Rh Complex Catalyst Research Articles

Mechanochemical-induced cis-to- trans isomerization of poly(2-ethynyl-3- n-octylthiophene) prepared with a Rh complex catalyst

Highly stereoregular polymerization of 2-ethynyl-3- n-octylthiophene was successfully performed with a [Rh(norbornadiene)Cl] 2 catalyst to produce the corresponding polymers in fairly high yields by using triethylamine or a mixture of it with other solvents as the polymerization solvent. We found that the obtained polymer using CHCl 3 was a mixture of cis-transoid form, ca. 68% and trans-transoid form, ca. 32% unlike our previous conjecture. Further, we found that the cis-to- trans isomerization can be also induced when the pristine predominant cis polymer was subjected to mechanochemical grinding (MCG) treatment at 77 K using a mortar filled with liquid nitrogen to decrease the cis content from ca. 68% to ca. 7%. The polymers obtained before and after the MCG treatment were characterized in detail using 1H NMR, laser Raman, solution UV–vis, diffuse reflective UV–vis, and ESR methods in order to determine the geometry of the main-chain C C bonds in the polymer. The data showed that the polymer obtained by the treatment has a fairly distorted trans conjugation length, i.e., bent trans structure in which less mobile unpaired electrons generated by the rotational scission of the original cis C C bonds are stabilized.

Transition-Metal Complexes with Nano-Sized Phosphine and Pyridine Ligands-Catalysis, Fluxional Behavior and Molecular Recognition

Nano-sized phosphine and pyridine ligands having tetraphenylphenyl-, m-terphenyl-, poly(benzylether) moieties were synthesized. These ligands showed a remarkable effect on homogeneous transition metal catalyzed reactions. Pd(II) complexes with tetraphenylphenyl substituted pyridine ligands show high catalytic activities for oxidation of ketones suppressing Pd black formation and maintains the catalytic activity for a long time. Rh(I) complex catalysts with m-terphenyl substituted phosphine ligands showed remarkable rate acceleration in the hydrosilylation of ketones. In addition, several phosphinocalixarene ligands were synthesized and their coordination studies with Pd(II), Pt(II), Ru(II), Ir(I), and Rh(I) metals were documented. Ir(I) and Rh(I) cationic complexes with a 1,3,5-triphosphinocalix[6]arene ligand showed dynamic behavior with size-selective molecular recognition.

Evidence of colloidal rhodium formation during the biphasic hydroformylation of 1-octene with thermoregulated phase-transfer phosphine rhodium(I) catalyst

A thermoregulated phase-transfer (TRPT) Rh(I) complex catalyst A prepared from Rh(acac)(CO)2 and a thermoregulated ligand CH3(OCH2CH2)mPPh2 (Mw = 918) was applied to the biphasic hydroformylation of 1-octene, and a high activity with an aldehyde yield of 97.5% was demonstrated. After three recycling steps, the aldehyde yield gradually decreased. Transmission electron microscopy (TEM) revealed that after the first cycle Rh colloids were generated in situ in the aqueous phase, and in subsequent runs Ostwald ripening occurred. An independently prepared colloidal Rh(0) TRPT catalyst D also exhibited high hydroformylation activity under identical experimental conditions, and after two times of recycling an activity decrease was also observed. It is suggested that in situ from Rh(acac)(CO)2 colloidal Rh particles are generated, which demonstrate thermomorphic behaviour and a high hydroformylation activity. Subsequently, agglomeration processes result in an activity decay, as observed in the TRPT Rh(I) complex catalyst system. Copyright © 2005 John Wiley & Sons, Ltd.

Ammonium Salts with Polyether-Tail: New Ionic Liquids for Rhodium Catalyzed Two-Phase Hydroformylation of 1-Tetradecene

By attaching the polyether chains to ammonium salts, a novel class of ionic liquid termed polyether melt is prepared. Such polyether melt contains no fluoride and hence is environmentally more benign. Applying this polyether melt as a polar phase, the hydroformylation of 1-tetradecene catalyzed by Rh complex catalyst in two-phase medium was investigated. The rhodium catalyst immobilized in this polyether melt is readily separated from the aldehyde product phase by decantation and has been reused for seven times without obvious loss of activity.

Spin Glass‐like Behavior of Poly(phenylacetylene) Prepared with a Rh Complex Catalyst, 1

AbstractSummary: Magnetic field dependence of poly(phenylacetylene) (PPA) that has been stereoregularly prepared with a Rh complex catalyst was investigated in detail between 2 K and 300 K. The data showed a spin glass‐like magnetic behavior, i.e., two cusps were clearly observed when PPA was zero‐field‐cooled together with slow increasing of the magnetization (called an ageing effect) at 45 K. The observed spin glass‐like behavior has been discussed in terms of an ageing effect, which may have been caused by weak anti‐ferromagnetic interactions between intra‐ and/or inter‐magnetic spins produced by cis‐to‐trans isomerization through the rotational scission of the cis CC bond of the PPA polymer during polymerization.Intra‐molecular anti‐ferromagnetic interactions.magnified imageIntra‐molecular anti‐ferromagnetic interactions.

Pressure‐Induced cis‐to‐trans Isomerization of Poly[(p‐methylthiophenyl)acetylene] Prepared with a [Rh(norbornadiene)Cl]2 Catalyst – A Raman, UV‐Vis, and ESR Study

AbstractSummary: A stereospecific polymerization of a novel aromatic acetylene containing an alkyl sulfide group, i.e., (p‐methylthiophenyl)acetylene (pMeSPA) was successfully performed to selectively give the corresponding polymer bearing a cis‐transoid structure as a main geometrical form and a very high molecular weight, $\overline M _{\rm n}$ = 1.7–5.8 × 106 in high yields. This was accomplished when a Rh complex catalyst, [Rh(norbornadiene)Cl]2, was used in the presence of triethylamine (TEA) solvent as a cocatalyst and its mixed solvents with TEA, together with a detailed characterization of the resulting polymers before and after compression at room temperature. Based on the data obtained before and after compression, it was concluded that compression of the PpMeSPA polymers induced a cis‐to‐trans isomerization at room temperature under vacuum even in the solid state (the Figure shows the radical generated by compression). magnified image

Encapsulated HRh(CO)(PPh3)3 in Microporous and Mesoporous Supports: Novel Heterogeneous Catalysts for Hydroformylation

Novel heterogeneous catalysts for hydroformylation of olefins to aldehydes using encapsulation and anchoring methodologies for HRh(CO)(PPh 3 ) 3 in zeolite Na-Y and MCM-41 and MCM-48 mesoporous materials have been reported. The heterogeneous catalysts were characterized and used for hydroformylation of linear and branched olefins to show high activity and recyclability without leaching of the Rh metal during the course of reactions. Using CP-MAS NMR, FT-IR, TEM, XPS, and powder XRD studies, characterization of the Rh complex inside the porous structures of the heterogeneous catalysts has been investigated. 31 P CP-MAS NMR spectra of the encapsulated Rh complex catalyst inside zeolite Na-Y and mesoporous MCM-41 and MCM-48 supports showed a possible encapsulation of the Rh complex in the pores. TEM images and the diffraction patterns of the heterogenized Rh complex in mesoporous and zeolitic supports further supported a possible entrapment of the complex inside the porous frameworks. Rhodium is present as Rh(I) in the encapsulated catalysts before and after the experiments, as envisaged by XPS spectra. In contrast to other heterogeneous catalytic systems for hydroformylation, the catalysts reported here are highly stable, easily separable, and recyclable. The TON/TOF values of these catalysts were also found to be significantly higher than those of the previously reported heterogeneous catalysts.

Activity and selectivity of Rh-complex catalysts in hydroformylation of 1,4-diacetoxy-butene to Vitamin A intermediate

Hydroformylation of 1,4-diacetoxy-butene using homogeneous HRh(CO)(PPh 3) 3 catalyst was investigated with the aim to understand product distribution, selectivity and intrinsic kinetics. The effect of HRh(CO)(PPh 3) 3 and 1,4-diacetoxy-2-butene (DAB) concentrations, and CO and H 2 partial pressures on the concentration versus time profiles was studied over a temperature range of 338–358 K. The activity and selectivity of a tethered Rh-complex catalyst on Na-Y zeolite support and a water-soluble Rh-TPPTS catalyst in a two-phase system were also studied and the performance was compared with the homogeneous catalyst. It was observed that both the tethered and biphasic catalysts were highly stable during recycle, though the activity of these catalysts was lower than the homogeneous catalyst. Rate equations have been proposed for both the hydroformylation and deacetoxylation steps. The activation energies were found to be 75.24 and 108.9 kJ/mol, respectively.

Asymmetric hydrogenation of diketones catalyzed by magnesium oxide‐supported chitosan–Rh complex

AbstractMgO‐supported chitosan–Rh complex (MgO‐CS‐Rh) has been prepared and found to be a highly stereoselective catalyst for the asymmetric hydrogenation of some diketones to corresponding chiral alcohols, such as 2,3‐butanedione to (2S,3S)‐(+)‐2,3‐butanediol and 2,4‐pentanedione to (2S,4S)‐(+)‐2,4‐pentanediol at room temperature and under 1 atm H2. The optical yield was greatly affected by the Rh content in the complex, the solvent and the reaction temperature. The optical yields of (2S,3S)‐(+)‐2,3‐butanediol and (3S,4S)‐(+)‐2,4‐pentanediol obtained were 87% and 81.2%, respectively. The chiral chitosan–Rh complex catalyst was very easy to prepare, and could be reused without noticeable change in its optical catalytic activity. Copyright © 2003 John Wiley & Sons, Ltd.

Theoretical Investigation on Functionalization of Alkanes by a Rhodium Complex Catalyst

A theoretical study has been carried out for the detailed mechanism of Rh-catalyzed alkane borylation reaction with the density functional methods of B3LYP and B3PW91 and the MP2 methods. The pathway of the reaction has been shown to proceed via two steps: (a) formation of the reactive boryl intermediate; (b) C−H bond activation and B−C bond formation. Although the geometries and energetics derived from the three methods differ dramatically, they give a consistent prediction of the preference of the oxidative addition and reductive elimination pathway for the alkane functionalization by the Rh-complex catalyst.

Photoinduced Cis-to-Trans Isomerization of Poly(2-ethynylthiophene) Prepared with a [Rh(norbornadiene)Cl]2 Catalyst. 1H NMR, UV, and ESR Studies

Poly(2-ethynylthiophene) was stereoregularly prepared with a Rh complex catalyst, [Rh(norbornadiene)Cl]2, to selectively produce the cis−transoid isomer in high yields when triethylamine was used as the polymerization solvent at 20 °C. Photoinduced cis-to-trans isomerization was newly found to take place when the film of a pristine cis−transoid polymer was photoilluminated using a Xe lamp with light of wavelength, 320−500 nm under vacuum for 5 h. The cis and trans polymers obtained before and after the illumination were characterized in detail using 1H NMR, UV−vis of solution and film, and electron spin resonance methods.

Rhodium(I) complex catalysts immobilized on polyamides having a pyridine moiety: Effect of the polymer structure

A series of polyamides have been synthesized by low-temperature interfacial condensation of 2,5- and 2,6-pyridinedicarboxylic chlorides and aliphatic diamines H 2N(CH 2) n NH, where n=2 and 6, and used as the model supports for immobilization of the Rh(I) complex catalyst. Physical characterization of these materials has involved the measurements of the structural parameters in the dry and swollen states by WAXS, SAXS, DSC, the nitrogen BET adsorption method, ISEC and pycnometry. From these results it can be concluded that the original polymer structure has been changed during the complex attachment giving rise to materials of higher porosity. The relation between the support structure and catalyst activity and selectivity was studied in the model reactions, namely, hydrosilylation of alkenes, dienes and alkynes. It was found that the catalyst activity decreased with increasing polymer crystallinity. A strong impact of support structure on the catalyst selectivity was also revealed. A high regioselectivity of the catalyst in the hydrosilylation of alkenes toward formation of the linear products was achieved due to the favorable microporous structure of the polyamide supports with pore sizes between 10 and 20 Å. It was also demonstrated that the stereoselectivity of the reaction can be reversed to the opposite direction by a proper choice of the donor functions in a polymer support, e.g. the traditional cis-selectivity of the rhodium (Rh) catalysts in the hydrosilylation of phenylacetylene was changed to trans-selectivity by use of the 2,5-py instead of 2,6-py moiety. The results of the 6–9 times repeated catalytic runs indicated high stability of the polyamide-supported catalysts.

Hydrogenation of Arenes under Mild Conditions Using Rhodium Pyridylphosphine and Bipyridyl Complexes Tethered to a Silica-Supported Palladium Heterogeneous Catalyst

The rhodium complexes [Rh(COD)(1)]BF4 (Rh(N−P)) and [Rh(COD)(2)]BF4 (Rh(N−N)), containing the new pyridylphosphine and bipyridyl ligands (1 and 2) with alkoxysilane groups, were tethered on the silica-supported palladium heterogeneous catalyst Pd−SiO2 to give the TCSM (tethered complex on supported metal) catalysts Rh(N−P)/Pd−SiO2 and Rh(N−N)/Pd−SiO2. Under the mild conditions of 70 °C and 4 atm of H2, the two TCSM catalysts are very active for the hydrogenation of arenes (PhCO2Me, PhOH, toluene, PhOCH3, PhCO2Et, 4-CH3C6H4CO2Et, dimethyl terephthalate) to cyclohexanes; the activities are higher than those of the separate homogeneous Rh(N−P) and Rh(N−N) complex catalysts, the silica-supported palladium catalyst Pd−SiO2, or the rhodium complex catalysts tethered on just SiO2. The catalysts are easily separated from the reaction mixtures and can be recycled several times without losing activity. Of the two TCSM catalysts, the higher activity for the hydrogenation of anisole to methyl cyclohexyl ether was observed for Rh(N−N)/Pd−SiO2, which gives a TOF value of 3060 mol of substrate converted/((mol of Rh) h) and a TO value of 14 500 mol of substrate converted/(mol of Rh) in 6 h. Reactions of acetophenone lead to hydrogenation of the arene ring, the carbonyl group, or both, depending on the catalyst (Rh(N−P)/Pd−SiO2 or Rh(N−N)/Pd−SiO2) and the solvent (heptane or ethanol).

Precise synthesis of monosubstituted polyacetylenes using Rh complex catalysts. Control of solid structure and π-conjugation length

Stereospecific polymerization of monosubstituted acetylenes was successfully performed using a Rh complex, [Rh(norbornadiene)Cl] 2 , as a catalyst, and the resulting polyacetylenes were characterized in detail by 1 H NMR, ESR, laser Raman, diffuse reflective UV, and wide-angle X-ray diffraction. The Rh complex was found to yield selectively the cis-transoid isomer even at room temperature in high yields when alcohol or triethylamine was used as the solvent. Additionally, the resulting cis-polyacetylenes were found to form a pseudohexagonal, columnar self-assembly or superstructure. Further compression of the cis-polymers induced cis-trans isomerization even at room temperature under vacuum, breaking rotationally the cis-C=C bonds and, thus, giving π-radicals as the origin of magnetic properties.

Homogeneous hydrogenation of maleic anhydride to succinic anhydride catalyzed by Rh complex catalyst

Hydrogenation of maleic anhydride using various homogeneous transition metal complex catalyst system has been investigated. It was observed that RhCl(PPh 3) 3 was the most active catalyst precursor for the hydrogenation of maleic anhydride to succinic anhydride. The optimum ligand and solvent were PPh 3 and ethylene glycol dimethylether, respectively. The effects of PPh 3:Rh mole ratio, temperature and pressure of H 2 have been studied. The typical experimental conditions are: temperature, 353–383 K; pressure of H 2, 0.5–2.5 MPa; PPh 3:RhCl(PPh 3) 3, 0–16; RhCl(PPh 3) 3, 0.03 mmol; maleic anhydride, 20 mmol; volume of liquid, 8 ml; reaction time, 30–360 min. Under these experimental conditions, succinic anhydride was the only product, and the highest yield (99.0%) was obtained. A reasonable reaction mechanism is proposed.

Photoswitching Properties of Polyacetylene Derivatives with a Photoinduced Azobenzene Moiety in the Side Group

We report on the photoswitching properties of novel mono-substituted polyacetylene derivatives with various azobenzene moieties that are photochemically reactive in the side group. Polymerization of the polyacetylene derivatives were carried out with Ziegler-Natta, metathesis, and Rh complex catalysts. When exposed with 350 nm UV or 450 run visible monochromatic light, the azobenzene side groups in the polyacetylene derivatives undergo trans ↔ cis reversible photoisomerization process. The photoisomerization rate of polyacetylene derivatives having a long alkyl chain in the azobenzene terminal group was more effective due to the providing of enough intermolecular free volume.

Pressure-inducedcis totrans isomerization of aromatic polyacetylenes prepared using a Rh complex catalyst: A control of ?-conjugation length

This study reports that stereospecific polymerization of aromatic acetylenes, e.g., p-methoxyphenylacetylene (pMOPA) and p-ethoxyphenylacetylene (pEOPA)was successfully performed to give polyacetylene selectively bearing cis-transoid forms in high yield when a Rh complex catalyst, [Rh(norbornadiene)Cl]2 was used in the presence of triethylamine as the polymerization solvent together with a detailed characterization of the resulting polymers, before and after compression. Compression of these polymers induced a cis-trans isomerization at room temperature under vacuum even in the solid state. Based on data collected before and after compression it is estimated that the trans conjugated length, (CC)n, produced as a result of the compression is n = 26 for PpMOPA and n = 40 for PpEOPA polymers, respectively. We further found that g values in the ESR spectra of the pristine polymer were shifted to higher magnetic field by compression, indicating that unpaired electrons called solitons are stabilized in the trans conjugation length as mobile electrons, although in the pristine polymers the unpaired electrons are stabilized in the less conjugated chain, showing large g value, suggesting a magnetic interaction between oxygen in the alkoxy group of phenyl moiety and unpaired electrons in the cis form. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 217–223, 1998

精密重合・精密合成高分子 ＩＩ Ｒｈ錯体触媒によるカラムナー構造を有するポリアセチレンの合成

精密重合・精密合成高分子 ＩＩ Ｒｈ錯体触媒によるカラムナー構造を有するポリアセチレンの合成

Asymmetric hydrogenation of α,β-unsaturated carboxylic acid esters by rhodium(I) — phosphine complexes supported on smectites

Hectorite(HT)-supported Rh complex catalysts were prepared by the interaction of [Rh(P ∗−P ∗)(COD)] + (P ∗−P ∗ = ( S)-BINAP and ( S)-( R)-BPPFA, COD - cyclooctadiene) into sodium hectorites (NaHT) in acetonitrile/H 2O. The basal spacing of each modified clay was 2.94 nm (BINAP) and 2.72 nm (BPPFA), respectively. Asymmetric hydrogenation of α,β-unsaturated carboxylic acid esters containing ester groups of various chain lengths was studied on these modified hectorites. The dependence of selectivity on employed solvents and bulkiness of the ester groups suggested that the interaction between substrates and the active sites increased in the interlayer space, thus enhancing the asymmetric selectivity.

Structural Differences between Polypentynoates Bearing Mesogenic Moieties Polymerized with RH Complex and WCl6Catalysts. A13C-NMR and Raman Study

Abstract Pentynoates containing mesogenic groups, i.e., HC[dbnd]CCH2CH2-COOR (R = dihydrocholesteryl and p-methoxybiphenyl) were stereoregularly polymerized using a Rh complex catalyst, [Rh(norbornadiene)Cl]2, in the presence of triethylamine as the cocatalyst. The structure of the polymer obtained was compared with that of an analogous polymer prepared using the metathesis catalyst WCI6 in dioxane by 13C-NMR and laser Raman spectroscopic methods. The data indicated that the polypentynoate polymerized with the Rh complex has a cis-transoid form which allowed us to observe the two clear carbon signals C[dbnd]CH of the main chain in the 13C-NMR spectrum. The polypentynoate prepared using the WCI6 catalyst was found to have the trans-transoid conjugation length with N c[dbnd]c ≉ 7, which did not allow observation of the clear carbon signals of the main chain in the 13C-NMR spectrum.