Rhodium phosphine complexes immobilized on silica as active catalysts for 1-hexene hydroformylation and arene hydrogenation

In immobilizing the rhodium complexes [Rh(acac)(CO)(P)] (1) and [Rh(acac)(P)₂] (2) (P = Ph₂PCH₂CH₂Si(OMe)₃) onto SiO₂, acetylacetone is found to be released through protonation of the acac ligand by the acidic silica-OH groups. The resulting complexes [Rh(O-{SiO₂}(HO-{SiO₂})(CO)(P-{SiO₂})] (1a) and [Rh(O-{SiO₂})(HO-{SiO₂})(P-{SiO₂})₂] (2a) were successfully tested with respect to their catalytic action on 1-hexene hydroformylation as well as benzene and toluene hydrogenation. The reaction outcome, viz. the formation of aldehydes versus isomerization, depends strongly on the presence and concentration of a phosphine co-catalyst. Thus, while 1a gave only a 17% yield of aldehyde in the absence of phosphines, the yield is increased to 54% in the presence of phosphinated silica P-{SiO₂} or even 94% if PPh₃ is added to the solution. Without extra added phosphine, both 1a and 2a effect mainly the isomerization of 1-hexene to 2-hexene. Pre-catalyst 1a catalyzes also the hydrogenation of benzene at 10.5 atm H₂ and 90 °C to give cyclohexane with a TOF of 608 h⁻¹.     

Rhodium catalyzed hydroformylation of 2-phenylsulfonylbicyclo[2.2.1] alkenes: effect of the phenylsulfonyl group

The preliminary results of the hydroformylation of 2-phenylsulfonyl substituted norbornene and norbornadiene derivatives catalyzed by the unmodified Rh(CO)₂acac system are presented. The reaction, occurring under standard oxo conditions, gives polyfunctionalized exo norbornene- and exo norbornanecarboxaldehydes. The effect of the phenylsulfonyl group has been evaluated: it has been found that the steric properties of the sulfonyl substituent, more than the electronic ones, influence the regioselectivity of the process.     

Rhodium complexes with dioximes as catalysts of hydroformylation and hydrogenation of 1-hexene

Rhodium(II) complexes with dioximes [Rh(Hdmg)₂(PPh₃)]₂ [I] (Hdmg=monoanion of dimethylglyoxime) and [Rh(Hdmg)(ClZndmg)(PPh₃)]₂ [II] catalyse hydroformylation and hydrogenation reactions of 1-hexene at 1 MPa CO/H₂ and 0.5 MPa H₂ at 353 K, respectively. Hydroformylation with complex [I] produces 94% of aldehydes (n/iso=2.2) and 6% 2-hexene whereas the second catalyst [II] gives ca. 40% of aldehydes (n/iso=2.1) and 60% of 2-hexene. Corresponding Rh(III) complexes are inactive in hydroformylation except of RhH(Hdmg)₂(PPh₃) [III], which shows activity similar to [I]. Complexes [Rh(Hdmg)₂(PPh₃)]₂ [I], [Rh(Hdmg)(ClZndmg)(PPh₃)]₂ [II], RhH(Hdmg)₂(PPh₃) [III] and [Rh(Hdmg)₂(PPh₃)₂]ClO₄ [V] catalyse 1-hexene hydrogenation with an average TON ca. 18 cycles/mol [Rh]×min. Complex [II] has also been found to catalyse hydrogenation of cyclohexene, 1,3-cyclohexadiene and styrene.     

编织芳基网络聚合物负载Rh催化剂上高碳烯烃氢甲酰化反应性能

考察了编织芳基网络聚合物（KAPs）负载的Rh催化剂（Rh/KAPs）在高碳烯烃氢甲酰化反应中的催化性能. 结果表明,三苯基膦-苯基底KAPs负载Rh催化剂（Rh/KAPs-1）具有优异的高碳烯烃氢甲酰化反应活性,产物醛收率显著高于Rh/SiO₂催化剂. 傅里叶变换红外光谱、热重、氮气吸附-脱附、X射线衍射、透射电子显微镜、¹³C核磁共振和³¹P核磁共振结果显示,Rh/KAPs-1催化剂具有优异的热稳定性及大的比表面积和多级孔道结构,Rh颗粒处于高度分散状态,并可在反应过程中形成均相催化活性物种.     

Unique selectivity for the dimerization of propene on RhSn/SiO2 catalysts: implications on the mechanism of C---C bond formation and cleavage on bimetallic catalysts

A series of bimetallic catalysts RhSn_x/SiO₂ (x = 0.4, 0.7, 0.9, and 1.4) were synthesized by the reaction of the monometallic catalyst Rh/SiO₂ with Sn(n-butyl)₄ under hydrogen. Various chemical and spectroscopic methods indicated that the metals present were fully reduced, and that tin atoms rest on the surface, very slightly increasing particle size and producing isolated rhodium sites. The catalytic reactions of propylene/hydrogen mixtures in the presence of these bimetallic catalysts are compared with those of the monometallic Rh/SiO₂ catalysts. The mechanistically interesting reactions observed are those of carbon-carbon bond formation and cleavage. For the monometallic catalyst, olefin homologation and hydrogenolysis were observed, reactions which invoked the transfer of C₁ fragments from one olefin to another. For the bimetallic catalysts, a marked increase in the selectivity for C₆ products was observed. The presence of hydrogen is necessary to this reaction but selectivity for C₆ is enhanced when hydrogen is in deficit with respect to propylene. Selectivity for C₆ increases with the surface rhodium to tin, Rh^s/Sn, ratio to a maximum at 0.9. Low temperature favors the formation of C₆ and C₂ products.     

Rhodium-catalyzed hydroformylation of C6 alkenes and alkene mixtures - a comparative study in homogeneous and aqueous-biphasic media using PPh3, TPPTS and TPPMS ligands

The complexes RhH(CO)L₃, where L = PPh₃, P(m-C₆H₄SO₃Na)₃ (TPPTS), and (C₆H₅)₂P(m-C₆H₄SO₃Na) (TPPMS) were used as catalyst precursors for a comparative study of the catalytic hydroformylation of several C6 alkenes and alkene mixtures under moderate reaction conditions in homogeneous (PPh₃) and aqueous-biphasic (TPPTS, TPPMS) media. The biphasic systems are efficient for the hydroformylation of hex-1-ene, 2,3-dimethyl-1-butene, styrene, cyclohexene, and mixtures thereof, in water/n-heptane at 80 °C. The main problem associated with these catalysts is their tendency to promote alkene isomerization if the effective syngas concentration in the liquid phases is low, but this side-reaction can be suppressed by using higher CO/H₂ pressures (54 atm). The selectivity of both water-soluble catalysts for linear products of hex-1-ene and for branched products of styrene is modest in comparison with the homogeneous system, which may limit their utility for classical oxo uses, but this is not a disadvantage for other interesting applications related to the hydroformylation of alkene mixtures and particularly to naphtha upgrading where linear and branched products are equally useful. The catalysts can be recycled without significant loss of activity and are resistant to the presence of benzothiophene in the mixture.     

Rhodium(I) complexes with 1′-(diphenylphosphino)ferrocenecarboxylic acid as active and recyclable catalysts for 1-hexene hydroformylation

The rhodium complex trans-[Rh(CO)(Hdpf-κP)(dpf-κ²O,P)] (1), (Hdpf = 1′-(diphenylphosphino)ferrocenecarboxylic acid) was used as an efficient and recyclable catalyst for 1-hexene hydroformylation producing ca. 80% of aldehydes at 10 atm CO/H₂ and 80 °C. After the reaction, unchanged complex 1 was separated from the reaction mixture and used again three times with the same catalytic activity. The effect of modifying ligands, phosphines and phosphites, on the reactivity of 1 was investigated. The active catalytic systems containing 1 or trans-[Rh(CO)(L)(dpf-κ²O,P)] (2) were formed in situ from acetylacetonato rhodium(I) precursors [Rh(CO)₂(acac)] (3) or [RhL(CO)(acac)] (4) and Hdpf or Medpf (L = phosphine, Medpf = methyl ester of Hdpf).     

Ruthenium-catalyzed one-pot hydroformylation of alkenes using carbon dioxide as a reactant

A new hydroformylation of alkenes using carbon dioxide as a reactant is shown to take place in the presence of ruthenium cluster complexes and halide salts. Similar or even better yields of alcohols were formed as compared to the conventional hydroformylation with CO under the same reaction conditions. The reaction proceeded in three steps: CO₂ is first converted to CO; then it is used as a reagent for hydroformylation to give aldehyde; subsequently, it is hydrogenated to alcohol. ESI-mass spectrometric analyses of the reaction solutions indicated formation of four kinds of ruthenium anionic complexes including tetra-, tri-, and mononuclear species. On the basis of experimental findings, possible roles of these complexes are discussed.     

Behaviour of water-soluble dinuclear rhodium complexes in the hydroformylation reaction of oct-1-ene

The biphasic hydroformylation reaction of oct-1-ene, has been investigated by using the water-soluble dinuclear complex [Rh₂(μ-S^tBu)₂(CO)₂(TPPTS)₂] as precursor. Addition of ethanol as a cosolvent dramatically improved the yields but the good regioselectivity in linear aldehyde observed for neat oct-1-ene—water systems (97%) decreased to 83% (for 22% ethanol w/w). It is shown that the dinuclear framework cannot be maintained, that the mononuclear complex [RhH(CO)(TPPTS)₃] is formed, and that thiol and significant amounts of [Rh₂(μ-S^tBu)₂(CO)₄] move into the organic phase. This reaction from the dinuclear species requires the simultaneous presence of water and carbon monoxide. Introduction of the water-soluble thiol HS(CH₂)₃NMe₂ in the bridging positions affords the complex [Rh₂(μ-S(CH ₂)₃NHMe₂)₂(CO)₂(TPPTS)₂]Cl₂ which can be kept in the aqueous hase but has a low level of catalytic activity.     

Novel α-fluorinated cyclic phosphite and phosphinite ligands and their Rh-complexes as suitable catalysts in hydroformylation

Asymmetrical cyclic phosphite and phosphinite ligands of a novel type bearing either trifluoromethyl or pentafluorophenyl group were synthesized using >PCl or >PN< species and racemic fluorinated alcohols. The P-ligands were converted to complexes of Rh^III(L)(Cp^∗)Cl₂ type (where L = phosphite or phosphinite) and, in two instances, their stereostructures were evaluated by X-ray analysis. These complexes along with in situ systems, formed from Rh(CO)₂(acac) precursor and the corresponding ligand, were tested in the hydroformylation of styrene. Both systems provided excellent hydroformylation activities at 100 °C. Using the Rh^I in situ systems, moderate and high regioselectivities towards the branched aldehyde (2-phenyl-propanal) were obtained at 100 and 40 °C, respectively.     

A novel phosphate ligand used for the Rh-catalyzed hydroformylation of cyclohexene in a thermoregulated PEG biphase system

A novel phosphate ligand,tri-(methoxyl polyethylene glycol)-phosphate (TMPGPA),has been synthesized and used in the Rh- catalyzed hydroformylation of cyclohexene in a thermoregulated PEG biphase system.Under the optimized conditions, pressure=5 MPa (H_2:CO=1:1),P/Rh=10 (molar ratio),reaction time=4h and temperature=120℃,the conversion of cyciohexene and the yield of aldehyde are 99%.The catalyst retained in PEG phase can be easily separated from the organic phase containing product by simple phase separation and reused ten times without obvious loss in activity.     

Substrate-directed asymmetric induction in the rhodium catalyzed hydroformylation of C-allyl-sugars: The influence of the glycoside-moiety on the selectivity of the reaction

α- and β-C-allylgalactopyranosides 1c and 1d, α-C-allylazaglucopyranoside 1e and α-C-allylfruttofuranoside 1f were hydroformylated at low temperatures affording a mixture of linear and branched aldehydes in regioisomeric and diastereoisomeric ratios depending on the starting alkene. The results obtained have allowed us to study the influence of the different structural features of the sugar moiety on the regio- and diastereoselectivity of the hydroformylation reaction.     

Hydroformylation of alkenes with paraformaldehyde catalyzed by rhodium-phosphine complexes

The hydroformylation of medium-chain C6 olefins and of allyl alcohol was achieved with paraformaldehyde in dioxane solution using rhodium catalysts with mono-, bi-, and tri-dentate phosphine ligands. The highest activities with n/i ratios around 2, were obtained for a system derived from [Rh(dppe)₂]⁺, prepared in situ by reaction of Rh(acac)(CO)₂ with 2 eq of dppe.     

Ferrocene-based bidentate phosphonite ligands for rhodium(I)-catalyzed enantioselective hydroformylation

A new class of chiral modular bidentate phosphonite ligands has been synthesized in good overall yields by using cheap trans-1,2-diaminocyclohexane and ferrocene as starting materials, and applied in the Rh(I)-catalyzed asymmetric hydroformylation of vinyl acetate and styrene to afford the corresponding optically active aldehydes with good regioselectivity (up to 16.9 b/l ratio) and moderate to good enantioselectivity (up to 83% ee). The substituents on the backbone of the ligands are found to exhibit a remarkable effect on both the regio- and enantioselectivity of the catalysis.     

Highly regioselective hydroformylation of 1,5-hexadiene to linear dialdehyde catalyzed by rhodium complexes with tetraphosphorus ligands

Rhodium-catalyzed hydroformylation of 1,5-hexadiene to corresponding dialdehydes was investigated using tetraphosphorus ligands. These ligands showed a high regioselectivity for linear aldehydes (linear to branch ratio up to 98%) in very good yield (up to 87%). It was found that the introduction of the substituents at the ortho position of the biphenyl moiety has little effect on the regioselectivity and the electron-donating substituents retard the reaction somewhat.     

Synthesis, complexation behavior and application of a new diphosphite ligand in rhodium-catalyzed hydroformylation

Oxidative coupling of 3-(3-tert-butyl-4-hydroxyphenyl)propionic acid methyl ester (2) gave dimethyl 3,3′-(5,5′-di-tert-butyl-6,6′-dihydroxybiphenyl-3,3′-diyl)-dipropionate (1c), which upon phosphorylation/transesterification with a phosphochloridite derived from (R)-binaphthol, formed the new unsymmetrical binaphthol-bridged diphosphite 4. A rhodium catalyst based on 4 as ligand gave predominantly iso-selectivity in the hydroformylation of selected styrenes but opposite regioselectivity with 2,6-disubstituted derivatives. New chelate metal complexes (acac)RhL, PdCl₂L and PtCl₂L have been synthesized by reacting 4 with (acac)Rh(CO)₂, PdCl₂(MeCN)₂ and PtCl₂(COD), respectively. The structure of obtained compounds is determined based on ¹H, ¹³C, ³¹P and ¹⁹⁵Pt NMR spectroscopy and mass spectrometry data.     

Rhodium catalysed hydroformylation of unsaturated esters

Rhodium catalysed hydroformylation of unsaturated esters has been studied. A pronounced temperature dependence was observed on the regioselectivity and catalytic activity for these reactions, and under the appropriate conditions, it is possible to obtain preferentially either linear or quaternary products. A quaternary selective hydroformylation of methyl atropate to give 1,3-aldehydic esters has also been developed.     

Synthesis of 2-chromanol by hydroformylation of 2-hydroxystyrene derivatives

2-Benzyloxy- and 2-tosyloxystyrene were hydroformylated under different reaction conditions with the aim to obtain the corresponding linear aldehydes, valuable intermediates to 2-chromanol, a structural moiety present in several interesting therapeutically active molecules. The best results were obtained by using the catalytic precursor Pt(Xantphos)Cl₂ in toluene or the water-soluble catalytic system Rh(CO)₂acac/Xantphos(SO₃Na)₂ in the biphasic medium water/toluene. Rather good regioselectivities were also achieved employing the unmodified complex Rh₄(CO)₁₂ at high temperature and low pressure for very short reaction times: unfortunately the chemoselectivity of the process was not satisfactory, due to the extensive formation of the substrate hydrogenation product.     

HYDROFORMYLATION CATALYSIS USING POLYMER-SUPPORTED MULTINUCLEAR RHODIUM CARBONYL CLUSTER CATALYSTS

A series of polymer-supported tetranuclear rhodium carbonyl cluster catalysts were prepared b the reaction of Rh_4(CO)_(12) with several kinds of polymer supports such as crosslinked poly (N-vinylpyrrolidone) (PNVP) and crosslinked poly ( styrene-co-maleic anhydride) (PMAn), and subsequently were used to catalyze the hydroformylation of olefins. The catalysts were characterized by IR, SEM and XPS. The influence of the supports structure and crosslinking, metal's content and particle size of the supports on the catalysts hydroformylation properties was studied. The factors which affect the catalytic conversion were also examined. The experimental results show that the polymer-supported Rh cluster catalysts possess very high catalytic activity and aldehyde selectivity as well as good reproducibility.