Heterobimetallic Catalysts Research Articles

Hydrogenation Reactions with Heterobimetallic Complexes

AbstractHydrogenations are fundamentally and industrially important reactions that are atom economical paths to synthesize value‐added products from feedstock chemicals. The cooperative effects of two or more metal centers in multimetallic active sites is a successful strategy to activate small molecules and facilitate catalytic reactions, and this strategy has been recently applied to catalytic hydrogenation reactions. Furthermore, heterobimetallic complexes have been well‐documented to provide novel reaction pathways and improved selectivity, compared to their homo‐bimetallic and monometallic analogues. This minireview provides a historical perspective on the development of heterobimetallic catalysts for the hydrogenation of unsaturated substrates and describes recent developments in this burgeoning research area.

Mechanism and chemoselectivity of nitrile hydrosilylation catalyzed by [E-Rh] (E=Al, Ga, In) heterobimetallic catalysts: A theoretical perspective

Transition metals catalyzed hydrosilylation reaction is of significant values in organic synthesis. Herein the detailed mechanisms of the phenylacetonitrile hydrosilylation catalyzed by bimetallic [E-Rh] (E=Al, Ga, In) catalysts, as well as the RhCl(PPh3)3 monometallic catalyst, were investigated by DFT calculations. The electronic structure analysis indicates that the different atomic contributions of the Rh atom in E-Rh bond result in the polarity variations of the metal-metal bonds and different catalytic activities. The whole catalyzed cycle involves five processes: the formation of rhodium hydride complex, activation of H2SiMe2, insertion of phenylacetonitrile, reductive elimination, and isomerization. The reaction activities of [E-Rh] (E=Al, Ga, In) decrease successively, which is in agreement with the atomic contributions of Rh in three catalysts. DI analysis provides the evidence that the catalytic activity is controlled by the distortion energy of rate-determining state. QTAIM analysis shows the transformation of the Cl atom between two metal atoms, providing a clear description for structural changes in catalytic cycle.

Hydrogenation Reactions with Heterobimetallic Complexes.

Hydrogenations are fundamentally and industrially important reactions that are atom economical paths to synthesize value-added products from feedstock chemicals. The cooperative effects of two or more metal centers in multimetallic active sites is a successful strategy to activate small molecules and facilitate catalytic reactions, and this strategy has been recently applied to catalytic hydrogenation reactions. Furthermore, heterobimetallic complexes have been well-documented to provide novel reaction pathways and improved selectivity, compared to their homo-bimetallic and monometallic analogues. This minireview provides a historical perspective on the development of heterobimetallic catalysts for the hydrogenation of unsaturated substrates and describes recent developments in this burgeoning research area.

Weak Bimetal Coupling-Assisted MN4 Catalyst for Enhanced Carbon Dioxide Reduction Reaction.

The design of multimetal catalysts holds immense significance for efficient CO2 capture and its conversion into economically valuable chemicals. Herein, heterobimetallic catalysts (MiMo)L were exploited for the CO2 reduction reactions (CO2RR) using relativistic density functional theory (DFT). The octadentate Pacman-like polypyrrolic ligand (H4L) accommodates two metal ions (Mo, W, Nd, and U) inside (Mi) and outside (Mo) its month, rendering a weak bimetal coupling-assisted MN4 catalytically active site. Adsorption reactions have access to energetically stable coordination modes of -OCO, -OOC, and -(OCO)2, where the donor atom(s) are marked in bold. Among all of the species, (UiMoo)L releases the most energy. Along CO2RR, it favors to produce CO. The high-efficiency CO2 reduction is attributed to the size matching of U with the ligand mouth and the effective manipulation of the electron density of both ligand and bimetals. The mechanism in which heterobimetals synergetically capture and reduce CO2 has been postulated. This establishes a reference in elaborating on the complicated heterogeneous catalysis.

Bimetallic Molecular Catalyst Design for Carbon Dioxide Reduction.

The core challenge in developing cost-efficient catalysts for carbon dioxide (CO2 ) conversion mainly lies in controlling its complex reaction pathways. One such strategy exploits bimetallic cooperativity, which relies on the synergistic interaction between two metal centers to activate and convert the CO2 substrate. While this approach has seen an important trend in heterogeneous catalysis as a handle to control stabilities of surface intermediates, it has not often been utilized in molecular and heterogenized molecular catalytic systems. In this review, we gather general principles on how natural CO2 activating enzymes take advantage of bimetallic strategy and how phosphines, cyclams, polypyridyls, porphyrins, and cryptates-based homo- and hetero-bimetallic molecular catalysts can help understand the synergistic effect of two metal centers.

Mechanism determination on [LCu-Fp] heterobimetallic-catalyzed C-H borylation of benzene and regioselectivity regulation: A DFT investigation

The heterobimetallic complex [(NHC)Cu-FeCp(CO)2] ([LCu-Fp]) is an efficient and sustainable catalyst for C-H borylation under UV light irradiation, whereas the catalytic mechanism is still debating. One opinion is the thermal induced mechanism, in which Cu-Fe bond in [LCu-Fp] firstly dissociated by B-H activation, and then induced the decarbonylation of FpBpin by UV irradiation. The other is the UV-induced mechanism, the decarbonylation of [LCu-Fp] occurred before the Cu-Fe broken. In this work, detailed mechanism of UV-induced has been investigated by DFT calculations and compared with the thermal induced mechanism. Our calculated results show that both of them can occur under UV light irradiation at room temperature. The UV-induced mechanism contains four steps: CO dissociation, Cu-Fe bond breakage by B-H activation, C-H borylation, and H-H reductive elimination. In the last step, it is the re-coordination of CO to the Fe occurs before the releasing of H2. The strong election-withdrawing substituent of benzene would increase the yield of para-product, whereas the election-donating substituent has little influence on the regioselectivity. Our calculation determines the detail mechanism of the title reaction and provides reasonable explanation for the regioselectivity of C-H borylation of substituted benzene, which would help for the widely usages of the heterobimetallic catalysts.

Therapeutic N-heterocyclic carbenes: an interview with Alejandro Bugarin.

DrBugarin is currently an Associate Professor of Chemistry and Physics at Florida Gulf Coast University. He has published more than 50 peer-reviewed publications (h-index = 18). His research group is developing newmethodology to improve or reveal novel reactivity of triazenes, N-Heterocyclic carbenes, heterobimetallic catalysts, and other versatile molecules. In addition, he recently joined research efforts to build on theisolation, characterization, and biological evaluation of natural products.

Engineering regioselectivity in the hydrosilylation of alkynes using heterobimetallic dual-functional hybrid catalysts

The synthesis and characterization of carbon black supported rhodium and iridium heterobimetallic hybrid catalysts and their application in the hydrosilylation of alkynes is described.

Heterometallic cooperativity in divalent metal ProPhenol catalysts: combining zinc with magnesium or calcium for cyclic ester ring-opening polymerisation

The first heterobimetallic lactide ROP catalysts based on two divalent metals outperform the homobimetallic analogues, attributed to the increased Lewis acidity of Mg or Ca (monomer coordination) and enhanced polarity of Zn–Et/OR (propagation).

Control of the Regioselectivity of Alkyne Hydrostannylation by Tuning the Metal Pair of Heterobimetallic Catalysts: A Theoretical Study

In this work, the detailed reaction mechanisms of two distinct Sn–H bond activation modes of the [Cu–Fe] and [Cu–Mn] heterobimetallic catalysts were computationally investigated using density funct...

Cooperative Heterometallic Catalysts for Lactide Ring-Opening Polymerization: Combining Aluminum with Divalent Metals.

While homometallic (salen)Al catalysts display excellent performance in lactide ring-opening polymerization (ROP), heterometallic (salen)Al complexes have yet to be reported. Herein, we describe four heterobimetallic (salen)Al catalysts and show that the choice of the heterometal is key. Cooperative Al/Mg and Al/Zn combinations improved the catalyst activity by a factor of up to 11 compared to the mono-Al analogue, whereas the mono-Mg and mono-Zn analogues were completely inactive. In contrast, Al/Li and Al/Ca heterocombinations stunted the polymerization rate. Kinetic and computational studies suggest that Al/Mg and Al/Zn cooperativity arises from the close intermetallic proximity facilitating chloride bridging (thus enhancing initiation), which promotes a rigid square pyramidal geometry around the Al center and further increases the available monomer coordination sites. This work also translates the use of ab initio molecular dynamics calculations to ROP, introducing a useful method of investigating catalyst flexibility and revealing that ligand strain and molecular rigidity can enhance heterometallic catalyst performance.

Catalytic Reactions by Heterobimetallic Carbonyl Complexes with Polar Metal–Metal Interactions

AbstractHeterobinuclear catalysts capable of bimetallic cooperative bond activation provide an alternative pathway to approach the discovery of novel and unique reactivity and selectivity in catalytic transformations, complementing more traditional mononuclear precious metal catalysts. This review summarizes recent advances in homogenous catalysis using heterobimetallic carbonyl catalysts with polar metal–metal interactions.1 Introduction2 Hydrogenation and Hydrofunctionalization3 Carbonylation and Carboxylation4 Oxidative Transformations5 Conclusion and Outlook

Heterobimetallic Catalysts for the Thermal Decomposition of Ammonium Perchlorate: Efficient Burning Rate Catalysts for Solid Rocket Motors and Missiles

We show the synthesis and characterization of four heterobimetallic compounds derived from s-indacene of general formula [{(CO)3Mn}-s-Ic-{MCp*}]q with M = Fe, Co, Ni, and Ru; q = 0, 1+. The complexes reported here were characterized by 1H and 13C NMR, elemental analysis and FT-IR. Additionally, the X-ray crystal structure of [(CO)3Mn-s-Ic-FeCp*] (1) and Mössbauer spectra are reported. The heterobimetallic compounds exhibit higher quasireversible redox potentials compared with ferrocene and catocene under the same reaction conditions. The complexes were tested as catalysts on the thermal decomposition of ammonium perchlorate examined by a differential scanning calorimetry technique to study their catalytic behavior. Compound (1) causes a decrease of ammonium perchlorate's decomposition temperature to 315 °C, consequently increasing the heat release by 138 J·g-1. Conversely, [{(CO)3Mn}-s-Ic'-{CoCp*}] (2) presents a higher heat release (2462 J·g-1), comparable to catocene.

Pursuit of C–H Borylation Reactions with Non-Precious Heterobimetallic Catalysts: Hypothesis-Driven Variations on a Design Theme

This article presents a retrospective account of our group’s heterobinuclear (NHC)Cu-[MCO] catalyst design concept (NHC = N-heterocyclic carbene, [MCO] = metal carbonyl anion), the discovery of its application towards UV-light-induced dehydrogenative borylation of unactivated arenes, and the subsequent pursuit of thermal reaction conditions through structural modifications of the catalysts. The account highlights advantages of using a hypothesis-driven catalyst design approach that, while often fruitless with regard to the target transformation in this case, nonetheless vastly expanded the set of heterobinuclear catalysts available for other applications. In other words, curiosity-driven research conducted in a rational manner often provides valuable products with unanticipated applications, even if the primary objective is viewed to have failed.1 Introduction to Heterobinuclear Catalysts for C–H Borylation2 Pursuit of Thermal Borylation Conditions3 Catalysts beyond Copper Carbenes4 Conclusions

Metal-Metal Synergy in Well-Defined Surface Tantalum-Iridium Heterobimetallic Catalysts for H/D Exchange Reactions.

A novel heterobimetallic tantalum/iridium hydrido complex, [{Ta(CH2tBu)3}{IrH2(Cp*)}] 1, featuring a very short metal-metal bond, has been isolated through an original alkane elimination route from Ta(CHtBu)(CH2tBu)3 and Cp*IrH4. This molecular precursor has been used to synthesize well-defined silica-supported low-coordinate heterobimetallic hydrido species [≡SiOTa(CH2tBu)2{IrH2(Cp*)}], 5, and [≡SiOTa(CH2tBu)H{IrH2(Cp*)}], 6, using a surface organometallic chemistry (SOMC) approach. The SOMC methodology prevents undesired dimerization as encountered in solution and leading to a tetranuclear species [{Ta(CH2tBu)2}(Cp*IrH)]2, 4. This approach therefore allows access to unique low-coordinate species not attainable in solution. These original supported Ta/Ir species exhibit drastically enhanced catalytic performances in H/D exchange reactions with respect to (i) monometallic analogues as well as (ii) homogeneous systems. In particular, material 6 promotes the H/D exchange between fluorobenzene and C6D6 or D2 as deuterium sources with excellent productivity (TON up to 1422; TOF up to 23.3 h-1) under mild conditions (25 °C, sub-atmospheric D2 pressure) without any additives.

Chiral Heterobimetallic Bismuth-Rhodium Paddlewheel Catalysts: A Conceptually New Approach to Asymmetric Cyclopropanation.

Cyclopropanation reactions of styrene derivatives with donor-acceptor carbenes formed in situ are significantly more enantioselective when catalyzed by the heterobimetallic bismuth-rhodium complex 5 a endowed with N-phthalimido tert-leucine paddlewheel ligands rather than by its homobimetallic dirhodium analogue 1 a. This virtue is likely the result of two synergizing factors: the conical shape of 5 a translates into a narrower calyx-like chiral binding site about the catalytically active Rh center; the Bi atom, although fully solvent exposed, does not decompose aryl diazoacetates and is hence incapable of promoting a racemic background reaction. Moreover, ligand variation proved that successful catalyst design mandates that the anisotropy of the conical heterobimetallic core be matched by proper directionality of the ligand sphere.

Heterogeneous Heterobimetallic Catalysis Enabling Expeditious Access to CF3-Containing vic-Amino Alcohols.

A highly anti-selective catalytic asymmetric nitroaldol reaction of trifluoromethyl ketones based on Nd/Na and Pr/Na heterobimetallic catalysts was developed. These catalysts function as heterogeneous catalysts to engage nitroethane and a range of trifluoromethyl ketones in a stereoselective assembly to afford CF3-appended vic-nitroalkanols that could be readily converted to enantioenriched vic-amino alcohols, which are privileged structural motifs in medicinal chemistry.

Customizing Polyolefin Morphology by Selective Pairing of Alkali Ions with Nickel Phenoxyimine-Polyethylene Glycol Catalysts

In the present work, we have prepared nickel phenoxyimine-polyethylene glycol (PEG) catalysts with sterically bulky N-aryl substituents and investigated their ethylene homo- and copolymerization behavior. We have found that different nickel catalyst and alkali ion (Na+ or K+) combinations yielded polyethylene with different branching microstructures and molecular weights. Our heterobimetallic catalysts can copolymerize ethylene and nonpolar α-olefins with high activity but are strongly inhibited in the presence of polar vinyl olefins. We demonstrate that our heterobimetallic catalysts are significantly more stable in ethylene homopolymerization in comparison to conventional nickel phenoxyimine systems on the basis of time-dependent activity studies. This work showcases the versatility of Lewis acid tunable catalyst constructs to prepare customized polyolefins and suggests that similar design strategies could be applied to other catalyst systems.

An Efficient Heterobimetallic Lanthanide Alkoxide Catalyst for Transamidation of Amides under Solvent‐Free Conditions

AbstractA practical heterobimetallic lanthanide‐catalyzed transamidation of primary, secondary and tertiary amides with aliphatic and aromatic amines has been developed. The methodology was also applied to the weakly reactive thioamides to demonstrate its versatility and wide substrate scope. The heterobimetallic lanthanide catalysts showed high catalytic activity and a wide scope of substrates with good to excellent yields under solvent‐free conditions. Efficient activation of the transamidation can be realized by the above complexes acting as cooperative acid–base bifunctional catalysts, which are proposed to be responsible for the higher reactivity in comparison with simple monometallic catalysts.magnified image

Driving the Oxygen Evolution Reaction by Nonlinear Cooperativity in Bimetallic Coordination Catalysts.

Developing efficient catalysts for electrolysis, in particular for the oxygen evolution in the anodic half cell reaction, is an important challenge in energy conversion technologies. By taking inspiration from the catalytic properties of single-atom catalysts and metallo-proteins, we exploit the potential of metal-organic networks as electrocatalysts in the oxygen evolution reaction (OER). A dramatic enhancement of the catalytic activity toward the production of oxygen by nearly 2 orders of magnitude is demonstrated for novel heterobimetallic organic catalysts compared to metallo-porphyrins. Using a supramolecular approach we deliberately place single iron and cobalt atoms in either of two different coordination environments and observe a highly nonlinear increase in the catalytic activity depending on the coordination spheres of Fe and Co. Catalysis sets in at about 300 mV overpotential with high turnover frequencies that outperform other metal-organic catalysts like the prototypical hangman porphyrins.