Immobilized Catalysts for Hydroformylation Reactions: A Versatile Tool for Aldehyde Synthesis

Enhancing stability via confining Rh-P species in ZIF-8 for hydroformylation of 1-octene

The stability of Rh-based heterogeneous catalysts is a key issue in the hydroformylation of olefins. Confinement of active Rh species has been considered an effective strategy to achieve stable catalysts. In this work, a phosphine ligand was successfully confined in ZIF-8 material and coordinated with Rh metal by a reduction procedure to develop an efficient and stable Rh-based catalyst for hydroformylation of 1-octene. The results indicate that the catalyst reduced at 300 °C under H2 atmosphere exhibits better stability than that with NaBH4 as reductant and undoped P catalyst. Various characterization studies demonstrate that the superior performance is due to the strong interaction between Rh metal and P, which inhibits the leaching of active Rh species. This work reveals an effective strategy for the synthesis of highly stable catalysts for use in the hydroformylation reaction.

Recent development towards alkene hydroformylation catalysts integrating traditional homo- and heterogeneous catalysis

This mini-review provides the recent progress towards catalysts for the hydroformylation of catalysts that bridge traditional homo- and heterogeneous catalysis, highlighting the future development of heterogeneous catalysts in hydroformylation.

Supramolecular Strategies for the Recycling of Homogeneous Catalysts

Supramolecular approaches are increasingly used in the development of homogeneous catalysts and they also provide interesting new tools for the recycling of metal-based catalysts. Various non-covalent interactions have been utilized for the immobilization homogeneous catalysts on soluble and insoluble support. By non-covalent anchoring the supported catalysts obtained can be recovered via (nano-) filtration or such catalytic materials can be used in continuous flow reactors. Specific benefits from the reversibility of catalyst immobilization by non-covalent interactions include the possibility to re-functionalize the support material and the use as "boomerang" type catalyst systems in which the catalyst is captured after a homogeneous reaction. In addition, new reactor design with implemented recycling strategies becomes possible, such as a reverse-flow adsorption reactor (RFA) that combines a homogeneous reactor with selective catalyst adsorption/desorpion. Next to these non-covalent immobilization strategies, supramolecular chemistry can also be used to generate the support, for example by generation of self-assembled gels with catalytic function. Although the stability is a challenging issue, some self-assembled gel materials have been successfully utilized as reusable heterogeneous catalysts. In addition, catalytically active coordination cages, which are frequently used to achieve specific activity or selectivity, can be bound to support by ionic interactions or can be prepared in structured solid materials. These new heterogenized cage materials also have been used successfully as recyclable catalysts.

Immobilization of Rh(I)-N-Xantphos and Fe(II)-C-Scorpionate onto Magnetic Nanoparticles: Reusable Catalytic System for Sequential Hydroformylation/Acetalization

Two heterogeneous catalysts, MNP@SiO2-N-Xantphos/Rh(I) and MNP@SiO2-NH-C-scorpionate/Fe(II), were prepared by reaction of chloro-functionalized MNP@SiO2 with N-Xantphos and amino-functionalized MNP@SiO2 with iron(II)/C-allyl-scorpionate through nucleophilic substitution and hydroaminomethylation reactions, respectively. All catalysts were characterized using standard spectroscopic means, transmission electron microscopy (TEM), thermogravimetry (TG), and inductively coupled plasma optical emission spectrometry (ICP-OES). An active and highly selective one-pot hydroformylation/acetalization homogeneous system for the transformation of terminal and highly substituted olefins (including terpenes) onto ethyl acetals is described. A synergic effect of bimetallic Rh(I)/P and Fe(II)/C-scorpionate catalysts is disclosed for the first time. The further sequential use of the heterogeneous catalysts, MNP@SiO2-N-Xantphos/Rh(I) and MNP@SiO2-NH-C-scorpionate/Fe(II) in hydroformylation/acetalization reactions allows the direct transformation of olefin onto ethyl acetals, keeping the activity and selectivity. Both catalysts were easily recovered by magnetic separation and reused with negligible loss of activity/selectivity, after six reutilization cycles.

Postsynthetic Metalated MOFs as Atomically Dispersed Catalysts for Hydroformylation Reactions

A manganese-based metal-organic framework with dipyrazole ligands has been metalated with atomically dispersed Rh and Co species and used as a catalyst for the hydroformylation of styrene. The Rh-based materials exhibited excellent conversion at 80 °C with complete chemoselectivity, high selectivity for the branched aldehyde, high recyclability, and negligible metal leaching.

Enhancing the stability of the Rh/ZnO catalyst by the growth of ZIF-8 for the hydroformylation of higher olefins

Hydroformylation of olefins is one of the most important industrial processes for aldehyde production. Therein, the leaching of active metals for heterogeneous catalysts is an important issue in the hydroformylation reaction, particularly for higher olefins to produce higher alcohols. Here, different Rh/ZnO catalysts with diverse ZnO as a support were investigated and a home-made ZnO₅₀ support was selected to prepare the Rh/ZnO₅₀@ZIF-8 core–shell structure catalyst, which was synthesized by the growth of ZIF-8 with ZnO₅₀ as the sacrificed template to afford Zn source. Compared with the Rh/ZnO₅₀ catalyst, the Rh/ZnO₅₀@ZIF-8 catalyst demonstrated a better cyclic stability in the hydroformylation of 1-dodecene. Combining the experiment and characterization results, it was concluded that the ZIF-8 shell on the Rh/ZnO₅₀ catalyst effectively prevented the leaching of metal Rh into the reaction solution. Moreover, the Rh/ZnO₅₀@ZIF-8 catalyst exhibited good universality for other higher olefins. This work provides a useful guideline for immobilizing the active species in heterogeneous catalysts for the hydroformylation reaction.

The stability of the Rh/ZnO catalyst in the hydroformylation of 1-dodecene obviously improved, which was attributed to that the ZIF-8 shell on the Rh/ZnO catalyst effectively prevented the leaching of metal Rh.

Current State of the Art of the Solid Rh-Based Catalyzed Hydroformylation of Short-Chain Olefins

The hydroformylation of olefins is one of the most important homogeneously catalyzed processes in industry to produce bulk chemicals. Despite the high catalytic activities and selectivity’s using rhodium-based homogeneous hydroformylation catalysts, catalyst recovery and recycling from the reaction mixture remain a challenging topic on a process level. Therefore, technical solutions involving alternate approaches with heterogeneous catalysts for the conversion of olefins into aldehydes have been considered and research activities have addressed the synthesis and development of heterogeneous rhodium-based hydroformylation catalysts. Different strategies were pursued by different groups of authors, such as the deposition of molecular rhodium complexes, metallic rhodium nanoparticles and single-atom catalysts on a solid support as well as rhodium complexes present in supported liquids. An overview of the recent developments made in the area of the heterogenization of homogeneous rhodium catalysts and their application in the hydroformylation of short-chain olefins is given. A special focus is laid on the mechanistic understanding of the heterogeneously catalyzed reactions at a molecular level in order to provide a guide for the future design of rhodium-based heterogeneous hydroformylation catalysts.

Catalytic isomerization–hydroformylation of olefins by rhodium salicylaldimine pre-catalysts

A series of new Schiff-base rhodium(i) water-soluble complexes (C1–C3), were prepared and characterized.

Recent Advances Utilized in the Recycling of Homogeneous Catalysis

Homogeneous catalysts often show high activity and selectivity towards the various chemical transformations. Most of the transition metal-based active catalysts are expensive, rare, and have strict regulations for their use in pharmaceutical products. Hence, there is a requirement to develop suitable technologies for the practical separation and recycling of metal complex catalysts along with the sustainability of the process. This review focuses on the recent techniques used for the catalyst separation, their recovery, and recyclability of the homogeneous form of catalysts based on their economic compatibility and industrial applications. Various homogeneous catalysts have been reviewed on the basis of their support or media, active centres and recyclability aspects of the catalysts. This review gives brief insights into the varied examples of different recycling techniques utilized in the past 6-7 years.

Synthesis and Characterization of Rh/B⁻TNTs as a Recyclable Catalyst for Hydroformylation of Olefin Containing ⁻CN Functional Group

The TiO₂-based nanotubes (TNTs, B⁻TNTs) of different surface acidities and their supported Rh catalysts were designed and synthesized. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectrometer (XPS), tempera⁻ture⁻programmed desorption of ammonia (NH₃⁻TPD), atomic emission spectrometer (ICP), and Brunauer⁻Emmett⁻Tellerv (BET) surface-area analyzers. Images of SEM and TEM showed that the boron-decorated TiO₂ nanotubes (B⁻TNTs) had a perfect multiwalled tubular structure; their length was up to hundreds of nanometers and inner diameter was about 7 nm. The results of NH₃-TPD analyses showed that B⁻TNTs had a stronger acid site compared with TNTs. For Rh/TNTs and Rh/B⁻TNTs, Rh nanoparticles highly dispersed on B⁻TNTs were about 2.79 nm in average diameter and much smaller than those on TNTs, which were about 4.94 nm. The catalytic performances of catalysts for the hydroformylation of 2-methyl-3-butennitrile (2M3BN) were also evaluated, and results showed that the existence of B in Rh/B⁻TNTs had a great influence on the catalytic performance of the catalysts. The Rh/B⁻TNTs displayed higher catalytic activity, selectivity for aldehydes, and stability than the Rh/TNTs.

New Heterogeneous Rh-Containing Catalysts Immobilized on a Hybrid Organic-Inorganic Surface for Hydroformylation of Unsaturated Compounds

Anchoring Rh complexes to the surface of a silica polyamine composite, which has a poly(allylamine) covalently grafted to the surface of amorphous silica gel, yielded a material that proved to be an effective and novel heterogeneous catalyst for hydroformylation of unsaturated compounds. Surface amino groups of the material were modified with phosphines by covalent and ionic coupling. The modified materials were then treated with Rh(acac)(CO)₂, giving the catalysts K-1 and K-2. Catalysts were characterized by solid-state NMR spectroscopy, IR spectroscopy, XPS, TEM, and elemental analysis. The activity and stability of K-1 and K-2 were then studied for the hydroformylation of selected unsaturated compounds. Hydroformylation of terminal double bonds occurred selectively in the presence of internal double bonds. Characterization of the catalysts and the problems encountered with the supported catalysts are discussed. Catalyst K-1 is reusable and can be applied to the hydroformylation of linear olefins, styrene, 4-vinylcyclohexene, and dienes, as well as representative terpenes and other unsaturated hydrocarbons in a batch reactor.

Platinum Group Metal Phosphides as Efficient Catalysts in Hydroprocessing and Syngas-Related Catalysis

Platinum group metal phosphides are reviewed as catalytic materials for hydroprocessing and syngas-related catalysis. Starting from synthetic procedures leading to highly disperse nano-particular compounds, their properties in the applications are discussed and compared with relevant benchmarks, if available. Regarding their mode of action, two confronting mechanistic scenarios are presented: (i) a cooperative scenario in which catalytic sites of different functionalities are active in hydroprocessing and (ii) single site catalysis, which appears to be the relevant mode of action in syngas-related catalysis and which occurs over “frustrated” active sites.

Atomic-level insights in optimizing reaction paths for hydroformylation reaction over Rh/CoO single-atom catalyst

Rh-based heterogeneous catalysts generally have limited selectivity relative to their homogeneous counterparts in hydroformylation reactions despite of the convenience of catalyst separation in heterogeneous catalysis. Here, we develop CoO-supported Rh single-atom catalysts (Rh/CoO) with remarkable activity and selectivity towards propene hydroformylation. By increasing Rh mass loading, isolated Rh atoms switch to aggregated clusters of different atomicity. During the hydroformylation, Rh/CoO achieves the optimal selectivity of 94.4% for butyraldehyde and the highest turnover frequency number of 2,065 h^-1 among the obtained atomic-scale Rh-based catalysts. Mechanistic studies reveal that a structural reconstruction of Rh single atoms in Rh/CoO occurs during the catalytic process, facilitating the adsorption and activation of reactants. In kinetic view, linear products are determined as the dominating products by analysing reaction paths deriving from the two most stable co-adsorbed configurations. As a bridge of homogeneous and heterogeneous catalysis, single-atom catalysts can be potentially applied in other industrial reactions.

New tetraphosphite ligands for regioselective linear hydroformylation of terminal and internal olefins

We successfully developed new tetraphosphite ligands L1–L5 and applied them to the rhodium-catalyzed hydroformylation of terminal and internal olefins.

Formylation of electron-rich aromatic rings mediated by dichloromethyl methyl ether and TiCl4: scope and limitations

Here the aromatic formylation mediated by TiCl4 and dichloromethyl methyl ether previously described by our group has been explored for a wide range of aromatic rings, including phenols, methoxy- and methylbenzenes, as an excellent way to produce aromatic aldehydes. Here we determine that the regioselectivity of this process is highly promoted by the coordination between the atoms present in the aromatic moiety and those in the metal core.

Synthesis of highly dispersed cobalt catalyst for hydroformylation of 1-hexene

A highly dispersed Co–Ru/SiO₂(EG) catalyst, prepared by surface modification of a silica support, exhibited significantly high activity and yield of oxygenates in 1-hexene hydroformylation.

Immobilization of imidazolium ionic liquids on hydrotalcites using silane linkers: retardation of memory effect

We report a new covalent surface immobilization of silane-modified imidazolium ionic liquids on hydrotalcite-like materials (HTs) and provide detailed characterization of the resulting surface chemistry using PXRD, CP-MAS, TGA and FT-IR.

An efficient heterogenized palladium catalyst for N-alkylation of amines and α-alkylation of ketones using alcohols

Silica supported palladium–NiXantphos complex is an efficient and high turnover heterogeneous catalyst for N-alkylation of amines and α-alkylation of ketones using alcohols under neat conditions at 120–140 °C following hydrogen borrowing strategy.