Recent advances in Ni-Al bimetallic catalysis for unreactive bond transformation

Ni-Al bimetallic catalysis proves to be an efficient catalytic strategy for unreactive bond transformations. Recently, chiral bifunctional ligands, especially amphoteric secondary phosphine oxide(SPO) ligand, are used for a more powerful synergistic effect in the bimetal-catalyzed reactions, providing not only milder reaction conditions and higher reactivity but also excellent reaction selectivity. Herein, we give a brief review on the development of Ni-Al bimetallic catalytic system and highlight recent advances in enantioselective Ni-Al bimetallic catalysis for unreactive bond transformation.

Bimetallic water oxidation: One-site catalysis with two-sites oxidation

Water oxidation is the key half reaction to achieve full splitting of water to hydrogen and oxygen.Herein,a binuclear complex,[(L^(4-))Co_(2)~Ⅲ(OH)]ClO_(4),was reported as a stable and efficient homogenous catalyst for electrocatalytic water oxidation in 0.1 M phosphate buffer(pH 7.0).Cyclic voltammetry experiments indicated that the catalytic process proceed via "one-site catalysis with two-sites oxidation" mechanism in which both two metal sites store the required oxidation equivalents for water oxidation and O-O bond formation occurs by single-site water nucleophilic attack(WNA).

One Stone Two Birds-Enantioselective Bimetallic Catalysis forα-Amino Acid Derivatives with an Allene Unit

Main observation and conclusion A highly enantioselective 2,3-allenylation of acyclic and cyclicα-imino carboxylates via a synergistic bimetallic Pd/Cu catalysis with the same commercially available(R,Rp)-iPr-FOXAP(also as Phosferrox,(R,R)-[2-(4’-i-propyloxazolin-2’-yl)ferrocenyl]diphenyl phosphine)ligand for both metals affording optically active 2,3-butadienylα-amino acid derivatives in high to excellent yields with excellent enantioselectivities has been developed.

Bimetallic anchoring catalysis for C–H and C–C activation

Following the age of directing group,anchoring catalysis starts coming to the center of the stage.Different from the directinggroup strategy that needs a preinstalled directing group in substrates,anchoring catalysis relies on a reversible interaction between a substrate and a catalyst,which then directs metal to activate inert chemical bonds.Such reversible directing effect not only generates good site-and stereo-selectivity as traditional directing groups do but also eliminates the requirement of stoichiometric amounts of directing groups.Among variously reported anchoring catalysis,coordinative bimetallic anchoring catalysis in general displays superior reactivity than others because coordinative bonding not only affords strong interaction of catalysts with substrates but also displays good compatibility with substrates and reaction conditions.In recent years,big progress has been achieved for coordinative bimetallic anchoring catalysis.This review gave a detailed summary of this field,including catalyst development,catalyst types,reaction types and reaction mechanisms.

Stereodivergent Benzylic Substitution of Racemic Secondary Benzyl Esters Enabled by Pd/Cu Dual Catalysis

Transition-metal-catalyzed asymmetric benzylic substitution of racemic benzyl esters is an efficient and straightforward route towards the construction of benzylic stereocenters but remains a challenge,due to the difficulty encountered in the suppression ofβ–H elimination and asymmetric induction.Herein,we successfully developed a highly diastereo-and enantioselective benzylic substitution of racemic 1-(aryl)alkyl esters with aldimine esters enabled by Pd/Cu dual catalysis.An array of enantioenrichedα-benzyl substitutedα-amino acids containing vicinal stereocenters were prepared with high levels of diastereo-and enantioselectivities(up to>20:1 dr and>99%ee)and the practicability of the products was further illustrated via their diverse transformations.The dynamic kinetic asymmetric transformation process of the racemic benzyl esters was investigated experimentally and by computational studies.

Direct Synthesis of Dimethyl Carbonate from CO_2 and CH_3OH Using 0.4nm Molecular Sieve Supported Cu-Ni Bimetal Catalyst

The 0.4 nm molecular sieve supported Cu-Ni bimetal catalysts for direct synthesis of dimethyl carbonate (DMC) from CO 2 and CH 3 OH were prepared and investigated. The synthesized catalysts were fully characterized by BET, XRD (X-ray diffraction), TPR (temperature programmed reduction), IR (infra-red adsorption), NH 3-TPD (temperature programmed desorption) and CO 2-TPD (temperature programmed desorption) techniques. The results showed that the surface area of catalysts decreased with increasing metal content, and the metals as well as Cu-Ni alloy co-existed on the reduced catalyst surface. There existed interaction between metal and carrier, and moreover, metal particles affected obviously the acidity and basicity of carrier. The large amount of basic sites facilitated the activation of methanol to methoxyl species and their subsequent reaction with activated carbon dioxide. The catalysts were evaluated in a continuous tubular fixed-bed micro-gaseous reactor and the catalyst with bimetal loading of 20% (by mass) had best catalytic activities. Under the conditions of 393 K, 1.1 MPa, 5 h and gas space velocity of 510 h 1 , the selectivity and yield of DMC were higher than 86.0 % and 5.0 %, respectively.

Asymmetric Transfer Hydrogenation of Naphthol and Phenol Derivatives with Cooperative Heterogeneous and Homogeneous Catalysis

Asymmetric hydrogenation of all-carbon aromatics is still a long-standing challenge in the area of asymmetric catalysis.To date,asymmetric(transfer)hydrogenation of naphthols and phenols remains unexplored.Here,we describe a new strategy for such asymmetric transformation via a bimetallic cooperative heterogeneous and homogeneous catalysis.By using HCOONa as the hydrogen source,various naphthols and phenols were partially hydrogenated in HFIP catalyzed by commercial Pd/C catalyst to give ketone intermediates.Further adding the second chiral Ru-tethered-TsDPEN catalyst and MeOH realized the asymmetric reduction of the resulting ketones in a one-pot manner,furnishing chiral alcohols with good to excellent enantioselectivity(up to 99%ee).The use of HFIP is crucial for suppressing ketone over-reduction via heterogeneous catalysis.More importantly,tandem asymmetric transfer hydrogenation of naphthols was also achieved by tuning the volume ratio of mixed HFIP/MeOH solvent,affording chiral 1,2,3,4-tetrahyronaphthols with excellent enantioselectivity but relatively low yield and limited substrate scope.

Synergistic catalysis for stereocontrol of prochiral nucleophiles in palladium-catalyzed asymmetric allylic substitution

In contrast to the stereocontrol of the stereocenter at the allyl unit,the asymmetric induction of prochiral nucleophiles remains a challenge in Pd-catalyzed asymmetric allylic substitutions due to the remote distance between the chiral catalyst and the stereocenter established at prochiral nucleophile.Much effort has been devoted to solving this challenge through the elaborate design of chiral ligands.Recently,synergistic catalysis has gained increasing attention owing to its potential advantages over the traditional single palladium catalysis,such as improvement of reactivity and selectivity.This strategy,including bimetallic catalysis and Pd/organocatalysis,not only broadens the scope of prochiral nucleophiles,but also provides a simple and unified method for the stereocontrol of prochiral nucleophiles.This review summarizes the brief history and advances in this field.

Stereodivergent Pd/Cu Catalysis for Asymmetric Desymmetric Alkylation of Allylic Geminal Dicarboxylates

AstereodivergentPd/Cucatalyst systemforasymmetric desymmetric alkylation of allylic geminal dicarboxylates has been developed,which was successfully applied to the asymmetric synthesis of β-hydroxycarbonylmotifs bearing a versatile carbon-carbon double bond in an enantio-and diastereodivergent manner.A wide scope of substrates including challenging alkylsubstituted,2-substituted,and3,3′-disubstitutedallylic species are compatible with this catalytic system,delivering the substituted products in high to excellent yieldsandwith excellent diastereo-(upto>20:1 dr)and enantioselectivities(up to>99%ee).Furthermore,the mechanism of this dual Pd/Cu catalytic system including:(1)the desymmetrization process ofgeminal dicarboxylates;(2)the origin of regioselectivity(branched or linear);(3)the enantio-and diastereoselectivity observed by changing the combinations of two chiral metal catalysts,have been carefully investigated by theoretical calculations.

Development of sterically hindered SPOs and enantioselective Ni-Al bimetallic catalyzed C-H cyclization of 4-oxoquinazolines with tethered alkenes

The Ni-Al bimetallic catalysis of intramolecular enantioselective and regioselective C-H cyclization of4-oxoquinazolines with tethered alkenes has been successfully developed.Some new secondary phosphine oxides(SPOs)with large steric hindrance(SPO6-11)were designed and successfully synthesized from readily available chiral amines or amino acids.The developed chiral SPOs as ligands or preligands demonstrate much higher efficiency in the asymmetric catalytic reactions than the reported traditional ones.A new class of chiral tricyclic pyrroloquinazolinones were obtained in up to 95%yield and 99%ee.

Overriding the inherent alkalinity to dual phosphinito bimetallic catalyst for C(sp^(2))-C(sp^(3))formation:A combined computational and experimental study

Unraveling the catalytic reaction mechanism is a long-term challenge for developing efficient catalysts.The blooming bimetallic catalyst have enabled to activate inert bonds and realize complex C-C formation.Herein,we theoretically discover a dual-phosphinito bridged hetero-bimetallic species that verified by NMR experiments.Our results indicate only dual-phosphinito Ni-Al model can be an active catalyst in asymmetric cycloadditions via C-C activation and C-H activation,which can well rationalize the experimental observations for both reactivity and stereo-selectivity.An unprecedented tandem redox dehydrogenation mechanism was revealed to control the formation of this active species overriding the inherent basicity.Synergistic Lewis acid and eg orbital interactions,including dz2 orbital reoccupation and d_(x^(2)−y^(2))orbital recombination,were disclosed to understand both thermodynamic and kinetic advance of dual-bridged model,displaying feasible redox properties.

Atomically Dispersed Pt and NiO Clusters Synergistically Enhanced C–O Bond Hydrogenolysis

C–Obond activation is a highly efficient,fundamental strategy in the depolymerization and hydrodeoxygenation of chemicals with oxygen-containing functional groups such as oil,coal,and biomass.Developing efficient catalysts for C–Oactivation with ultralow-loading noble and non-noble metals is highly desirable for the improvement of metal atomic utilization.Herein,bimetallic catalysts with atomically dispersed Pt and NiO clusters on different supports were fabricated,and the prepared Pt^(δ+)-NiO/Nb_(2)O_(5)and Pt^(δ+)-NiO/TiO_(2)showed outstanding activity for the hydrogenolysis of benzyl phenyl ether with>99%yield of phenol and toluene due to the excellent cooperation of atomically dispersed Pt and NiO clusters.The synergy mechanism between Pt and Ni and their respective roles in the bimetallic catalyst for C–O hydrogenolysis were clearly clarified.These findings deepen our understanding of the synergy of the two active components and are expected to provide new design concepts for the development of multicomponents catalysts.

Direct synthesis of hydrogen peroxide on Pd nanosheets with edge decorated by Au nanoparticles

Direct synthesis of hydrogen peroxide from hydrogen and oxide(DSHP)is considered as a green pathway for H2O2 production because of the simple reaction route and 100%theoretical atom efficiency.Here,1.5 wt%Pd and 0.5 wt%Au were loaded on HZSM-5 nanosheets through sequential isovolumetric impregnation.TEM images and CO-TPD curves showed that Pd nanosheets were successfully synthesized between HZSM-5 nanosheets under zeolite confinement effect,and Au particles were loaded on the edge of Pd nanosheets and formed a structure that Pd nanosheets with edge decorated by Au nanoparticles(Au–Pd/ZN).The results showed that the selectivity for H2O2 could be reached around 60%in a 30 min reaction and the initial H2O2 productivity could reach 338.5 mmol gcat1 h1 on the Au–Pd/ZN catalyst.The enhanced selectivity and productivity could be related with high content of terrace sites and Au particles on the step sites of bimetallic nanosheets,in which both the terrace sites and the step sites replaced by Au particles showed higher dissociation activation energy for breaking the O–O bond than traditional step sites on Pd particles,inhibited the by-product reactions(2H2O2→2H2OþO2,2H2þO2→2H2O).