Dual Rh-Ru Catalysts for Reductive Hydroformylation of Olefins to Alcohols

Pd-Catalyzed Regioselective Hydroxymethylation of Olefins with HCO2H via Sequential Hydroformylation and Reduction

An effective Pd-catalyzed regioselective hydroxymethylation of olefins with HCO2H and Ac2O is described. A variety of primary alcohols can be obtained in up to 94% yield and a >20:1 l:b ratio via sequential hydroformylation and reduction. The reaction is operationally simple with no need for external CO and H2.

Methanolation of Olefins: Low-Pressure Synthesis of Alcohols by the Formal Addition of Methanol to Olefins

Methanolation of olefins is introduced as a new low-pressure synthetic pathway to C1 elongated alcohols. Formally, H3COH is added to the C=C bond in a 100 % atom efficient manner. Mechanistically, the overall transformation occurs as a tandem reaction sequence by combining the dehydrogenation of methanol to syngas at a CO : H2 ratio of 1 : 2 with subsequent hydroformylation to the corresponding aldehyde and its final hydrogenation to the alcohol. The dehydrogenation and hydrogenation steps are catalyzed by a Mn/pincer complex, while the hydroformylation is accomplished by a Rh/phosphine catalyst. Using 1-octene as prototypical substrate, a yield of 80 % nonanol was achieved with a ratio of 93 : 7 of linear to branched alcohols and turnover numbers (TONRh) of more than 17 000 could be obtained in relation to the precious metal Rhodium. The integrated catalytic system provides direct access to alcohols from olefins and "green" methanol, avoiding the handling of pressurized CO and H2 and the use of specialized high-pressure equipment as the process conditions do not exceed 10 bar with partial pressures of syngas in the range of only 1-2 bar.

Rhodium/Trialkylamines Catalyzed Reductive Hydroformylation in Ionic Liquid/Heptane Medium: An Unexpected Concept for Catalyst Recycling in Batch and Continuous Flow Processes

We report here the rhodium catalyzed reductive hydroformylation of methyl 10-undecenoate. Our approach is based on an ionic liquid/heptane biphasic system associated with commercially available trialkylamines. The effects of various reaction parameters such as amine type, amine amount, temperature, syngas pressure and composition were studied in order to minimize the rhodium leaching and increase the production of primary alcohols. Although the amine is less soluble in the ionic liquid than in heptane, the catalytic system is efficiently maintained in the ionic liquid phase. For the optimized conditions, the catalytic ionic liquid layer can be recycled at least nine times by keeping an alcohol yield over 50 % and by limiting the rhodium leaching. As an extension of this system and to examine the long-term stability, this batch system was transferred to a miniplant for a continuous flow process. A pilot plant was operated for 45 h of total reaction time, reaching a TTON of 232 for alcohol production.

Selective Hydrogenation of Aldehydes under Syngas Using CeO2-Supported Au Nanoparticle Catalyst

Chemoselective hydrogenation of aldehydes to alcohols is of importance in synthetic chemistry. Here, we report a reusable CeO2-supported Au nanoparticle catalyst for the selective hydrogenation of aldehydes using syngas as the hydrogen source for which CO in syngas works as a site blocker to prevent side reactions. In particular, the hydrogenation of aldehydes with an easily reducible alkene, alkyne, or halogen moiety under syngas gave the corresponding alcohols with high selectivity, while the hydrogenation under pure hydrogen resulted in overreduction or dehalogenation. Of particular interest is that CO works as a site blocker but does not affect the hydrogenation rate significantly. A potential application of the present catalyst system was demonstrated by the conversion of terminal alkenes to alcohols via a one-pot hydroformylation/hydrogenation sequence.

Alcohol Synthesis by Cobalt-Catalyzed Visible-Light-Driven Reductive Hydroformylation

A cobalt-catalyzed reductive hydroformylation of terminal and 1,1-disubstituted alkenes is described. One-carbon homologated alcohols were synthesized directly from CO and H₂, affording anti-Markovnikov products (34-87% yield) with exclusive regiocontrol (linear/branch >99:1) for minimally functionalized alkenes. Irradiation of the air-stable cobalt hydride, (dcype)Co(CO)₂H (dcype = dicyclohexylphosphinoethane) with blue light generated the active catalyst that mediates alkene hydroformylation and subsequent aldehyde hydrogenation. Mechanistic origins of absolute regiocontrol were investigated by in situ monitoring of the tandem catalytic reaction using multinuclear NMR spectroscopy with syngas mixtures.

Isoselective Hydroformylation of Propylene by Iodide-Assisted Palladium Catalysis

Isobutanal is a high value bulk material that, in principle, could be produced with 100 % atom-economy by isoselective hydroformylation of propylene with syngas. However, leading industrial Rh- and Co-catalyzed hydroformylation methods preferentially form n-butanal over the iso-product, and methods offering isoselectivity remain underdeveloped. Here we report an iodide-assisted Pd-catalyzed hydroformylation of propylene that produces isobutanal with unprecedented levels of selectivity. The method involves PdI2 , simple alkyl monophosphines, such as tricyclohexylphosphine, and common green solvents, enabling the title reaction to occur with isoselectivity in up to 50 : 1 iso/n product ratios under industrially relevant conditions (80-120 °C). The catalytic and preliminary mechanistic experiments indicate a key role of the iodide anions in both the catalytic activity and the isoselectivity.

Auto-Tandem Catalytic Reductive Hydroformylation in a CO2-Switchable Solvent System

Upgradation of olefin-enriched Fischer-Tropsch cuts by the synthesis of alcohols leads to drop-in-capable biosynthetic fuels with low carbon emissions. As an alternative to the conventional two-step production of long-chain alcohols, tandem catalytic systems improve the energy and resource efficiency. Herein, we present an auto-tandem catalytic system for the production of alcohols from olefin-paraffin mixtures. By utilization of a tertiary alkanolamine as the ligand as well as the switchable component in the solvent system, a lean reaction system capable of catalyst recycling was developed. The system was characterized with regard to the switchable solvent separation approach and reaction parameters, resulting in alcohol yields of up to 99.5% and turnover frequencies of up to 764 h^-1. By recycling the catalyst in 10 consecutive reactions, a total turnover number of 2810 was achieved.

Auto-tandem catalytic reductive hydroformylation with continuous multiphase catalyst recycling

This work covers auto-tandem catalytic hydroformylation and hydrogenation for the synthesis of alcohols for synthetic fuels from renewable olefin cuts. A multiphase catalyst recycling system was proven to be feasible in continuous flow.

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.

Reductive Hydroformylation of Isosorbide Diallyl Ether

Isosorbide and its functionalized derivatives have numerous applications as bio-sourced building blocks. In this context, the synthesis of diols from isosorbide diallyl ether by hydrohydroxymethylation reaction is of extreme interest. This hydrohydroxymethylation, which consists of carbon-carbon double bonds converting into primary alcohol functions, can be obtained by a hydroformylation reaction followed by a hydrogenation reaction. In this study, reductive hydroformylation was achieved using isosorbide diallyl ether as a substrate in a rhodium/amine catalytic system. The highest yield in bis-primary alcohols obtained was equal to 79%.

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.

Ruthenium-catalysed domino hydroformylation–hydrogenation–esterification of olefins

Aliphatic esters are made easily from acetic acid, olefins, and synthesis gas. In the presence of ruthenium–phosphine complexes novel domino-hydroformylation–hydrogenation–esterification proceeds in moderate to good yields.

Transition metal-catalyzed alkene isomerization as an enabling technology in tandem, sequential and domino processes

One-pot reactions based on catalytic isomerization of alkenes not only offer the inherent advantages of atom-, step- and redox-economy but also enable the preparation of value-added products that would be difficult to access by conventional methods.

n-Alkanes to n-alcohols: Formal primary C─H bond hydroxymethylation via quadruple relay catalysis

Nature is able to synergistically combine multiple enzymes to conduct well-ordered biosynthetic transformations. Mimicking nature's multicatalysis in vitro may give rise to new chemical transformations via interplay of numerous molecular catalysts in one pot. The direct and selective conversion of abundant n-alkanes to valuable n-alcohols is a reaction with enormous potential applicability but has remained an unreached goal. Here, we show that a quadruple relay catalysis system involving three discrete transition metal catalysts enables selective synthesis of n-alcohols via n-alkane primary C─H bond hydroxymethylation. This one-pot multicatalysis system is composed of Ir-catalyzed alkane dehydrogenation, Rh-catalyzed olefin isomerization and hydroformylation, and Ru-catalyzed aldehyde hydrogenation. This system is further applied to synthesis of α,ω-diols from simple α-olefins through terminal-selective hydroxymethylation of silyl alkanes.

Green hydroboration of carboxylic acids and mechanism investigation

A catalyst-free and solvent-free method for the hydroboration of a variety of carboxylic acids with pinacolborane was developed. The hydroboration of various aromatic and aliphatic carboxylic acids as well as dicarboxylic acids with HBpin could be completed within 6 h at room temperature or within 1 h at 60 °C to give the products in quantitative yields under neat conditions without the need for any solvent or metal catalyst. The possible reaction mechanism was investigated in detail based on the corresponding DFT calculations and the stoichiometric reaction of acetic acid with different equivalents of HBpin (at room temperature and 0 °C) and it revealed the stepwise nature of the protocol.