Catalyst Precursors For Hydroformylation Research Articles

Rhodium(I) metallacycles based on alkylated-PTA scaffolds: Synthesis and evaluation as hydroformylation catalyst precursors

A series of rhodium(I) metallacycles based on alkylated PTA complexes were synthesised and fully characterised using a range of spectroscopic and analytical techniques. These mononuclear Rh(I) complexes were evaluated in the aqueous biphasic (water-toluene) hydroformylation of 1-octene, showing chemoselectivity to aldehydes.

Synthesis, characterization and evaluation of heterobimetallic Fe(II)/Rh(I) and Fe(II)/Ru(II) complexes as catalyst precursors for hydroformylation of 1-octene

Two new ferrocenyl iminopyridyl ligands, L1 and L2, have been synthesized and characterized using spectroscopic and analytical techniques. Both ligands were used to prepare new Rh(I) and Ru(II) ferrocenyl complexes 1–4. The structures of the complexes were confirmed using 1H and 13C nuclear magnetic resonance spectroscopy, high resolution electrospray ionization mass spectrometry, and infrared spectroscopy. The complexes were tested as catalysts in the hydroformylation of 1-octene. Rh ferrocenyl complexes 1 and 4 produced aldehydes under mild conditions while the Ru-ferrocenyl complexes 2 and 3 required higher temperature and pressure for effective hydroformylation to occur. The catalysts display excellent aldehyde chemoselectivity with varying regeoselectivity depending on temperature and pressure conditions employed. At high temperatures, the Rh ferrocenyl precatalysts favor formation of branched aldehydes due to increased isomerization at high temperatures. The Ru ferrocenyl precatalysts displayed less hydroformylation activity; however, the complexes show good chemoselectivity for aldehydes with no hydrogenation products formed.

Rhodium(I) Ferrocenylcarbene Complexes: Synthesis, Structural Determination, Electrochemistry, and Application as Hydroformylation Catalyst Precursors

New examples of the rare class of rhodium(I) ferrocenyl Fischer carbene complexes 1–8, [Rh(LL)Cl{C(XR)Fc}] [LL = cod, (CO)2, (CO, PR3) (R = Ph, Cy or OPh), and (CO, AsPh3); XR = OEt or NHnPr] were prepared, and the electronic effects of coligands and alkoxy vs aminocarbene substituents were investigated by spectroscopic and electrochemical methods. The molecular structures of complexes 1, 2, and 4–6 were confirmed by single-crystal X-ray diffraction. The use of the complexes 1–8 as homogeneous catalysts for the hydroformylation of 1-octene was demonstrated, and the influence of the carbene substituents and coligands on the activity and regioselectivity of the catalysts evaluated. Finally, the stability of the Rh–Ccarbene bond of complex 1 under hydroformylation conditions was confirmed with 13C NMR experiments.

Immobilized bisdiazaphospholane catalysts for asymmetric hydroformylation.

Condensation reactions of enantiopure bis-3,4-diazaphospholanes (BDPs) that are functionalized with carboxylic acids enable covalent attachment to bead and silica supports. Exposure of tethered BDPs to the hydroformylation catalyst precursor, Rh(acac)(CO)2, yields catalysts for immobilized asymmetric hydroformylation (iAHF) of prochiral alkenes. Compared with homogeneous catalysts, catalysts immobilized on Tentagel resins exhibit similarly high regioselectivity and enantioselectivity. When corrected for apparent catalyst loading, the activity of the immobilized catalysts approaches that of the homogeneous analogues. Excellent recyclability with trace levels of rhodium leaching are observed in batch and flow reactor conditions. Silica-bound catalysts exhibit poorer enantioselectivities.

Water‐Soluble Half‐Sandwich RuII–Arene Complexes: Synthesis, Structure, Electrochemistry, DFT Studies, and Aqueous Phase Hydroformylation of 1‐Octene

AbstractWater‐soluble mononuclear ruthenium complexes containing monodentate P‐donor ligands [1,3,5‐triaza‐7‐phosphaadamantane (PTA) and P(OMe)3], together with a mononuclear bidentate salicylaldimine ruthenium–arene complex, were synthesized from a water‐soluble dimeric ruthenium(II)–arene precursor. These complexes were used as catalyst precursors in the aqueous biphasic hydroformylation of 1‐octene. Hydroformylation reactions with these Ru‐arene complexes showed that the complexes are active hydroformylation catalyst precursors in water. The catalyst precursors convert 1‐octene into a range of products, which include aldehydes and alcohols, as well as isomerization and hydrogenation products. The less basic the ligand, the more it favoured the production of aldehydes. The relative basicity of the ligands P(OMe)3, PTA and the N,O‐chelating ligand was elucidated by cyclic voltammetry and supported by DFT calculations. The catalysts show good recyclability without a significant decrease in 1‐octene conversion. All of the catalysts could be reused three times.

Synthesis of neutral rhodium(I) complexes containing a rigid P–O ligand and their use as catalyst precursors for the hydroformylation of 1-hexene

The first rhodium complexes with the anionic 2-(bis(2-methoxyphenyl)phosphino)benzenesulfonate ( L) ligand have been synthesized and characterized. Selected complexes have been used as catalyst precursors for the homogeneous hydroformylation of 1-hexene, which has been carried out in preparative autoclaves and studied under operando conditions by means of both high-pressure NMR (HPNMR) and high-pressure IR (HPIR) spectroscopy. Operando spectroscopic hydroformylation experiments have shown that the catalyst precursors bearing either 1,5-cyclooctadiene or triethylamine as ancillary ligand are rapidly converted into di-carbonyl complexes. Rhodium(I) mono-and di-carbonyl complexes have been shown to be resting states of the catalytic cycle, most likely in equilibrium with other species containing either the zwitterionic ligand HL coordinated in the κ 1- O bonding mode or exclusively carbonyl ligands.

Time-resolved infrared study of reactive species produced by flash photolysis of the hydroformylation catalyst precursor Co 2(CO) 6(PMePh 2) 2

Flash photolysis with time-resolved infrared (TRIR) spectroscopy was used to elucidate the photochemical reactivity of the hydroformylation catalyst precursor Co 2(CO) 6(PMePh 2) 2. Depending on reaction conditions, the net products of photolysis varied significantly. A model is presented that accounts for the net reactivity with two initial photoproducts, the 17-electron species Co(CO) 3(PMePh 2) and the coordinatively unsaturated dimer Co 2(CO) 5(PMePh 2) 2. No evidence was found for photochemical formation of Co 2(CO) 6(PMePh 2). Time-resolved spectroscopic studies allowed for the direct observation of transient species and for kinetics studies of certain reactions; for example, the reactions of Co(CO) 3PMePh 2 with CO and with PMePh 2 gave the respective rate constants 1.5 × 10 5 and 1.2 × 10 7 M −1 s −1, while the analogous reactions with Co 2(CO) 5(PMePh 2) 2 gave the rate constants of 2.6 × 10 6 M −1 s −1 and 3.9 × 10 7 M −1 s −1.

Mechanistic studies on the formation of Pt(II) hydroformylation catalysts in imidazolium-based ionic liquids

The kinetics of the formation of the active species cis-[Pt II(PPh 3) 2Cl(SnCl 3)] and cis-[Pt II(PPh 3) 2(SnCl 3) 2] from the hydroformylation catalyst precursor cis-[Pt II(PPh 3) 2Cl 2] in the presence of SnCl 2, was studied in two different imidazolium-based ionic liquids. A large range of different chlorostannate melts consisting of 1-butyl-3-methyl-imidazolium cations and [Sn x Cl y ] (− y + 2 x) anions with varying molar fraction of SnCl 2, were prepared and characterized by 1H and 119Sn NMR. The observed chemical shifts point to major changes in the composition of the anionic species within the melt. The second ionic liquid employed, viz., 1-butyl-3-methyl-imidazolium-bis(trifluormethylsulfonyl)amide was prepared in a colorless quality that enabled its application in kinetic studies. The concentration and temperature dependence of the substitution of Cl − by [SnCl 3] − to yield cis-[Pt II(PPh 3) 2Cl(SnCl 3)], could be studied in detail. Theoretical (DFT) calculations were employed to model the reaction progress and to resolve the role of the ionic liquid in the activation of the catalyst. The available results are presented and a plausible mechanism for the formation of the catalytically active species is suggested.

Rhodium(I) fluorothiolate complexes as hydroformylation catalyst precursors. Crystal structure of two polymorphs of trans-[Rh(SC 6F 5)(CO)(PPh 3) 2

The perfluorothiolate dinuclear compounds [Rh( μ-SC 6F 5)(COD)[ 2 1 and [Rh( μ-SC 6F 5)(CO) 2[ 2 2 react with PPh 3 to give monomeric and dimeric complexes, the particular product depending upon the PR 3/Rh ratio and reaction conditions. Reaction of 2 with 2 moles of PPh 3 renders cis- 7 and trans-[Rh( μ-SC 6F 5)((CO)(PPh 3)[ 2 8, while with 4 moles of PPh 3 trans[Rh(SC 6F 5)(CO)(PPh 3) 2[ 10a is obtained. This latter product can otherwise be prepared by Cl metathesis from trans-[RhCl(CO(PPh 3) 2[ in toluene. This same reaction in dichloromethane however yields the cis isomer 10b. When a larger excess of PPh 3 is used, a mixture of compounds 11a and 11b is formed. An X-ray crystal structure study shows trans[Rh(SC 6F 5)(CO)(PPh 3) 2[ to exit as two polymorphs. 11a crystallises in the space group P2 1/n of the monoclinic system with a = 12.489(1), b = 15.430(5), c = 19.719(1) Å, α = γ = 90, β = 92.84(1)°, and 11b is triclinic, space group P1¯ with a = 9.764(2), b = 12.197(6), c = 17.880 Å, α = 100.18(5), β = 101.92(2), γ = 113.61(2)°. Both PPh 3 ligands are mutually trans and the difference in v(CO) stretching frequencies 1989 and 1939 cm −1, can be explained in terms of o-phenyl H…CO interactions in the latter. The [Rh( μ-SC 6F 5)(COD)[ 2 1 and [Rh( μ-SC 6F 5)(CO) 2[ 2 2/nPPh 3 systems have been studied as catalyst precursors for the hydroformylation of 1-heptene in toluene at 30 bar and 343 K. Selectivity towards the linear aldehyde is enhanced when dimeric complexes are used.

Synthesis, structure and reactivity of a novel bis(phosphite) tetrarhodium decacarbonyl hydroformylation catalyst precursor

Abstract The tetranuclear Rh4(μ-bpnap)(CO)10 (1) was synthesized in 68% yield by the reaction of Rh2(CO)4C12 with bpnap (2,2′-bis[(1,1'-biphenyl-2,2′-diyl)phosphite]-1,1′-binaphthyl) (2) under CO. The crystal structure of 1, determined by X-ray diffraction, established that the bpnap ligand bridged two rhodium atoms of a tetrahedral metal framework. Recrystallization of 1 from CH2Cl2/THF led to its partial conversion to a structural isomer, la, which was characterized by solution spectroscopic methods. The reaction of Rh(acac)(CO)2 and bpnap under 1:1 CO/H2 led to a mixture of products consisting of 1, la and at least two hydridic compounds. The latter were also formed by the hydrogenation of Rh(acac)(CO)2 and bpnap. Rh4(μ-bpnap)(CO)10 was shown to be an effective catalyst precursor for the isomerization and hydroformylation of 1-octene, giving, for the latter reaction, moderate linear/branched selectivity for the product aldehydes. The hydroformylation of a-methylstyrene with Rh(acac)(CO)2 and R-(+)-bpnap gave essentially no enantiomeric excess of 3-phenylbutanal. The structural features of 1, along with comparison of its reactivity with other bis(phosphite) metal complexes are discussed. Crystal data for Rh4(bpnap)(CO)10 (1) (f.w. 1577.48): monoclinic, P21/c; a = 14.624(4), b = 18.974(6), c = 21.343(5)A; V= 5899(5)A; β = 95.06(2)°, Z= 4; R = 6.4%.

Impact of dioxygen and carboxylic acids on the transformation of rhodium(I) to rhodium(III) complexes

The reaction of the hydroformylation catalyst precursor [Rh(acac)(CO)(PPh3)](acac = acetylacetonate) with dioxygen and salicylic acid led to the formation of the rhodium(III) complexes [Rh(acac)(HOC6H4CO2)2(PPh3)(H2O)] and [Rh(acac)2(HOC6H4CO2)(PPh3)]. The structures of the latter complexes were characterized spectroscopically (1H and 31P NMR) as well as by X-ray crystallography. Dioxygen activation by Rh1 proceeds through peroxo [Rh(O2)(HOC6H4CO2)(CO)(PPh3)] and hydrogen dioxide [Rh(O2H)(acac)(HOC6H4CO2)(CO)(PPh3)] complexes identified by IR UV/VIS and 31P NMR methods. Oxidation of CO to CO2 occurs in the inner co-ordination sphere of rhodium.

Role of the trichlorostannyl ligand in homogeneous catalysis. 2. Spectroscopic studies of the reaction of cis-[PtCl2(CO)(PR3)] with tin dichloride dihydrate (SnCl2.2H2O): ligand rearrangement reactions in the formation of an olefin hydroformylation catalyst precursor

Role of the trichlorostannyl ligand in homogeneous catalysis. 2. Spectroscopic studies of the reaction of cis-[PtCl2(CO)(PR3)] with tin dichloride dihydrate (SnCl2.2H2O): ligand rearrangement reactions in the formation of an olefin hydroformylation catalyst precursor

Cationic complexes of rhodium(I) with phenanthroline type ligands

Complexes [Rh(COD)(L-L)]ClO4 are prepared by reaction of [Rh(COD)2]ClO4 with the appropriate ligand L-L (4,7-Ph2Phen, 2,9-Me2-4,7-Ph2Phen, 2,9-Me2Phen or 5,6-Me2Phen). Treatment of these complexes with carbon monoxide gives [Rh(CO)2(L-L)]ClO4. When the carbonylation reaction is performed in the presence of P(4-RC6H4)3, pentacoordinate complexes [Rh(CO)(L-L){P(4-RC6-H4)}32]ClO4 (R=Me, H, F or Cl) are formed. The use of [Rh(COD)(L-L)]ClO4 as homogeneous hydroformylation catalyst precursors was studied (50 atm, 80°C). Under these conditions no hydrogenation of the olefin or of the aldehydes is observed, but isomerisation reactions are significant.

Pyrazolate rhodium complexes as hydroformylation catalyst precursors

Pyrazolate rhodium complexes as hydroformylation catalyst precursors