A Dicationic Ruthenium Alkylidene Complex for Continuous Biphasic Metathesis Using Monolith‐Supported Ionic Liquids

A dicationic ruthenium–alkylidene complex [Ru(dmf)₃(IMesH₂)(?CH‐2‐(2‐PrO)‐C₆H₄)][(BF₄)₂] ( 1 ; IMesH₂=1,3‐dimesitylimidazolin‐2‐ylidene) has been prepared and used in continuous metathesis reactions by exploiting supported ionic‐liquid phase (SILP) technology. For these purposes, ring‐opening metathesis polymerization (ROMP)‐derived monoliths were prepared from norborn‐2‐ene, tris(norborn‐5‐ene‐2‐ylmethyloxy)methylsilane, and [RuCl₂(PCy₃)₂(CHPh)] (Cy=cyclohexyl) in the presence of 2‐propanol and toluene and surface grafted with norborn‐5‐en‐2‐ylmethyl‐N,N,N‐trimethylammonium tetrafluoroborate ([NBE‐CH₂‐NMe₃][BF₄]). Subsequent immobilization of the ionic liquid (IL), 1‐butyl‐2,3‐dimethylimidazolium tetrafluoroborate ([BDMIM][BF₄]), containing ionic catalyst 1 created the SILP catalyst. The use of a second liquid transport phase, which contained the substrate and was immiscible with the IL, allowed continuous metathesis reactions to be realized. High turnover numbers (TONs) of up to 3700 obtained in organic solvents for the ring‐closing metathesis (RCM) of, for example, N,N‐diallyltrifluoroacetamide, diethyl diallylmalonate, diethyl di(methallyl)malonate, tert‐butyl‐N,N‐diallylcarbamate, N,N‐diallylacetamide, diphenyldiallylsilane, and 1,7‐octadiene, as well as in the self‐metathesis of methyl oleate, could be further increased by using biphasic conditions with [BDMIM][BF₄]/heptane. Under continuous SILP conditions, TONs up to 900 were observed. Due to the ionic character of the initiator, catalyst leaching into the transport phase was very low (<0.1 %). Finally, the IL can, together with decomposed catalyst, be removed from the monolithic support by flushing with methanol. Upon reloading with [BDMIM][BF₄]/ 1 , the recycled support material again qualified for utilization in continuous metathesis reactions.     

Ionic Liquids as Precursors for Efficient Mesoporous Iron‐Nitrogen‐Doped Oxygen Reduction Electrocatalysts

A ferrocene‐based ionic liquid (Fe‐IL) is used as a metal‐containing feedstock with a nitrogen‐enriched ionic liquid (N‐IL) as a compatible nitrogen content modulator to prepare a novel type of non‐precious‐metal–nitrogen–carbon (M‐N‐C) catalysts, which feature ordered mesoporous structure consisting of uniform iron oxide nanoparticles embedded into N‐enriched carbons. The catalyst Fe¹⁰@NOMC exhibits comparable catalytic activity but superior long‐term stability to 20 wt % Pt/C for ORR with four‐electron transfer pathway under alkaline conditions. Such outstanding catalytic performance is ascribed to the populated Fe (Fe₃O₄) and N (N2) active sites with synergetic chemical coupling as well as the ordered mesoporous structure and high surface area endowed by both the versatile precursors and the synthetic strategy, which also open new avenues for the development of M‐N‐C catalytic materials.     

Facile Access to Transition‐Metal–Carbonyl Complexes with an Amidinate‐Stabilized Chlorosilylene Ligand

Three transition‐metal–carbonyl complexes [V( L )(CO)₃(Cp)] ( 1 ), [Co( L )(CO)(Cp)] ( 2 ), and [Co( L₂ )(CO)₃]⁺[CoCO)₄]^? ( 3 ), each containing stable N‐heterocyclic‐chlorosilylene ligands ( L ; L =PhC(NtBu)₂SiCl) were synthesized from [V(CO)₄(Cp)], [Co(CO)₂(Cp)], and Co₂(CO)₈, respectively. Complexes 1 , 2 , 3 were characterized by NMR and IR spectroscopy, EI‐MS spectrometry, and elemental analysis. The molecular structures of compounds 1 , 2 , 3 were determined by single‐crystal X‐ray diffraction.     

Transition‐Metal‐Ion‐Mediated Polymerization of Dopamine: Mussel‐Inspired Approach for the Facile Synthesis of Robust Transition‐Metal Nanoparticle–Graphene Hybrids

Inspired by the high transition‐metal‐ion content in mussel glues, and the cross‐linking and mechanical reinforcement effects of some transition‐metal ions in mussel threads, high concentrations of nickel(II), cobalt(II), and manganese(II) ions have been purposely introduced into the reaction system for dopamine polymerization. Kinetics studies were conducted for the Ni²⁺–dopamine system to investigate the polymerization mechanism. The results show that the Ni²⁺ ions could accelerate the assembly of dopamine oligomers in the polymerization process. Spectroscopic and electron microscopic studies reveal that the Ni²⁺ ions are chelated with polydopamine (PDA) units, forming homogeneous Ni²⁺–PDA complexes. This facile one‐pot approach is utilized to construct transition‐metal‐ion–PDA complex thin coatings on graphene oxide, which can be carbonized to produce robust hybrid nanosheets with well‐dispersed metallic nickel/metallic cobalt/manganese(II) oxide nanoparticles embedded in PDA‐derived thin graphitic carbon layers. The nickel–graphene hybrid prepared by using this approach shows good catalytic properties and recyclability for the reduction of p ‐ nitrophenol.     

The Co‐Entrapment of a Homogeneous Catalyst and an Ionic Liquid by a Sol–gel Method: Recyclable Ionogel Hydrogenation Catalysts

Molecular hydrogenation catalysts have been co‐entrapped with the ionic liquid [Bmim]NTf₂ inside a silica matrix by a sol–gel method. These catalytic ionogels have been compared to simple catalyst‐doped glasses, the parent homogeneous catalysts, commercial heterogeneous catalysts, and Rh‐doped mesoporous silica. The most active ionogel has been characterised by transmission electron microscopy, X‐ray photoelectron spectroscopy, and solid state NMR before and after catalysis. The ionogel catalysts were found to be remarkably active, recyclable and resistant to chemical change.     

Diastereo‐ and Enantioselective anti‐Selective Hydrogenation of α‐Amino‐β‐keto Ester Hydrochlorides and Related Compounds Using Transition‐Metal–Chiral‐Bisphosphine Catalysts

This review describes our recent works on the diastereo‐ and enantioselective synthesis of anti‐β‐hydroxy‐α‐amino acid esters using transition‐metal–chiral‐bisphosphine catalysts. A variety of transition metals, namely ruthenium (Ru), rhodium (Rh),iridium (Ir), and nickel (Ni), in combination with chiral bisphosphines, worked well as catalysts for the direct anti‐selective asymmetric hydrogenation of α‐amino‐β‐keto ester hydrochlorides, yielding anti‐β‐hydroxy‐α‐amino acid esters via dynamic kinetic resolution (DKR) in excellent yields and diastereo‐ and enantioselectivities. The Ru‐catalyzed asymmetric hydrogenation of α‐amino‐β‐ketoesters via DKR is the first example of generating anti‐β‐hydroxy‐α‐amino acids. Complexes of iridium and axially chiral bisphosphines catalyze an efficient asymmetric hydrogenation of α‐amino‐β‐keto ester hydrochlorides via dynamic kinetic resolution. A homogeneous Ni–chiral‐bisphosphine complex also catalyzes an efficient asymmetric hydrogenation of α‐amino‐β‐keto ester hydrochlorides in an anti‐selective manner. As a related process, the asymmetric hydrogenation of the configurationally stable substituted α‐aminoketones using a Ni catalyst via DKR is also described.     

Mild and Selective Catalytic Hydrogenation of the C=C Bond in α,β‐Unsaturated Carbonyl Compounds Using Supported Palladium Nanoparticles

Chemoselective reduction of the C=C bond in a variety of α,β‐unsaturated carbonyl compounds using supported palladium nanoparticles is reported. Three different heterogeneous catalysts were compared using 1 atm of H₂: 1) nano‐Pd on a metal–organic framework (MOF: Pd⁰‐MIL‐101‐NH₂(Cr)), 2) nano‐Pd on a siliceous mesocellular foam (MCF: Pd⁰‐AmP‐MCF), and 3) commercially available palladium on carbon (Pd/C). Initial studies showed that the Pd@MOF and Pd@MCF nanocatalysts were superior in activity and selectivity compared to commercial Pd/C. Both Pd⁰‐MIL‐101‐NH₂(Cr) and Pd⁰‐AmP‐MCF were capable of delivering the desired products in very short reaction times (10–90 min) with low loadings of Pd (0.5–1 mol %). Additionally, the two catalytic systems exhibited high recyclability and very low levels of metal leaching.