Hydroformylation of alkenes: An industrial view of the status and importance

Robust, scalable, and highly selective spirocyclic catalysts for industrial hydroformylation and isomerization-hydroformylation

Hydroformylation (HF) or isomerization-hydroformylation (ISO-HF) represents the most direct and practical route for producing aldehydes on an industrial scale. To resolve the issues of low activity, low linear/branched (l/b) ratio, and low stability in HF and ISO-HF, we herein reported a class of spirocyclic diphosphites. Notably, the ligand termed O-SDPhite afforded excellent catalytic activity and regioselectivity for the HF of various olefins. Excellent l/b ratio and an unprecedented turnover number of up to 17,620,000 were achieved. O-SDPhite was also found to be effective in the regioselective ISO-HF of the industrially related cheap and abundant C4 Raffinates to n-valeraldehyde produced on a multimillion-ton scale. The reaction with O-SDPhite, superior to that of benchmark Biphephos, was continuously operated for 41 days and afforded an average 38.6 l/b ratio (31 days and 14.7 l/b ratio for Biphephos).

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.

CuH-Catalyzed Regio- and Enantioselective Formal Hydroformylation of Vinyl Arenes

A highly enantioselective formal hydroformylation of vinyl arenes enabled by copper hydride (CuH) catalysis is reported. Key to the success of the method was the use of the mild Lewis acid zinc triflate to promote the formation of oxocarbenium electrophiles through the activation of diethoxymethyl acetate. Using the newly developed protocol, a broad range of vinyl arene substrates underwent efficient hydroacetalization reactions to provide access to highly enantioenriched α-aryl acetal products in good yields with exclusively branched regioselectivity. The acetal products could be converted to the corresponding aldehydes, alcohols, and amines with full preservation of the enantiomeric purity. Density functional theory studies support that the key C-C bond-forming event between the alkyl copper intermediate and the oxocarbenium electrophile takes place with inversion of configuration of the Cu-C bond in a backside SE2-type mechanism.

Developments in the Catalytic Asymmetric Synthesis of Agrochemicals and Their Synthetic Importance

Catalytic asymmetric synthesis has become an essential tool for the enantioselective synthesis of pharmaceuticals, natural products, and agrochemicals (mainly fungicides, herbicides, insecticides, and pheromones). With continuous growing interest in both modern agricultural chemistry and catalytic asymmetric synthesis chemistry, this review provides a comprehensive overview of some earlier reports as well as the recent successful applications of various catalytic asymmetric syntheses methodologies, such as enantioselective hydroformylation, enantioselective hydrogenation, asymmetric Sharpless epoxidation and dihydroxylation, asymmetric cyclopropanation or isomerization, organocatalyzed asymmetric synthesis, and so forth, which have been used as key steps in the preparation of chiral agrochemicals (on R&D, piloting, and commercial scales). Chiral agrochemicals can also lead the new generation of such chemicals having specific and novel modes of action for achieving sustainable crop protection and production. Some perspectives and challenges for these catalytic asymmetric methodologies in the synthesis of chiral agrochemicals are also briefly discussed in the final section of the manuscript. This review will provide the insight regarding understanding, development, and evaluation of catalytic asymmetric systems for the synthesis of chiral agrochemicals among the agrochemists.

Effectively Regulating the Microenvironment of Atomically Dispersed Rh through Co and Pi to Promote the Selectivity in Olefin Hydroformylation

In the study of heterogeneity of homogeneous processes, effective control of the microenvironment of active sites is a reliable means to improve the selectivity of products. Here, we develop a high-performance Rh-based atomically dispersed catalyst for olefin hydroformylation by controlling the electronic environment and spatial distribution of active metals on the supports, which is achieved through wet impregnation of Rh on ZnO modified with Pi and Co. Various characterizations demonstrate that Co weakens Rh-CO interactions and Pi promotes the formation of atomically dispersed Rh, which thereby improves the selectivity of linear aldehydes in hydroformylation. This strategy of rationally designing the local microenvironment of active metals is important to optimize the catalytic performance.

Synthesis of Nixantphos Core-Functionalized Amphiphilic Nanoreactors and Application to Rhodium-Catalyzed Aqueous Biphasic 1-Octene Hydroformylation

A latex of amphiphilic star polymer particles, functionalized in the hydrophobic core with nixantphos and containing P(MAA-co-PEOMA) linear chains in the hydrophilic shell (nixantphos-functionalized core-crosslinked micelles, or nixantphos@CCM), has been prepared in a one-pot three-step convergent synthesis using reversible addition-fragmentation chain transfer (RAFT) polymerization in water. The synthesis involves polymerization-induced self-assembly (PISA) in the second step and chain crosslinking with di(ethylene glycol) dimethacrylate (DEGDMA) in the final step. The core consists of a functionalized polystyrene, obtained by incorporation of a new nixantphos-functionalized styrene monomer (nixantphos-styrene), which is limited to 1 mol%. The nixantphos-styrene monomer was synthesized in one step by nucleophilic substitution of the chloride of 4-chloromethylstyrene by deprotonated nixantphos in DMF at 60 °C, without interference of either phosphine attack or self-induced styrene polymerization. The polymer particles, after loading with the [Rh(acac)(CO)₂] precatalyst to yield Rh-nixantphos@CCM, function as catalytic nanoreactors under aqueous biphasic conditions for the hydroformylation of 1-octene to yield n-nonanal selectively, with no significant amounts of the branched product 2-methyl-octanal.

Effects of Substitution Pattern in Phosphite Ligands Used in Rhodium-Catalyzed Hydroformylation on Reactivity and Hydrolysis Stability

The stability of homogeneous catalytic systems is an industrially crucial topic, which, however, receives comparatively little attention from academic research. Phosphites are among the most frequently used ligands in industrial, rhodium-catalyzed n-regioselective hydroformylation. However, they are particularly vulnerable to hydrolysis. Since the decomposition of ligands should be dependent on the substitution patterns, phenyl, tert-butyl and condensed ring systems of benzopinacolphosphites were evaluated concerning their activity, regioselectivity and hydrolysis stability. A series of twelve strongly related phosphites were synthesized, tested in the hydroformylation of isomeric n-octenes, and studied in hydrolysis experiments using in situ NMR spectroscopy. Our results show that substituents in the ortho-position, especially tert-butyl substituents, enhance hydrolysis stability while maintaining compelling activity and regioselectivity. In contrast, substituents in the para-position may destabilize the phosphite.

Enantioselective Synthesis of 4-Methyl-3,4-dihydroisocoumarin via Asymmetric Hydroformylation of Styrene Derivatives

Enantioenriched aldehydes are produced through asymmetric hydroformylation of styrene derivatives using BIBOP-type ligands. The featured example is enantioselective synthesis of 4-methyl-3,4-dihydroisocoumarin, which was prepared in a 95.1:4.9 enantiomeric ratio from asymmetric hydroformylation of ethyl 2-vinylbenzoate followed by in situ lactonization during the reduction process. The conditions are compatible with both electron-rich and electron-poor substituents.

Recent Developments in the Scope, Practicality, and Mechanistic Understanding of Enantioselective Hydroformylation

In the nearly 80 years since catalytic hydroformylation was first reported, hundreds of billions of pounds of aldehyde have been produced by this atom efficient one-carbon homologation of alkenes in the presence of H₂ and CO. Despite the economy and demonstrated scalability of hydroformylation, the enantioselective process (asymmetric hydroformylation, AHF) currently does not contribute significantly to the production of chiral aldehydes and their derivatives. Current impediments to practical application of AHF include low diversity of chiral ligands that provide effective rates and selectivities, limited exploration of substrate scope, few demonstrations of efficient flow reactor processes, and incomplete mechanistic understanding of the factors that control reaction selectivity and rate. This Account summarizes developments in ligand design, substrate scope, reactor technology, and mechanistic understanding that advance AHF toward practical and atom-efficient production of chiral α-stereogenic aldehydes. Initial applications of AHF were limited to activated terminal alkenes such as styrene, but recent developments enable high selectivity for unactivated olefins and more complex substrates such as 1,1'- and 1,2-disubstituted alkenes. Expanded substrate scope primarily results from new chiral phosphine ligands, especially phospholanes and bisdiazaphospholanes (BDPs). These ligands are now more accessible due to improved synthesis and resolution procedures. One of the virtues of diazaphospholanes is the relative ease of derivatization, including attachment to heterogeneous supports. Hydroformylation involves toxic and flammable reactants, a serious concern in pharmaceutical production facilities. Flow reactors offer many process benefits for handling dangerous reagents and for systematically moving from research to production scales. New approaches to achieving good gas-liquid mixing in flow reactors have been demonstrated with BDP-derived catalyst systems and lend assurance that AHF can be practically implemented by the pharmaceutical and fine chemical industries. To date, progress in AHF has been empirically driven, because hydroformylation is a complex, multistep process for which the origins of chemo-, regio-, and enantioselectivity are difficult to elucidate. Mechanistic complexity arises from three concurrent catalytic cycles (linear and two diastereomeric branched paths), significant pooling of catalyst as off-cycle species, and multiple elementary steps that are kinetically competitive. Addressing such complexity requires new approaches to collecting kinetic and extra-kinetic information and analyzing these data. In this Account, we describe our group's progress toward understanding the complex kinetics and mechanism of AHF as catalyzed by rhodium bis(diazaphospholane) catalysts. Our strategy features both "outside-in" (i.e., monitoring catalytic rates and selectivities as a function of reactant concentration and temperature) and "inside-out" (i.e., building kinetic models based on the rates of component steps of the catalytic reaction) approaches. These studies include isotopic labeling, interception and characterization of catalytic intermediates using NMR techniques, multinuclear high-pressure NMR spectroscopy, and sophisticated kinetic modeling. Such broad-based approaches illuminate the kinetic and mechanistic origins of selectivity and activity of AHF and the elucidation of important principles that apply to all catalytic reactions.

Mn-, Fe-, and Co-Catalyzed Radical Hydrofunctionalizations of Olefins

Cofactor-mimetic aerobic oxidation has conceptually merged with catalysis of syngas reactions to form a wide range of Markovnikov-selective olefin radical hydrofunctionalizations. We cover the development of the field and review contributions to reaction invention, mechanism, and application to complex molecule synthesis. We also provide a mechanistic framework for understanding this compendium of radical reactions.

Synthesis and application of a new triphosphorus ligand for regioselective linear hydroformylation: a potential way for the stepwise replacement of PPh3 for industrial use

A new triphosphorus ligand, Tribi, for regioselective linear hydroformylation of terminal and internal olefins with excellent catalytic activity and regioselectivity.

Synthesis of (-)-Indolizidine 167B based on domino hydroformylation/cyclization reactions

The synthesis of (-)-Indolizidine 167B has been achieved from optically active (R)-3-(pyrrol-1-yl)hex-1-ene. The key step is a highly regioselective hydroformylation reaction and a one-pot intramolecular cyclization providing a general approach to the indolizine nucleus.