Bisphosphite Ligands Research Articles

Carbonyl-bis-{6,6'-[(3,3'-di-tert-butyl-5,5'-dimeth-oxy-1,1'-biphenyl-2,2'-di-yl)bis(oxy)]bis-(dibenzo[d,f][1,3,2]-dioxaphosphepine)}hydridorhodium(I) toluene-d 8 2.25-solvate.

The crystal-structure determination of the title compound, [RhH(C46H44O8P2)2(CO)]·2.25C7D8, is reported. The bis-phosphite ligand, C46H44O8P2, is well known as Biphephos. One specific characteristic of this hydrido rhodium(I) monocarbonyl complex is that one bis-phosphite ligand is coordinated in the expected bidentate mode and the other is coordinated in a monodentate mode. Thus, one phosphite moiety remains non-coordinating. All three coordinating phospho-rus atoms occupy the equatorial positions in the trigonal-bipyramidal environment around the rhodium atom. The crystals of the hydrido rhodium(I) monocarbonyl complex contains deuterated solvent mol-ecules (toluene-d 8). Most of them are included in the model, but the contributions of about 0.84 toluene per unit cell were removed from the diffraction data, using the SQUEEZE procedure in PLATON [Spek (2015 ▸). Acta Cryst. C71, 9-18].

Enantioselective Nickel‐Catalyzed Hydrosilylation of 1,1‐Disubstituted Allenes

AbstractHere, we report the first example of Ni‐catalyzed asymmetric hydrosilylation of 1,1‐disubstituted allenes with high level of regioselectivities and enantioselectivities. The key to achieve this stereoselective hydrosilylation reaction was the development of the SPSiOL‐derived bisphosphite ligands (SPSiPO). This protocol features broad substrate scope, excellent functional group, and heterocycle tolerance, thus provides a versatile method for the construction of enantioenriched tertiary allylsilanes in a straightforward and atom‐economic manner. DFT calculations were performed to reveal the reaction mechanism and the origins of the enantioselectivity.

Enantioselective Nickel-Catalyzed Hydrosilylation of 1,1-Disubstituted Allenes.

Here, we report the first example of Ni-catalyzed asymmetric hydrosilylation of 1,1-disubstituted allenes with high level of regioselectivities and enantioselectivities. The key to achieve this stereoselective hydrosilylation reaction was the development of the SPSiOL-derived bisphosphite ligands (SPSiPO). This protocol features broad substrate scope, excellent functional group, and heterocycle tolerance, thus provides a versatile method for the construction of enantioenriched tertiary allylsilanes in a straightforward and atom-economic manner. DFT calculations were performed to reveal the reaction mechanism and the origins of the enantioselectivity.

Synthesis, complexation behavior and catalytic performance of chelating bisphosphite ligands based on 9,10-brigded 9,10-dihydroanthracenes in Rh catalyzed hydroformylation of 4-pentenal

In the present work the modular synthesis of new chelating bisphosphite ligands based on 9,10-brigded 9,10-dihydroanthracenes as ligand backbones is presented. The complexation behavior of these ligands in rhodium metal complexes as well as mechanistic studies of the preformation step of the rhodium-catalysed hydroformylation is investigated. Ratio of coordination isomers in the Rh complexes of these ligands has been determined using NMR based calculation technique. Modular synthesis route was established allowing for a variety of ligands to be synthesized in a standard procedure The new ligands were tested in the hydroformylation of 4-pentenal under optimized conditions to give adipic aldehyde a promising starting material for the polyamide nylon-6,6. Ligand L3 showed the best selectivity towards adipic aldehyde with selectivity of 10.2/1 n/iso aldehyde.

Palladium-Based Supramolecularly Regulated Catalysts for Asymmetric Allylic Substitutions

Herein is reported the effect of different polyether binders (alkali metal, alkaline earth metal, and lanthanide salts) as regulation agents to enhance the catalytic properties of palladium complexes derived from enantiopure bisphosphite ligands in allylic substitutions. The addition of RbOAc or M(OTf)x (M = Mg2+, La3+, or Ho3+) led to positive effects in enantioselectivity (by up to 16% ee) for the allylic substitution reactions. These ligands coordinated in the usual cis-fashion or in an unprecedented trans-fashion to the palladium center, depending on the phosphite group, and presented different reactivity in the allylic substitutions.

Rhodium-Catalyzed Hydroformylation of 1,3-Butadiene to Adipic Aldehyde: Revealing Selectivity and Rate-Determining Steps

The reaction mechanism of Rh-catalyzed hydroformylation of 1,3-butadiene with triptycene-derived bisphosphite ligands L was studied by in situ NMR and IR experiments, kinetic measurements, and deuterioformylation. Under CO pressure the η3-crotyl complex (κ2-L)Rh(η3-crotyl)(CO) is a stable intermediate that slowly liberates 3-pentenal when hydrogen is added. It also represents the most stable intermediate under real hydroformylation conditions and exists in high concentrations during the catalysis. The rate law of the reaction is found to be second-order in syngas pressure and independent of the butadiene concentration. This agrees with the total barrier between the η3-crotyl complex and one of the transition states of hydrogen addition or reductive elimination being rate determining. The olefin insertion step is found to be partly reversible depending on the pressure, which means that n/iso regioselectivity is not controlled by this step alone.

Synthesis and Characterization of Crotyl Intermediates in Rh-Catalyzed Hydroformylation of 1,3-Butadiene

Crotyl rhodium complexes like (κ2-L)Rh(η3-crotyl) and (κ2-L)Rh(η3-crotyl)(CO) (L = chelating phosphorus ligand) are important intermediates in hydroformylation catalysis of butadiene and related reactions. They are assumed to be responsible for the specific reactivity patterns of conjugated dienes. We prepared and characterized by X-ray crystallography several of these complexes with novel chelating bisphosphite ligands. (κ2-L)Rh(η3-crotyl) complexes exhibit a square-planar geometry, while their CO adducts (κ2-L)Rh(η3-crotyl)(CO) are trigonal-bipyramidal with the bisphosphite ligand in ee-bonding mode. Typically, the η3-crotyl unit can be oriented in several diastereomeric ways, of which oftentimes two or more are present in solution and in the solid state.

Density Functional Investigations of the Rh-Catalyzed Hydroformylation of 1,3-Butadiene with Bisphosphite Ligands

The catalytic cycle of the Rh-catalyzed monohydroformylation of 1,3-butadiene with a triptycene-derived bisphosphite ligand was investigated with density functional theory, as it determines the selectivity of the 1,4-bis-hydroformylation of 1,3-butadiene to adipic aldehyde, a dream reaction of chemical industry. Out of the variety of possible reactive pathways, two dominant ones were highlighted leading to the monoaldehydes 3-pentenal and 4-pentenal, which experimentally also are the main primary products. With catalysts like the one studied here, which are highly n-selective and reactive for 1-alkene hydroformylation, 4-pentenal is known to be exclusively converted to the bis-hydroformylation product adipic aldehyde. An η3-crotyl complex formed by iso-insertion of an (η2-butadiene)Rh(H) species, not involved in hydroformylation reactions of 1-alkenes and requiring a slightly smaller activation barrier than the desired n-insertion, could be identified as an important intermediate for the monohydroformylation of butadiene. Once formed, this η3-crotyl species opens up an unproductive exit channel within the catalytic reaction mechanism, which does not lead to adipic aldehyde. Free energy profiles in solution were calculated in order to find the intermediates and transition states that govern turnover frequency (TOF) and selectivity: The Rh crotyl complex and the reductive elimination transition state most likely limit the TOF, while the prediction of the regioselectivity is more complicated and depends on several steps.

Scalable and chromatography-free synthesis of 2-(2-formylalkyl)arenecarboxylic acid derivatives through the supramolecularly controlled hydroformylation of vinylarene-2-carboxylic acids.

This protocol describes how to prepare 2-(2-formylalkyl)-arenecarboxylic acid derivatives, common building blocks for the synthesis of various valuable chemicals (e.g., anti-obesity and Alzheimer's disease treatment pharmaceuticals), by using the fully regioselective hydroformylation of vinyl arene derivatives. This catalytic reaction proceeds cleanly with 100% regioselectivity and chemoselectivity. The procedure is reliably scalable and can be efficiently conducted on a multigram scale. The analytically pure product is easily isolated with a nearly quantitative yield by using a simple acid-base extraction workup and avoids any tedious chromatography. This protocol details the synthesis of a bisphosphite ligand (L1) that is a pivotal element of the catalytic system used, Rh(acac)(CO)2 with ligand L1, starting from commercial building blocks. The protocol also describes a general procedure for the preparative hydroformylation of vinylarene-2-carboxylic acid derivatives to 2-formylalkylarene products, providing a representative example for the hydroformylation of 2-vinylbenzoic acid (1a) to 2-(3-oxopropane)-benzoic acid (2a). The synthesis of L1 (six chemical reactions) uses 2-nitrophenylhydrazine, 4-benzyloxybenzoylchloride and (S)-binol, and takes 5-7 working days. The actual hydroformylation reaction of each vinyl arene derivative takes ∼4 h of active effort over a period of 1-3 d.

Inter- and Intramolecular Interactions in Triptycene-Derived Bisphosphite Hydroformylation Catalysts: Structures, Energies, and Caveats for DFT-Assisted Ligand Design

The hydroformylation catalyst (L)RhH(CO)2, with a triptycene-derived bisphosphite ligand, and its iridium analogue were studied in solution, in the solid state, and computationally (DFT) in order to determine their molecular structures and to understand the equilibria between isomers. The predicted intramolecular distance of the two biphenyl side groups of these ligands strongly depends upon the treatment of inter- and intramolecular noncovalent interactions. A balanced treatment of these “weak” interactions is a prerequisite for obtaining reasonable structures and consequently also for determining relative energies of the different P-coordination modes. Low-temperature NMR studies confirm the equilibrium between axial–equatorial and equatorial–equatorial isomers in solution and have been used to estimate their relative stability in the equilibrium.

Large-bite bisphosphite, 1,3-C 6H 4{OPOC 10H 6(μ-S)C 10H 6O} 2: Synthesis, copper(I), and gold(I) complexes

Large-bite bisphosphite ligand 1,3-C 6H 4{OPOC 10H 6(μ-S)C 10H 6O} 2 ( 3), is obtained by reacting chlorophosphonite {OC 10H 6(μ-S)C 10H 6O}PCl ( 2) with resorcinol in the presence of triethylamine. Treatment of 3 with CuCl in 1:1 molar ratio produces a 1D-coordination polymer [CuCl{(–OC 10H 6(μ-S)C 10H 6O–)P(–OC 6H 4O–)P(–OC 10H 6(μ-S)C 10H 6O–)}-κP,κP] ∞ ( 4) in good yield. Similar reaction of 3 with two equivalents of AuCl(SMe 2) affords a dinuclear complex, [Au 2Cl 2{(–OC 10H 6(μ-S)C 10H 6O–)P(–OC 6H 4O–)P(–OC 10H 6(μ-S)C 10H 6O–)}-κP,κP] ( 5). Single crystal X-ray structures of the ligand 3 and the complexes 4 and 5 are reported. The gold complex 5 shows dimeric structure supported by strong Au···Au aurophilic interactions.

Calix[4]arene bisphosphite ligands bearing two distal 2,2′-biphenyldioxy or 2,2′-binaphthyldioxy moieties: conformational flexibility and allyl–palladium complexes

Achiral and chiral calix[4]arene bisphosphite ligands ( 2 and 3) bearing two distal 2,2′-biphenyldioxyphosphinoxy and 2,2′-binaphthyldioxyphosphinoxy moieties, respectively, have been synthesized. Each of these ligands exists in two pairs of interconverting conformations in solution. The partial cone conformer (A) of the (bis)biphenyldioxyphosphinoxy ligand 2 has been separated by fractional crystallization and its structure established by X-ray crystallography. The mechanism of interconversion of the pairs of conformers (A/B and C/D) has been probed by two-dimensional NMR spectroscopy. The 1H and 31P NMR evidence strongly supports a similar kind of exchange mechanism for ligand 3. Freezing of the cone conformer from the interconverting C/D pair of conformers of ligand 2 has been achieved by complexation with (allyl)palladium moieties. The methyl–allyl complex ( 2d) is moderately effective for catalytic regioselective allylic alkylation of crotyl acetate.

Phosphite ligands derived from distally and proximally substituted dipropyloxy calix[4]arenes and their palladium complexes: Solution dynamics, solid-state structures and catalysis

Two bisphosphite ligands, 25,27-bis-(2,2′-biphenyldioxyphosphinoxy)-26,28-dipropyloxy- p-tert-butyl calix[4]arene ( 3) and 25,26-bis-(2,2′-biphenyldioxyphosphinoxy)-27,28-dipropyloxy- p-tert-butyl calix[4]arene ( 4) and two monophosphite ligands, 25-hydroxy-27-(2,2′-biphenyldioxyphosphinoxy)-26,28-dipropyloxy- p-tert-butyl calix[4]arene ( 5) and 25-hydroxy-26-(2,2′-biphenyldioxyphosphinoxy)-27,28-dipropyloxy- p-tert-butyl calix[4]arene ( 6) have been synthesized. Treatment of (allyl) palladium precursors [(η 3-1,3-R,R′-C 3H 4)Pd(Cl)] 2 with ligand 3 in the presence of NH 4PF 6 gives a series of cationic allyl palladium complexes ( 3a– 3d). Neutral allyl complexes ( 3e– 3g) are obtained by the treatment of the allyl palladium precursors with ligand 3 in the absence of NH 4PF 6. The cationic allyl complexes [(η 3-C 3H 5)Pd( 4)]PF 6 ( 4a) and [(η 3-Ph 2C 3H 3)Pd( 4)]PF 6 ( 4b) have been synthesized from the proximally (1,2-) substituted bisphosphite ligand 4. Treatment of ligand 4 with [Pd(COD)Cl 2] gives the palladium dichloride complex, [PdCl 2( 4)] ( 4c). The solid-state structures of [{(η 3-1-CH 3-C 3H 4)Pd(Cl)} 2( 3)] ( 3f) and [PdCl 2( 4)] ( 4c) have been determined by X-ray crystallography; the calixarene framework in 3f adopts the pinched cone conformation whereas in 4c, the conformation is in between that of cone and pinched cone. Solution dynamics of 3f has been studied in detail with the help of two-dimensional NMR spectroscopy. The solid-state structures of the monophosphite ligands 5 and 6 have also been determined; the calix[4]arene framework in both molecules adopts the cone conformation. Reaction of the monophosphite ligands ( 5, 6) with (allyl) palladium precursors, in the absence of NH 4PF 6, yield a series of neutral allyl palladium complexes ( 5a– 5c; 6a– 6d). Allyl palladium complexes of proximally substituted ligand 6 showed two diastereomers in solution owing to the inherently chiral calix[4]arene framework. Ligands 3, 6 and the allyl palladium complex 3f have been tested for catalytic activity in allylic alkylation reactions.

Diastereoisomeric bisphosphite ligands in the hydroformylation of octenes: rhodium catalysis and HP-NMR investigations

Diastereoisomeric hydroformylation catalysts show differences for the catalyst preformation pathway and a strongly reduced n-octene hydroformylation activity for the (S,S,R)-isomer.

Ligands for Practical Rhodium-Catalyzed Asymmetric Hydroformylation

A series of bis-phosphite and bis-phosphine ligands for asymmetric hydroformylation reactions has been evaluated. Bis-phosphite ligands lead, in general, to high regioselectivities across a range of substrates while good enantioselectivities are limited to only a few examples. We found that bis-phospholane-type ligands, such as bis-diazaphospholanes and bis-phospholanes, can lead to very high regio- and enantioselectivities for several different substrates.

Effect of the Dihedral Angle of Biaryl-Bridged Bisphosphite Ligands on Enantioselectivity and Regioselectivity of Asymmetric Hydroformylation

Eight new biaryl-bridged bisphosphite ligands have been synthesized and applied in rhodium-catalyzed asymmetric hydroformylation of styrene, allyl cyanide, and vinyl acetate. X-ray crystallographic studies of square planar LRh(acac) complexes of four of these bisphosphite ligands revealed that the dihedral angle of the bridging biaryl moiety depends on its identity and lies between 59.8° and 80.0°. A correlation between the dihedral angle in these Rh complexes and hydroformylation enantioselectivity and regioselectivity for both allyl cyanide and vinyl acetate is reported. Smaller dihedral angles were found to lead to increased regio- and enantioselectivity. Density functional theory calculations of a five-coordinate model complex (LRh(CO)2H) show that decreased dihedral angles lead to smaller P−Rh−P bite angles. Although large bite angles have previously been correlated with increased hydroformylation regioselectivity, these results provide the first demonstration of a bite angle effect on enantioselecti...

Parallel ligand screening on olefin mixtures in asymmetric hydroformylation reactions.

[reaction: see text] Herein we describe a new protocol for catalyst evaluation in asymmetric hydroformylation reactions where multisubstrate screening is performed in an array of parallel reactors. This method was successfully demonstrated using a mixture of styrene, allyl cyanide, and vinyl acetate. Using this screening methodology, a set of phosphite ligands was evaluated and led to the discovery of a bisphosphite ligand that gave 88% ee and unprecedented >100:1 branched:linear regioselectivity in asymmetric hydroformylation of vinyl acetate.

Synthesis and application of a new bisphosphite ligand collection for asymmetric hydroformylation of allyl cyanide.

A series of mono- and bidentate phosphites was prepared with (S)-5,5',6,6'-tetramethyl-3,3'-di-tert-butyl-1,1'-biphenyl-2,2'-dioxy [(S)-BIPHEN] as a chiral auxiliary and screened in the asymmetric hydroformylation of allyl cyanide. These hydroformylation results were compared with those of two existing chiral ligands, Chiraphite and BINAPHOS, whose utility in asymmetric hydroformylation has been previously demonstrated. Bisphosphite 11 with a 2,2'-biphenol bridge was found to be the best overall ligand for asymmetric hydroformylation of allyl cyanide with up to 80% ee and regioselectivities (branch-to-linear ratio, b/l) of 20 with turnover frequency of 625 [h(-)(1)] at 35 degrees C. BINAPHOS gave enantioselectivities up to 77% ee when the reaction was conducted in either acetone or neat but with poor regioselectivity (b/l 2.8) and activities 7 times lower than that of 11. The product of allyl cyanide hydroformylation using (R,R)-11 was subsequently transformed into (R)-2-methyl-4-aminobutanol, a useful chiral building block. Single-crystal X-ray structures of (S,S)-11 and its rhodium complex 19 were determined.

Sterically Congested Bisphosphite Ligands for the Rhodium(I)-Catalyzed Hydrosilation of Ketones

Sterically congested bisphosphites were shown to be effective ligands for the Rh-catalyzed hydrosilation of ketones with diphenylsilane. The hydrosilation of 4-alkylcyclohexanones and ( m )-menthone led to a significant proportion of the less stable (axial) alcohol, which suggests that these reactions are under kinetic, rather than thermodynamic, control.

X-ray crystal structure of cis-{(±)-6,6′-[[1,1′-biphenyl]-2,2′-diylbis(oxy)]bis–dibenzo[d,f][1,3,2]dioxaphosphepin} diiodoplatinum(II)·dichloromethane

Bis(dibenzo[d,f][1,3,2]dixoaphosphepin) ligands are extensively used in catalysts for asymmetric alkene hydroformylation; however, few crystal structures of complexes of these ligands have been reported. In this paper, the synthesis and X-ray crystal structure of cis-{(±)-6,6′-[[1,1′-biphenyl]-2,2′-diylbis(oxy)]bis-dibenzo[d,f][1,3,2]dioxaphosphepin} diiodoplatinum (II)·dichloromethane are presented. This complex crystallizes in the triclinic space group P1¯ with a = 12.0842(2,3) b = 12.6993(15) c = 13.2801(18) A; α = 85.852(10), β = 76.723(13), γ = 72.400(12)°, V = 1890.7(10) A3 and Z = 4. The diastereomer that has crystallized has an R*R*R*(S*S*S*) configuration. This X-ray crystal structure supports previous observations that bis(phosphite) ligands with bridging groups derived from 2,2′-biphenol can exhibit a wide range of bite angles (>20°).