The replacement of noble metal technologies and the realization of new reactivities with earth‐abundant metals is at the heart of sustainable synthesis. Alkene hydrogenations have so far been most effectively performed by noble metal catalysts. This study reports an iron‐catalyzed hydrogenation protocol for tri‐ and tetra‐substituted alkenes of unprecedented activity and scope under mild conditions (1–4 bar H2, 20 °C). Instructive snapshots at the interface of homogeneous and heterogeneous iron catalysis were recorded by the isolation of novel Fe nanocluster architectures that act as catalyst reservoirs and soluble seeds of particle growth.
Iron(0) nanoparticles in ionic liquids (ILs) have been shown to catalyse the semi-hydrogenation of alkynes. In the presence of a nitrile-functionalised IL or acetonitrile, stereoselective formation of (Z)-alkenes was observed. The biphasic solvent system allowed facile separation and re-use of the catalyst.
Catalyzing C À Cbond-forming reactions with earthabundant metals under mild conditions is at the heart of sustainable synthesis.T he cyclotrimerization of alkynes is av aluable atom-efficient reaction in organic synthesis that is enabled by several metal catalysts,i ncluding iron. This study reports an effective iron-catalyzedc yclotrimerization for the regioselective synthesis of 1,2,4-substituted arenes (1 mol % catalyst, toluene,2 08 8C, 5min). Ad ual activation mechanism (substrate deprotonation, reductive elimination) renders the simple Fe II precatalyst highly active in the absence of any reductant.Metal-catalyzed cyclotrimerization reactions of alkynes constitute akey approach for the construction of substituted aromatic compounds and have been developed to great maturity since their first discovery in the mid-19th century and the early studies of Reppe in 1948.[1] Today,s everal transition metals display good catalytic activity in this highly atom-efficient, redox-neutral, complexity-generating reaction.[2] Thes earch for sustainable base-metal approaches has recently prompted the development of iron-catalyzed processes.[3] High activities were especially observed with lowvalent iron catalysts,w hich can be generated from iron(0) precursors or by reactions of Fe II complexes with suitable reductants.T he first report utilized iron carbonyl catalysts at high temperatures.[4] Recently,v arious combinations of iron complexes,ligands,and zinc have been shown to exhibit high catalytic activity and wide applicability.[5] Alternatively,elaborate iron complexes in low oxidation states (+ 1, 0) have also been applied.[6] Most catalyst developments were fueled by the notion that al ow-valent iron species would engage in coordinative activation of the softly Lewis basic alkyne, facilitate the iron-centered oxidative cyclization step,a nd be regenerated upon reductive elimination. However,t hese methods require the preparation and handling of highly reactive iron complexes or the presence of suitable reductants.T he conceptual relation between reductants and bases led us to postulate amechanistically distinct approach to the design of effective iron(II) precatalysts in which as imple internal base would mimic the role of an external reductant. With one equivalent of at erminal alkyne,adual activation mechanism of the inactive FeX 2 involving sequential alkyne deprotonation and reductive alkyne elimination would result in an overall reduction in the absence of an actual reductant (Scheme 1). We surmised that FeX 2 complexes constitute most simple precatalysts with inexpensive,e asily accessible ligands Xt hat are bulky (facile dissociation), strongly basic (alkyne deprotonation), and lipophilic (solubility in organic solvents).With these framework conditions,weinvestigated various ferrous salts and identified iron(II) bis(1,1,1,3,3,3-hexamethyldisilazan-2-ide) (Fe(hmds) 2 )a sa na ctive catalyst. Documented herein are the benefits of this simple catalytic system, which presents tangible advances over the cu...
The scope and mechanism of a practical protocol for the iron-catalyzed hydrogenation of alkenes and alkynes at 1 bar H2 pressure were studied.
The replacement of noble metal technologies and the realization of new reactivities with earth-abundant metals is at the heart of sustainable synthesis.Alkene hydrogenations have so far been most effectively performed by noble metal catalysts. This study reports an iron-catalyzedh ydrogenation protocol for tri-and tetra-substituted alkenes of unprecedented activity and scope under mild conditions (1-4 bar H 2 ,2 08 8C). Instructive snapshots at the interface of homogeneous and heterogeneous iron catalysis were recorded by the isolation of novel Fe nanocluster architectures that act as catalyst reservoirs and soluble seeds of particle growth.
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