Cooperative Activation Effect Research Articles

Unusual pathway of epoxide hydration over a novel CoIII(salen)-based pseudohomogeneous catalyst with excellent performance

Due to high H2O/epoxide molar ratio for non-catalytic hydration, industrial production of bulk chemicals 1,2-diols is much energy-intensive. As a very promising route to produce 1,2-diols with low energy consumption, catalytic hydration of epoxides has aroused much interest from both academy and industry. The key is to develop a catalyst with high activity and stability at a low H2O/epoxide molar ratio. It has been demonstrated that encapsulating a homogeneous catalytic species into the cavity of porous material is a very efficient way to obtain a high-performance heterogeneous catalyst. Herein, a novel pseudohomogeneous catalyst with the distinctive Co(salen)-PF6 encapsulated in nanocages of a typical mesoporous material FDU-12 has been successfully developed, which exhibits both unexpectedly tremendously enhanced activity at the low H2O/epoxide molar ratio close to stoichiometric ratio and unique surprising recyclability without regeneration between runs in propylene oxide hydration. Especially, based on the systematic experimental design/implementation, particular structural characterizations and in-depth calculations, the pathway the newly developed catalyst going through has been investigated and determined to be an unusual bisubstrate-directly-activated cooperative mechanism (i.e. a bimolecular cooperative activation mechanism not involving Co(salen)–OH). The cooperative activation effect gives rise to the unexpectedly tremendously enhanced activity of our new catalyst, while no involving of Co(salen)–OH during the catalytic process leads to its best and unique catalytic stability in epoxide hydration among all the reported CoIII(salen)-based heterogeneous catalyst. It is believed that this study and the developed catalyst are of great significance for developing the catalytic hydration technology with low energy consumption and for developing high-performance heterogeneous catalysts.

Facile C-N coupling of coordinated ammonia and labile carbonyl or acetonitrile promoted by a thiolate-bridged dicobalt reaction scaffold.

At low temperature, interaction of the thiolate-bridged dicobalt carbonyl complex [Cp*Co(i)(μ-SEt)2(CO)CoCp*][I] (Cp* = η5-C5Me5) (1) with NH3 resulted in the C-N coupling of the coordinated CO and amido group that originate from ammonia activation to afford a dicobalt formylamino complex [Cp*Co(μ-SEt)2(μ-η1:η1-O[double bond, length as m-dash]CNH2)CoCp*][I] (2). Interestingly, at relatively high temperatures, the labile CO ligand was replaced by NH3 to give a thiolate-bridged dicobalt ammonia complex [Cp*Co(i)(μ-SEt)2(NH3)CoCp*][I] (3). Subsequently, in the presence of the dehalogenation reagent AgPF6, the Co2S2 scaffold can simultaneously activate NH3 and MeCN to produce the complex [Cp*Co(MeCN)(μ-SEt)2(NH3)CoCp*][PF6]2 (4). Furthermore, in the presence of NaOEt, the facile occurrence of the intramolecular cyclization led to the formation of acetamidino-bridged dicobalt complex [Cp*Co(μ-SEt)2(μ-η1:η1-NH(CCH3)NH)CoCp*][PF6] (5), which may proceed through the nucleophilic attack of amido from NH3 to coordinated MeCN followed by the hydrogen atom transfer process. In the presence of MeCN, treatment of 5 with HBF4 released the corresponding [MeC(NH2)NH2]BF4; meanwhile, the [Co2S2] core structural scaffold remained. In this Co2S2 reaction system, the cooperative activation effect between the two cobalt centers plays an important role for NH3 activation and functionalization.

Cooperative activation effect on H2O adsorption in MnO–Co catalyzed steam methane reforming

Steam methane reforming is a very important chemical process in hydrogen production and solid oxide fuel cells (SOFCs). Cobalt (Co) is an important catalyst for dry and steam methane reforming. However, previous studies have confirmed that metal Co surfaces only have weak adsorption activity for H2O, which is evidently unfavorable for steam reforming. In this work we used first-principles simulations to study the activity of MnO–Co catalysts for the adsorption of H2O. Compared with the Co (111) surface and pristine Co clusters, the MnO–Co catalytic layer has a stronger adsorption capability for H2O because of the introduction of the MnO substrate, which is crucial for improving the steam reforming reaction and inhibiting carbon disposition in SOFCs. The cooperation mechanism between MnO and Co is discussed based on the analysis of electronic structures. The conclusions from this work are universal for other metal-oxide composite catalyst layers.

Cationic Zn-Porphyrin Polymer Coated onto CNTs as a Cooperative Catalyst for the Synthesis of Cyclic Carbonates.

The development of solid catalysts containing multiple active sites that work cooperatively is very attractive for biomimetic catalysis. Herein, we report the synthesis of bifunctional catalysts by supporting cationic porphyrin-based polymers on carbon nanotubes (CNTs) using the direct reaction of 5,10,15,20-tetrakis(4-pyridyl)porphyrin zinc(II), di(1H-imidazol-1-yl)methane, and 1,4-bis(bromomethyl)benzene in the presence of CNTs. The bifunctional catalysts could efficiently catalyze the cycloaddition reaction of epoxides and CO2 under solvent-free conditions with porphyrin zinc(II) as the Lewis acid site and a bromine anion as a nucleophilic agent working in a cooperative way. Furthermore, a relative amount of porphyrin zinc(II) and quaternary ammonium bromide could be facilely adjusted for facilitating cooperative behavior. The bifunctional catalyst with a TOF up to 2602 h-1 is much more active than the corresponding homogeneous counterpart and is one of the most active heterogeneous catalysts ever reported under cocatalyst-free conditions. The high activity is mainly attributed to the enhanced cooperation effect of the bifunctional catalyst. With a wide substrate scope, the bifunctional catalyst could be stably recycled. This work demonstrates a new approach for the generation of a cooperative activation effect for solid catalysts.

Cocatalyst‐Free Hybrid Ionic Liquid (IL)‐Based Porous Materials for Efficient Synthesis of Cyclic Carbonates through a Cooperative Activation Pathway

Cocatalyst-free ionic liquid (IL)-based porous polymers (Px -Vy -OHz R) functionalized with an intermolecular hydroxyl group were prepared by means of radical copolymerization of 1-butyl-3-vinylimidazolium bromide, (4-vinylphenyl)methanol (VBzOH), and divinylbenzene (DVB) under solvothermal conditions. As the ratio of 4-vinylphenylmethanol in the initial mixture increased, the content of the hydroxyl groups in the polymer increased from 3.35 to 5.35 mmol g-1 and the Brunauer-Emmett-Teller (BET) surface area of the polymer decreased sharply from 365 to 2.5 m2 g-1 . In the carbonation of CO2 and epoxides, the turnover frequency (TOF) of Px -Vy -OHz R increased gradually from 25 to 67 h-1 as the OH ratio increased irrespective of the sharp decrease in BET surface area, which suggests the existence of a cooperative activation effect between OH and ILs. To obtain a high OH content while still maintaining a high BET surface area, hybrid porous materials (SBA-[Vx OHy ]R-n) were prepared by means of copolymerization of 1-ethyl-3-vinylimidazolium bromide and 4-vinylphenylmethanol in the mesopores of SBA-15. SBA-[Vx OHy ]R-n was more active than its polymer counterpart (TOF: 188 versus 71 h-1 ) in the cycloaddition of CO2 with propyl oxide owing to the combined effect of the high BET surface area and the high OH content. The hybridization of mesoporous materials with polymers represents an efficient strategy for the preparation of high-performance solid catalysts for chemical transformations.

Hydration of Epoxides on [CoIII(salen)] Encapsulated in Silica‐Based Nanoreactors

A confined workspace has its benefits in the case of a non-acid solid catalyst prepared by encapsulating [CoIII(salen)] in the nanocages of mesoporous silica. The catalytic activity and selectivity of [CoIII(salen)] were increased significantly owing to the enhanced cooperative activation effect in the nanoreactors. Thus, ethylene oxide (EO) underwent hydration at a low 2:1 H2O/EO molar ratio to give ethylene glycol in up to 96 % yield.

Asymmetric Catalysis with Metal Complexes in Nanoreactors

Recently, the field of heterogeneous asymmetric catalysis, generally using chiral solid catalysts, has attracted much attention in the production of single enantiomers. Among versatile chiral solid catalysts, chiral metal complexes confined in nanoreactors often exhibit very unique enantioselectivity and catalytic activity compared to homogeneous catalysts. In this Focus Review, we summarize the recent advances in asymmetric reactions on chiral metal complexes confined in nanoreactors with an emphasis on the confinement effect and cooperative activation effect of the nanoreactor and new strategies for the preparation of chiral solid catalysts, such as the encapsulation of chiral metal complexes in the nanocages of mesoporous silica and incorporation of chiral ligands in the network of mesoporous organosilicas.

Enhanced Cooperative Activation Effect in the Hydrolytic Kinetic Resolution of Epoxides on [Co(salen)] Catalysts Confined in Nanocages

The solid catalyst with high catalytic activity and enantioselectivity in the hydrolytic kinetic resolution (HKR) of epoxides was prepared by confining Co(Salen) in the nanocage of SBA-16 through reducing the pore entrance size using a silylation method. It was found that the activity of the solid catalysts increased with the number of [Co(Salen)] molecules per nanocage increasing, and the solid catalyst with more than two chiral [Co(Salen)] molecules in one nanocage of SBA-16 exhibits much higher activity and enantioselectivity than the homogeneous [Co(Salen)] catalyst in the HKR of epoxides at low substrate/catalyst ratio. The significantly improved activity of the solid catalyst is due to a high local concentration of [Co(Salen)] in nanospace because of the enhanced cooperative activation effect of [Co(Salen)] molecules.

Enhanced Cooperative Activation Effect in the Hydrolytic Kinetic Resolution of Epoxides on [Co(salen)] Catalysts Confined in Nanocages

Enhanced Cooperative Activation Effect in the Hydrolytic Kinetic Resolution of Epoxides on [Co(salen)] Catalysts Confined in Nanocages

Supramolecular interactions of solid human serum albumin with binary mixtures of solvent vapors

Sorption isotherms of organic compounds on solid human serum albumin (HSA) from binary vapor mixtures were determined by gas chromatographic headspace analysis. The shape of sorption isotherms depends on molecular structure of studied sorbates. The ‘active’ compounds capable to sorb effectively on dry HSA increase the sorption of ‘passive’ compounds unable to be sorbed by dry HSA in absence of the third component. The critical hydration of HSA is required for sorption activation of ‘passive’ sorbates if water is taken as ‘active’ component. Ethanol and acetonitrile exhibit such activation effect without threshold. ‘Passive’ sorbates are able to produce cooperative activation effect on the sorption of ‘active’ component. Hydration history effect is observed for sorption on prehydrated HSA and HSA hydrated in situ. Obtained results were interpreted in terms of clathrate formation by ‘passive’ sorbate (substrate) and ‘active’ component inside the HSA (receptor) binding centers.