A General and Efficient Iridium‐Catalyzed Hydroformylation of Olefins

Highly (regio)selective hydroformylation of olefins using self-assembling phosphines

New phosphines with self-assembling 6-pyridinone moities were prepared, characterized, and examined in the hydroformylation of diverse olefins. Testing various known and novel ligands in the presence of [Rh(acac)(CO)2] under industrially relevant conditions, the hydroformylation of 1-octene proceeds best with 6,6'-(phenylphosphanediyl)bis(pyridin-2(1H)-one) (DPONP). Control experiments and modelling studies indicate dimerization of this ligand at higher temperatures (>100 °C). The optimal catalyst system is able to conserve high product linearity (>90%) for a broad range of olefins at industrially-employed temperatures at low ligand loading.

P(V)-Promoted Rh-Catalyzed Highly Regioselective Hydroformylation of Styrenes under Mild Conditions

Hydroformylation of olefins is widely used in the chemical industry due to its versatility and the ability to produce valuable aldehydes with 100% atom economy. Herein, a hybrid phosphate promoter was found to efficiently promote rhodium-catalyzed hydroformylation of styrenes under remarkably mild conditions with high regioselectivities. Preliminary mechanistic studies revealed that the weak coordination between the Rhodium and the P=O double bond of this pentavalent phosphate likely induced exceptional reactivity and high ratios of branched aldehydes to linear products.

Substrate scope driven optimization of an encapsulated hydroformylation catalyst

Caged complexes can provide impressive selective catalysts. Due to the complex shapes of such caged catalysts, however, the level of selectivity control of a single substrate cannot be extrapolated to other substrates. Herein, the substrate scope using 41 terminal alkene substrates is investigated in the hydroformylation reaction with an encapsulated rhodium catalyst [Rh(H)(CO)3(P(mPy3(ZnTPP)3))] (CAT1). For all substrates, the amount of branched products formed was higher with CAT1 than with the unencapsulated reference catalyst [Rh(H)(CO)2(P(mPy3))2] (CAT2) (linear/branched ratio between 2.14 and 0.12 for CAT1 and linear/branched ratio between 6.22 and 0.59 for CAT2). Interestingly, the level of cage induced selectivity depends strongly on the substrate structure that is converted. Analysis of the substrate scope combined with DFT calculations suggests that noncovalent interactions between the substrate moieties and cage walls play a key role in controlling the regioselectivity. Consequently, these supramolecular interactions were further optimized by replacing the ZnTPP building block with a zinc porphyrin analog that contained OiPr substituents on the meta position of the aryl rings. The resulting caged catalyst, CAT4, converted substrates with even higher branched selectivity.

Solvent-Controllable C-F Bond Activation for Masked Formylation of α-Trifluoromethyl Alkenes via Organo-Photoredox Catalysis

A solvent-controllable organo-photoredox-catalyzed C-F bond activation for masked formylation of α-trifluoromethyl alkenes with low-priced 1,3-dioxolane as masked formyl radical equivalent has been described. Consequently, a diversity of masked formylated gem-difluoroalkenes and monofluoroalkenes are constructed in moderate to high yields. This approach merits readily available starting materials, mild reaction conditions, and broad substrate scope. The feasibility of this approach has been highlighted by the one-pot masked formylation/hydrolysis sequence to form γ,γ-difluoroallylic aldehydes and late-stage modification of pharmaceutical and natural product derivatives.

Iridium-phosphine ligand complexes as an alternative to rhodium-based catalysts for the efficient hydroformylation of propene

Expensive rhodium (Rh)-based catalysts have been widely used for the hydroformylation of propene. To find a cheaper and effective alternative to these Rh-based catalysts, herein, a series of phosphine ligands were used to coordinate with iridium, and their catalytic reactivities for the hydroformylation of propene were systematically investigated in this study. The effects of different phosphine ligands, pressures, temperatures, and catalyst dosages on the hydroformylation of propene were investigated. Tripyridyl phosphine iridium Ir2(cod)2Cl2-P(3-py)3 (Ir(I)-L5) and its derivatives exhibit the highest catalytic reactivity. Surprisingly, the catalytic reactivity of Ir(I)-L5 is higher than that of Rh2(cod)2Cl2-P(3-py)3 (Rh(I)-L5). When the Ir(I)-L5 complex is used as the catalyst, reactions performed in a polar solvent gave higher turnover number (TON) values than those in a non-polar solvent. Up to a TON of 503 can be obtained. Different n-butyraldehyde/iso-butyraldehyde (n/i) ratios can be obtained by adjusting the phosphine ligands or the proportion of gas pressure. The catalyst showed good reusability in five recycling experiments. Furthermore, based on DFT theoretical calculations, a probable reaction mechanism was proposed. It is reliable that an Ir-based catalyst can be considered as a highly effective catalyst for the hydroformylation of propylene with CO.

Iridium-catalyzed Domino Hydroformylation/Hydrogenation of Olefins to Alcohols: Synergy of Two Ligands

A novel one‐pot iridium‐catalyzed domino hydroxymethylation of olefins, which relies on using two different ligands at the same time, is reported. DFT computation reveals different activities for the individual hydroformylation and hydrogenation steps in the presence of mono‐ and bidentate ligands. Whereas bidentate ligands have higher hydrogenation activity, monodentate ligands show higher hydroformylation activity. Accordingly, a catalyst system is introduced that uses dual ligands in the whole domino process. Control experiments show that the overall selectivity is kinetically controlled. Both computation and experiment explain the function of the two optimized ligands during the domino process.

One step synthesis of efficient photocatalysts by TCAP doped g-C3N4 for enhanced visible-light photocatalytic activity

CN/TCAP with enhanced visible light absorption, large surface area and defect structure allow efficient separation of charge carriers.

Synthesis of α,β-unsaturated carbonyl compounds by carbonylation reactions

Carbonylation reactions represent one of the most important tool box for the synthesis of α,β-unsaturated carbonyl compounds which are key building blocks in organic chemistry. This paper summarizes the most important advances in this field.

Efficient methanol carbonylation to methyl acetate catalyzed by a cyclic(alkyl)(amino)carbene iridium complex

An efficient cyclic(alkyl)(amino) carbene iridium complex (C-2) was developed for methanol carbonylation to methyl acetate (MA) directly.

Using para hydrogen induced polarization to study steps in the hydroformylation reaction

A range of iridium complexes, Ir(η3-C3H5)(CO)(PR2R')2 (1a-1e) [where 1a, PR2R' = PPh3, 1b P(p-tol)3, 1c PMePh2, 1d PMe2Ph and 1e PMe3] were synthesized and their reactivity as stoichiometric hydroformylation precursors studied. Para-hydrogen assisted NMR spectroscopy detected the following intermediates: Ir(H)2(η3-C3H5)(CO)(PR2R') (2a-e), Ir(H)2(η1-C3H5)(CO)(PR2R')2 (4d-e), Ir(H)2(η1-C3H5)(CO)2(PR2R') (10a-e), Ir(H)2(CO-C3H5)(CO)2(PR2R') (11a-c), Ir(H)2(CO-C3H7)(CO)2(PR2R') (12a-c) and Ir(H)2(CO-C3H5)(CO)(PR2R')2 (13d-e). Some of these species exist as two geometric isomers according to their multinuclear NMR characteristics. The NMR studies suggest a role for the following 16 electron species in these reactions: Ir(η3-C3H5)(CO)(PR2R'), Ir(η1-C3H5)(CO)(PR2R')2, Ir(η1-C3H5)(CO)2(PR2R'), Ir(CO-C3H5)(CO)2(PR2R'), Ir(CO-C3H7)(CO)2(PR2R') and Ir(CO-C3H5)(CO)(PR2R')2. Their role is linked to several 18 electron species in order to confirm the route by which hydroformylation and hydrogenation proceeds.

Preparation and Characterization of Rh/MgSNTs Catalyst for Hydroformylation of Vinyl Acetate: The Rh0 was Obtained by Calcination

A simple and practical Rh-catalyzed hydroformylation of vinyl acetate has been synthesized via impregnation-calcination method using silicate nanotubes (MgSNTs) as the supporter. The Rh0 (zero valent state of rhodium) was obtained by calcination. The influence of calcination temperature on catalytic performance of the catalysts was investigated in detail. The catalysts were characterized in detail by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectrometer (XPS), atomic emission spectrometer (ICP), and Brunauer–Emmett–Teller (BET) surface-area analyzers. The Rh/MgSNTs(a2) catalyst shows excellent catalytic activity, selectivity and superior cyclicity. The catalyst could be easily recovered by phase separation and was used up to four times.

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.

Direct Synthesis of Polysubstituted Aldehydes via Visible-Light Catalysis

Aldehydes are among the most versatile functional groups for synthetic chemistry. However, access to polysubstituted alkyl aldehydes is very limited and requires lengthy synthetic routes that involve multiple-step functional-group conversion. This paper reports a one-step synthesis of polysubstituted aldehydes from readily available olefin substrates using visible-light photoredox catalysis. Despite a number of competing reaction pathways, commercial styrenes react with vinyl ethers selectively in the presence of an acridinium salt photooxidant and a disulfide hydrogen-atom-transfer catalyst under blue LED irradiation. Alkyl aldehydes with different substitution patterns are prepared in good yields. This strategy can be applied to structurally sophisticated substrates.

Featuring Xantphos

This review highlights the use of the bisphosphine ligand group in homogeneous catalysis.

Accessing and predicting the kinetic profiles of homogeneous catalysts from volcano plots

Volcano plots, which generally describe only thermodynamics, are expanded to include kinetics that markedly influence the performance of homogeneous catalysts.

Volcano plots are frequently used as aids in the search for new heterogeneous and electrochemical catalysts. These tools successfully predict catalytic processes based solely on thermodynamic descriptions, which also capably describe many aspects of the catalytic cycles of homogeneous species. However, homogeneous catalysts also frequently depend upon the kinetic influences brought about by steric interactions to promote or prevent specific chemical reactions. Here, a prototypical transformation facilitated by a homogeneous catalysis, the hydroformylation of an olefin using CO and H₂, is examined to establish the viability of creating kinetic volcano plots and to determine their ability to ascertain the influences steric bulk plays on catalytic cycle energetics. Similar to their thermodynamic counterparts, kinetic volcanoes successfully reproduce many experimentally known facets of the hydroformylation reaction. In contrast to thermodynamic volcanoes, kinetic volcanoes emphasize changes in the height of the different activation barriers brought about by steric interactions. This crucial information, however, comes with considerable computational cost, since the transition states of catalysts bearing large bulky ligands must be identified and characterized. To overcome this drawback, a procedure is proposed that relates a simple steric parameter, the Tolman cone angle, with the descriptors used to create the kinetic volcano plots. In this way, the activation barriers of bulky catalysts can be estimated without requiring expensive transition state computations. These newly derived structure–activity relationship volcano plots represent useful tools for identifying new homogeneous catalysts.

Magnetic nanoparticle-supported ferrocenylphosphine: a reusable catalyst for hydroformylation of alkene and Mizoroki–Heck olefination

This study was focused on regioselective, re-usable and solvent-free catalysis using Fe3O4@dop-BPPF nanomaterials.

First efficient catalyst recycling for the iridium-catalysed hydroformylation of 1-octene

This paper describes the development of an efficient catalyst recycling concept for the iridium-catalysed hydroformylation of 1-octene through the investigation of biphasic systems, thermomorphic solvent systems and an ex situ extraction.

Ruthenium-catalyzed hydroformylation: from laboratory to continuous miniplant scale

Ruthenium running its rounds – recycling of a homogeneous ruthenium catalyst for hydroformylation of linear aliphatic alkenes by ex situ product extraction and successful application in a continuously operated miniplant for 90 h.

Computational aspects of hydroformylation

This review is to focus on computational studies on hydroformylation and theoretical coordination chemistry results related to hydroformylation.

Sequential hydroformylation/diels-alder processes: one-pot synthesis of polysubstituted cyclohexenes, cyclohexadienes, and phthalates from alkynes

A novel, one-pot hydroformylation/Diels-Alder sequence for the synthesis of multisubstituted cyclohexenes, cyclohexadienes, and phthalates has been developed. Various alkynes were efficiently converted into the corresponding products in good yields and with excellent diastereoselectivity through palladium-catalyzed hydroformylation followed by an AAD-type reaction (AAD: Amides-Aldehydes-Dienophiles). In view of the availability of the substrates, the atom-efficiency of the overall process, and the convenient introduction of substituents in the cyclohexene ring, this method complements current methods for the preparation of polysubstituted cyclohexane derivatives.

Transition-metal-catalyzed carbonylation reactions of olefins and alkynes: a personal account

Carbon monoxide was discovered and identified in the 18th century. Since the first applications in industry 80 years ago, academic and industrial laboratories have broadly explored CO's use in chemical reactions. Today organic chemists routinely employ CO in organic chemistry to synthesize all kinds of carbonyl compounds. Despite all these achievements and a century of carbonylation catalysis, many important research questions and challenges remain. Notably, apart from academic developments, industry applies carbonylation reactions with CO on bulk scale. In fact, today the largest applications of homogeneous catalysis (regarding scale) are carbonylation reactions, especially hydroformylations. In addition, the vast majority of acetic acid is produced via carbonylation of methanol (Monsanto or Cativa process). The carbonylation of olefins/alkynes with nucleophiles, such as alcohols and amines, represent another important type of such reactions. In this Account, we discuss our work on various carbonylations of unsaturated compounds and related reactions. Rhodium-catalyzed isomerization and hydroformylation reactions of internal olefins provide straightforward access to higher value aldehydes. Catalytic hydroaminomethylations offer an ideal way to synthesize substituted amines and even heterocycles directly. More recently, our group has also developed so-called alternative metal catalysts based on iridium, ruthenium, and iron. What about the future of carbonylation reactions? CO is already one of the most versatile C1 building blocks for organic synthesis and is widely used in industry. However, because of CO's high toxicity and gaseous nature, organic chemists are often reluctant to apply carbonylations more frequently. In addition, new regulations have recently made the transportation of carbon monoxide more difficult. Hence, researchers will need to develop and more frequently use practical and benign CO-generating reagents. Apart from formates, alcohols, and metal carbonyls, carbon dioxide also offers interesting options. Industrial chemists seek easy to prepare catalysts and patent-free ligands/complexes. In addition, non-noble metal complexes will interest both academic and industrial researchers. The novel Lucite process for methyl methacrylate is an important example of an improved catalyst. This reaction makes use of a specific palladium/bisphosphine catalyst, which led to the successful implementation of the technology. More active and productive catalysts for related carbonylations of less reactive olefins would allow for other large scale applications of this methodology. From an academic point of view, researchers continue to look for selective reactions with more functionalized olefins. Finally, because of the volatility of simple metal carbonyl complexes, carbonylation reactions today remain a domain of homogeneous catalysis. The invention of more stable and recyclable heterogeneous catalysts or metal-free carbonylations (radical carbonylations) will be difficult, but could offer interesting challenges for young chemists.