Ligands In Hydroformylation Research Articles

Modular Synthesis of Phosphite and Phosphoramidite Ligands for Rh‐Catalyzed Hydroformylation

AbstractRhodium‐catalyzed hydroformylation of olefins is an important method for synthesizing aldehydes, and it is worth noting that regioselectivity and enantioselectivity of the product controlled by ligand are the most commonly used strategies. The modular synthesis of phosphite and phosphoramidite ligands have significant advantages of simple synthesis and high catalytic activity, which was why these ligands have been widely used in hydroformylation reactions. Herein, we focus on the synthesis methods and design ideas of such ligands, as well as their application effects in hydroformylation reactions. This review aims to provide a reference for the design and synthesis of ligands in hydroformylation subsequently.

Phosphorus Ligands in Hydroformylation and Hydrogenation: A Personal Account.

Metal-catalyzed hydroformylation and hydrogenation heavily rely on ligands, among which phosphorous ligands play a pivotal role. This personal account presents a selection of three distinct classes of phosphorous ligands, namely, monodentate meta-substituted phosphinites, bis-phosphites, and P-chiral supramolecular phosphines, developed in our group. The synthesis of these ligands, isolation, characterization, and their performance in transition metal-catalyzed hydroformylation, isomerizing hydroformylation, and asymmetric hydrogenation of olefins is summarized. The state of the art development in iron-catalyzed hydroformylation of alkenes and our contributions to the field is discussed. Use of phosphines enabled iron-catalyzed hydroformylation of alkenes under mild conditions. Thus, this account demonstrates the central role of phosphorus ligands in industrially relevant transformations such as hydrogenation and hydroformylation. The seemingly matured field of ligand discovery still holds significant potential and will steer the field of homogeneous catalysis.

Boosting the hydrolytic stability of phosphite ligand in hydroformylation by the construction of superhydrophobic porous framework

The development of a catalyst that delivers high activities and selectivities with excellent durability is of great importance. Numerous efficient catalysts suffer from the inherent hydrolysis liabilities, plaguing their practical applications. Herein, we show that this challenge can be tackled by constructing them into superhydrophobic porous frameworks, as exemplified by a water-sensitive phosphite ligand, tris(2-tert-butylphenyl) phosphite. The efficiency and long-term stability of the developed system are remarkably high in the hydroformylation of internal olefins after metalation with Rh species, superior to the corresponding homogeneous analogues. The significantly boosted hydrolytic stability allows for catalytic transformations using water as a green solvent, which not only facilitates the isolation of the products, but also furnishes the aldehydes with higher regioselectivities for the desired linear form in comparison with that operated under benchmark conditions using toluene as a reaction medium. Given these promising results, we anticipate the strategy advanced herein will form the basis for constructive perspectives in the enhancement of the water resistance of catalysts and the development of high performance hydroformylation catalysts.

Backbone-Modified Bisdiazaphospholanes for Regioselective Rhodium-Catalyzed Hydroformylation of Alkenes

A series of tetraaryl bisdiazaphospholane (BDP) ligands were prepared varying the phosphine bridge, backbone, and substituents in the 2- and 5-positions of the diazaphospholane ring. The parent acylhydrazine backbone was transformed to an alkylhydrazine via a borane reduction procedure. These reduced ligands contained an all sp3 hybridized ring mimicking the all sp3 phospholane of (R,R)-Ph-BPE, a highly selective ligand in asymmetric hydroformylation. The reduced bisdiazaphospholane (red-BDP) ligands were shown crystallographically to have an increased C–N–N–C torsion angle—this puckering resembles the structure of (R,R)-Ph-BPE and has a dramatic influence on regioselectivity in rhodium catalyzed hydroformylation. The red-BDPs demonstrated up to a 5-fold increase in selectivity for the branched aldehyde compared to the acylhydrazine parent ligands. This work demonstrates a facile procedure for increased branched selectivity from the highly active and accessible class of BDP ligands in hydroformylation.

Pyrazoles as ligands for the Rh-catalyzed hydroformylation of alkenes in supercritical carbon dioxide

Activity of pyrazole ligands in hydroformylation of a number of unsaturated terminal substrates in supercritical carbon dioxide (scCO2) in the presence of Rh-catalyst was studied. The ligands without free NH group at position 1 of the pyrazole ring were found to be active. The use of scCO2 as the reaction medium served to reach a higher conversion and regioselectivity of hydroformylation as compared to those in toluene.

The electron-poor phosphines P{C6H3(CF3)2-3,5}3 and P(C6F5)3 do not mimic phosphites as ligands for hydroformylation. A comparison of the coordination chemistry of P{C6H3(CF3)2-3,5}3 and P(C6F5)3 and the unexpectedly low hydroformylation activity of their rhodium complexes

The fluoroaryl phosphines P{C6H3(CF3)2-3,5}3 (La) and P(C6F5)3 (Lb) form the complexes trans-[MCl2(La)2] and trans-[MCl2(Lb)2](M = Pd or Pt) which have been isolated and fully characterised. 31P NMR studies of competition experiments show that the stability of trans-[PdCl2L2] is in the order L = Lb< La <PPh3. The crystal structure of trans-[PtCl2(La)2] is reported and reveals that the Pt-P bond lengths in trans-[PtCl2L2] are in the order L = Lb< La < PPh3. The equilibria established when [Pt(norbornene)3] is treated with or are investigated by 31P and 195Pt NMR spectroscopy and the species [PtLn(norbornene)3-n](n= 1-3) identified. Ligands and appear to have similar affinities for platinum(0). The complexes trans-[MCl(CO)(La)2] and trans-[MCl(CO)(Lb)2](M = Rh or Ir) have been synthesised and fully characterised; the values of nu(CO) are comparable with those for analogous phosphite complexes. The ligands La, Lb, P(C6H2F3-3,4,5)3 (Lc), P{C6H4(CF3)-2}3 (Ld), PPh3 and P(OPh)3 have been tested in rhodium-catalysed hydroformylation of 1-hexene and La, Lb, and PPh3 have been tested in rhodium-catalysed hydroformylation of 4-methoxystyrene. Ligands La, and Lb, have been shown to be stable under the hydroformylation catalysis conditions. For the 1-hexene reaction, the activity and selectivity for and are very similar to the PPh3 catalyst (TOF ca. 400 h(-1); n : iso 2.5-3.0) but for the sterically demanding and the activity and selectivity was much lower than with PPh3 (TOF ca. 15, n : iso ratio 0.6). Thus, the yield of heptanals obtained with the catalyst derived from La is 94% while under the same conditions with Lb only 6%. The TOF for the La/Rh catalyst was 5 times lower than for the P(OPh)3/Rh catalyst despite the superficially similar ligand electronic characteristics for La and P(OPh)3.

Phenoxaphosphino‐Modified Xantphos‐Type Ligands in the Rhodium‐Catalysed Hydroformylation of Internal and Terminal Alkenes

AbstractThe solubility of the modifying ligand is an important parameter for the efficiency of a rhodium‐catalysed hydroformylation system. A facile synthetic procedure for the preparation of well‐defined xanthene‐type ligands was developed in order to study the influence of alkyl substituents at the 2‐, and 7‐positions of the 9,9‐dimethylxanthene backbone and at the 2‐, and 8‐positions of the phenoxaphosphino moiety of ligands 1–16 on solubility in toluene and the influence of these substituents on the performance of the ligands in the rhodium‐catalysed hydroformylation. An increase in solubility from 2.3 mmol⋅L−1 to &gt;495 mmol⋅L−1 was observed from the least soluble to the most soluble ligand. A solubility of at least 58 mmol⋅L−1 was estimated to be sufficient for a large‐scale application of these ligands in hydroformylation. Highly active and selective catalysts for the rhodium‐catalysed hydroformylation of 1‐octene and trans‐2‐octene to nonanal, and for the hydroformylation of 2‐pentene to hexanal were obtained by employing these ligands. Average rates of &gt;1600 (mol aldehyde) × (mol Rh)−1×h−1 {conditions: p(CO/H2) = 20 bar, T = 353 K, [Rh] = 1 mM, [alkene] = 637 mM} and excellent regio‐selectivities of up to 99% toward the linear product were obtained when 1‐octene was used as substrate. For internal olefins average rates of &gt;145 (mol aldehyde)×(mol Rh)−1×h−1 {p(CO/H2) = 3.6–10 bar, T = 393 K, [Rh] = 1 mM, [alkene] = 640–928 mM} and high regio‐selectivities up to 91% toward the linear product were obtained.

ChemInform Abstract: Phosphorus‐Chiral Diphosphines as Ligands in Hydroformylation. An Investigation on the Influence of Electronic Effects in Catalysis.

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Hydroformylation of 1-hexene and propene with in situ formed rhodium phosphine catalysts

A series of triphenylphosphines modified with different heteroatom groups (SCH 3, N(CH 3) 2, OCH 3, CF 3) in ortho or para position of the phenyl ring(s) were synthesised and tested for their catalytic behaviour in the rhodium catalysed hydroformylation of 1-hexene (80°C, 15 bar) and propene (100°C, 10 bar). Hydroformylation results for 1-hexene and propene differed markedly. With 1-hexene, the differences in activity and in chemo- and regioselectivity obtained with the various ligands were minor. Among the heterodonor ligands, the strong σ-donor ligands yielded higher hydroformylation activity than the less basic ligands. In the case of propene, heterodonor bidentate ligands suppressed the hydroformylation reaction. In addition, 1,4-bis(diphenylphosphino)butane and ( o-thiomethylphenyl)bis(1-naphthyl)phosphine favoured the formation of n-butanal. Only the CF 3 modified ligands behaved similarly with the two alkenes. The influence of the structure of the ligand in hydroformylation was studied by using molecular modelling methods. The steric size of the ab initio energy minimised free ligand structures was evaluated by Tolman’s cone angle method. Co-ordination properties of CF 3 group modified phosphines were studied in reaction with Rh 2(CO) 4Cl 2, and the structure of Rh(CO)Cl(P( o-CF 3C 6H 4)Ph 2) 2 ( 1) was determined crystallographically.

Phosphorus-Chiral Diphosphines as Ligands in Hydroformylation. An Investigation on the Influence of Electronic Effects in Catalysis

The phosphorus-chiral diphosphine 1,1‘-bis(1-naphthylphenylphosphino)ferrocene (1a) and its new electronically modified derivatives 1b−d bearing methoxy and/or trifluoromethyl groups in para positions of the phenyl rings were investigated as ligands in rhodium-catalyzed (asymmetric) hydroformylation. Depending on ligand basicity, high-pressure NMR and IR characterization of the respective (diphosphine) rhodium dicarbonyl hydride precursor complexes revealed subtle differences in the occupation of bis-equatorial (ee) and equatorial−apical (ea) coordination geometries. The high ee:ea ratio of the four complexes contrasted with the clear ea preference observed for the related achiral compound dppf (1,1‘-bis(diphenylphosphino)ferrocene). In the hydroformylation of styrene the best result (50% ee) was obtained by employing the best π-acceptor ligand 1c, incorporating two p-trifluoromethyl substituents. Substrate electronic variations using 4-methoxystyrene and 4-chlorostyrene showed a pronounced influence on t...

ChemInform Abstract: FURTHER STUDIES ON THE HOMOGENEOUS HYDROFORMYLATION OF ALKENES BY USE OF RUTHENIUM COMPLEX CATALYSTS

AbstractDie Hydroformylierung von Alkenen [ z.IB.

Further studies on the homogeneous hydroformylation of alkenes by use of ruthenium complex catalysts

The use of several tertiary-phosphine–ruthenium complexes in the catalytic hydroformylation of alkenes is described. For mononuclear complexes the conversions into aldehyde, as well as the ratios of straight- to branched-chain aldehyde are essentially constant; the ruthenium complex recovered from the reactions is invariably tricarbonylbis(triphenylphosphine) ruthenium(0), Ru(CO)3(PPh3)2. The dependence of conversion and aldehyde ratios on catalyst concentration, temperature, partial and total pressures, nature of the substrate, and addition of excess of triphenylphosphine and other ligands in hydroformylation with Ru(CO)3(PPh3)2 is also described. Based on these results, a mechanism involving Ru(H)2(CO)2(PPh3) as the principal active catalytic species is suggested.The compound Ru(CO)3(PPh3)2 is also active for the hydrogenation of alkenes and aldehydes and mechanisms for these reactions are suggested.Complexes formed by addition of various ligands to dodecacarbonyltriruthenium, Ru3(CO)12, are shown to be less active for hydroformylation than mononuclear complexes.