-enantioselective protonation reactions

The addition of nucleophiles to electron-deficient alkenes represents one of the more general and commonly used strategies for the convergent assembly of more complex structures from simple precursors. In this review the addition of diverse protic and organometallic nucleophiles to electron-deficient alkenes followed by enantioselective protonation is summarized. Reactions are first categorized by the type of electron-deficient alkene and then are further classified according to whether catalysis is achieved with chiral Lewis acids, organocatalysts, or transition metals.

Bond and small-molecule activation with low-valent nickel complexes

The use of nickel compounds in low oxidation states allowed a variety of useful transformations of interest for academia, industry and in the solution of environmental issues.

Imidazolium-Tagged Ferrocene Ligands

New chiral imidazolium-tagged ferrocene ligands were prepared. Diastereoselective ortho-lithiation of the Ugi amine was employed in the synthesis of planar chiral P/P, P/N and Se/N ligands. These compounds were attached through six-carbon spacers to an imidazolium moiety. Pd-complexes of these ligands were successfully used as catalysts for asymmetric allylic substitution in ionic liquids.