Rhodium Diphosphine Complexes Research Articles

A Multicatalytic Approach to the Hydroaminomethylation of α-Olefins.

We report an approach to conducting the hydroaminomethylation of diverse α-olefins with a wide range of alkyl, aryl, and heteroarylamines at relatively low temperatures (70-80 °C) and pressures (1.0-3.4 bar) of synthesis gas. This approach is based on simultaneously using two distinct catalysts that are mutually compatible. The hydroformylation step is catalyzed by a rhodium diphosphine complex, and the reductive amination step, which is conducted as a transfer hydrogenation with aqueous, buffered sodium formate as the reducing agent, is catalyzed by a cyclometallated iridium complex. By adjusting the ratio of CO to H2 , we conducted the reaction at one atmosphere of gas with little change in yield. A diverse array of olefins and amines, including hetreroarylamines that do not react under more conventional conditions with a single catalyst, underwent hydroaminomethylation with this new system, and the pharmaceutical ibutilide was prepared in higher yield and under milder conditions than with a single catalyst.

A Multicatalytic Approach to the Hydroaminomethylation of α‐Olefins

AbstractWe report an approach to conducting the hydroaminomethylation of diverse α‐olefins with a wide range of alkyl, aryl, and heteroarylamines at relatively low temperatures (70–80 °C) and pressures (1.0–3.4 bar) of synthesis gas. This approach is based on simultaneously using two distinct catalysts that are mutually compatible. The hydroformylation step is catalyzed by a rhodium diphosphine complex, and the reductive amination step, which is conducted as a transfer hydrogenation with aqueous, buffered sodium formate as the reducing agent, is catalyzed by a cyclometallated iridium complex. By adjusting the ratio of CO to H2, we conducted the reaction at one atmosphere of gas with little change in yield. A diverse array of olefins and amines, including hetreroarylamines that do not react under more conventional conditions with a single catalyst, underwent hydroaminomethylation with this new system, and the pharmaceutical ibutilide was prepared in higher yield and under milder conditions than with a single catalyst.

13C NMR Signal Enhancement Using Parahydrogen-Induced Polarization Mediated by a Cobalt Hydrogenation Catalyst.

The use of a cobalt-based catalyst for the generation of hyperpolarized 13C NMR resonances by parahydrogenation of ethyl acrylate is presented herein. Comparisons of the carboxylate 13C NMR signal enhancement factor of ethyl propionate between using (MesCCC)Co-py and a commonly utilized cationic diphosphine rhodium complex demonstrates that the cobalt system is a viable PHIP catalyst alternative. Furthermore, the operative hydrogenation mechanism of the cobalt system was examined by using 1H, 13C, and parahydrogen-induced polarization NMR spectroscopies to elucidate reaction intermediates affiliated with the observed 1H and 13C NMR signal enhancements in ethyl propionate.

Oxidative addition of CH2Cl2 to neutral dimeric rhodium diphosphine complexes

Neutral dimeric rhodium diphosphine complexes are often employed as catalytic precursors in the presence of the solvent CH2Cl2. The possibility of a collateral reaction between the solvent and the catalytic precursor is never considered as the activation of CH2Cl2 by [Rh2(PP)2 (μ2-Cl)2] complexes is reputed difficult and uncommon. Herein we report the easy formation of three neutral dimeric Rh(III) complexes containing DPPP, DPPB and TangPhos through CH2Cl2 activation as an extension of the few examples reported so far. The system [Rh2 (DPPP)2 (μ2-Cl)2]/CH2Cl2 has been selected for a detailed mechanistic investigation. Kinetic studies based on 31P NMR monitoring combined with metathesis experiments reveal the fundamental role of a 14-electron intermediate [Rh(PP)Cl], which is involved in the CH2Cl2 activation.

Rh-Catalyzed Chemo- and Enantioselective Hydrogenation of Allylic Hydrazones.

A highly efficient P-stereogenic diphosphine-rhodium complex was applied to the chemo- and enantioselective hydrogenation of allylic hydrazones for the synthesis of chiral allylic hydrazines in 89-96 % yields and with 82-99 % ee values. This methodology was successfully applied to the preparation of versatile chiral allylic amine derivatives.

ChemInform Abstract: Asymmetric Hydrogenation of α‐Purine Nucleobase‐Substituted Acrylates with Rhodium Diphosphine Complexes: Access to Tenofovir Analogues.

AbstractVarious mono‐ and disubstituted acrylates are conveniently hydrogenated under very mild reaction conditions with good to excellent enantioselectivities.

Asymmetric Hydrogenation of α-Purine Nucleobase-Substituted Acrylates with Rhodium Diphosphine Complexes: Access to Tenofovir Analogues.

The first asymmetric hydrogenation of α-purine nucleobase-substituted α,β-unsaturated esters, catalyzed by a chiral rhodium (R)-Synphos catalyst, has been developed. A wide range of mono- and disubstituted acrylates were successfully hydrogenated under very mild conditions in high yields with good to excellent enantioselectivities (up to 99% ee). This method provides a convenient approach to the synthesis of a new kind of optically pure acyclic nucleoside and Tenofovir analogues.

X-ray photoelectron spectroscopy as a probe of rhodium-ligand interaction in ionic liquids

We use X-ray photoelectron spectroscopy (XPS) to identify the interaction between the rhodium atom and phosphine ligands in six 1-octyl-3-methylimidazolium-based ionic liquids ([C8C1Im][X]). The formation of a mono-phosphine rhodium complex based upon addition of triphenylphosphine (PPh3) is confirmed by XPS in all ionic liquids studied herein. Due to the electron donation effect of the ligand, the rhodium atom becomes more negatively charged and thus exhibits a lower measured binding energy. The influence of the anion basicity on the formation of different types of rhodium complexes is also investigated. By introducing a biphosphine ligand, a chelated diphosphine rhodium complex is formed in ionic liquids with more basic anions and verified by both XPS and Infrared Spectroscopy (IR). The measured Rh 3d binding energies are correlated to the reaction selectivity of a hydroformylation reaction which inspires a method to design a metal catalyst to control the chemical reaction towards desired products in the future.

In Situ Synthesis of Neutral Dinuclear Rhodium Diphosphine Complexes [{Rh(diphosphine)(μ2‐X)}2]: Systematic Investigations

AbstractAs the workhorses for many applications, neutral dimeric μ2‐X‐bridged diphosphine rhodium complexes of the type [{Rh(diphosphine)(μ2‐X)}2] (X=Cl, OH) are usually prepared in situ by the addition of diphosphine ligands to the rhodium complex [{Rh(diolefin)(μ2‐X)}2] (diolefin=cyclooctadiene (cod) or norbornadiene (nbd)) or [{Rh(monoolefin)2(μ2‐Cl)}2] (monoolefin=cyclooctene (coe) or ethylene (C2H4)). The in situ procedure has been investigated for the diphosphines 2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl (BINAP), 5,5′‐bis(diphenylphosphino)‐4,4′‐bi‐1,3‐benzodioxole (SEGPHOS), 5,5′‐bis[di(3,5‐xylyl)phosphino]‐4,4′‐bi‐1,3‐benzodioxole (DM‐SEGPHOS), 5,5′‐bis[di(3,5‐di‐tert‐butyl‐4‐methoxyphenyl)phosphino]‐4,4′‐bi‐1,3‐benzodioxole (DTBM‐SEGPHOS), 2,2′‐bis(diphenylphosphino)‐1,1′‐dicyclopentane (BICP), 1‐[2‐(diphenylphosphino)ferrocenyl]ethyldi‐tert‐butylphosphine (PPF‐PtBu2), 1,1′‐bis(diisopropylphosphino)ferrocene (DiPPF), 1,2‐bis(diphenylphosphino)ethane (DPPE), 1,2‐bis(o‐methoxyphenylphosphino)ethane (DIPAMP), 4,5‐bis(diphenylphosphinomethyl)‐2,2‐dimethyl‐1,3‐dioxalane (DIOP), 1,2‐bis(2,5‐dimethylphospholano)benzene (Me‐DuPHOS), 1,4‐bis(diphenylphosphino)butane (DPPB), and 1,3‐bis(diphenylphosphino)propane (DPPP); the resulting complexes have been characterized by 31P NMR spectroscopy and, in most cases, also by X‐ray analysis. Depending on the diphosphine ligand, the solvent, the temperature, and the rhodium precursor, species other than the desired one [{Rh(diphosphine)(μ2‐X)}2] are formed, for example, [(diolefin)Rh(μ2‐Cl)2Rh(diphosphine)], [Rh(diphosphine)(diolefin)]+, [Rh(diphosphine)2]+, and [Rh(diphosphine)(diolefin)(Cl)]. The results clearly show that the in situ method commonly applied for precatalyst preparation cannot be regarded as an optimal strategy for the formation of such neutral [{Rh(diphosphine)(μ2‐X)}2] complexes.

Rhodium diphosphine complexes: a case study for catalyst activation and deactivation

The present work provides an overview of possible activation and deactivation phenomena in homogeneous catalytic processes promoted by different types of rhodium complexes containing diphosphine ligands.

Cationic Rhodium-BINAP Complexes: Full Characterization of Solvate- and Arene-Bridged Dimeric Species

In the asymmetric hydrogenation promoted by rhodium-diphosphine complexes in coordinating solvents such as methanol, the solvate complex is regarded as the catalytically active species. Here, we pr...

Synthesis of hybrid transition-metalloproteins via thiol-selective covalent anchoring of Rh-phosphine and Ru-phenanthroline complexes

The preparation of hybrid transition metalloproteins by thiol-selective incorporation of organometallic rhodium- and ruthenium complexes is described. Phosphine ligands and two rhodium-diphosphine complexes bearing a carboxylic acid group were coupled to the cysteine of PYP R52G, yielding a metalloenzyme active in the rhodium catalyzed hydrogenation of dimethyl itaconate. The successful coupling was shown by (31)P NMR spectroscopy and ESI mass spectroscopy. In addition wild-type PYP (PYP WT), PYP R52G and ALBP were successfully modified with a (eta(6)-arene) ruthenium(II) phenanthroline complex via a maleimide linker.

Ordered mesoporous materials as solid supports for rhodium–diphosphine catalysts with remarkable hydroformylation activity

A rhodium-diphosphine complex based on Xantphos-type ligands was anchored on mesoporous silica SBA-15, and the material showed remarkably high catalytic activity in the hydroformylation of 1-octene, even exceeding its homogeneous analogue under certain conditions.

Kinetic and mechanistic investigations in homogeneous catalysis using operando UV/vis spectroscopy

This study presents three examples in which the methodological approach of operando UV/vis spectroscopy is demonstrated using both submersible optrodes and the stopped flow/diode array technique. First, the submersible optrode is applied for the monitoring of stoichiometric reactions, that is the hydrogenation of cyclooctadiene (cod) in the rhodium diphosphine complex [Rh(Me-Du-PHOS)(cod)]BF 4 (Me-DuPHOS = 1,2-bis(-2,5-dimethyl-phospholano)benzene), which is a typical catalyst precursor in asymmetric hydrogenation. Second, the determination of stability constants for rhodium diphosphine arene complexes is shown. The third example presents UV/vis spectroscopy of zirconium and hafnium complexes with ethylene as a gaseous reaction partner using the stopped flow/diode array technique.

Immobilization of chiral cationic diphosphine rhodium complexes in nanopores of mesoporous silica and application in asymmetric hydrogenation

Heterogeneous chiral cationic rhodium complexes bearing bidentate phosphine derived from (−)-2,2-dimethyl-4,5-bis(diphenylphosphino)methyl)-1,3-dioxolane (DIOP) were prepared by covalent immobilization onto SBA type silica. In order to introduce the tether to the surface, it was necessary to modify chemically the DIOP ligand through a reaction sequence consisting of hydrolysis and condensation with organosiloxane precursor. Two types of cationic rhodium hybrid materials based on SBA-15 and partially capped SBA-3 type silica were prepared under classical grafting procedures. The catalytic solids were fully characterized using a wide variety of molecular and solid-state techniques to determine their structural and textural properties. The performances of these latter were then evaluated in the hydrogenation of methyl ( Z)-2- N-acetylaminocinnamate under various reaction conditions (pressure and temperature). Generally, the activity of supported catalysts was high as full conversions were obtained but immobilization of the system leads to significant loss of enantioselectivity. The best ee (20%) was observed in the case of the catalyst whose surface had been passivated prior to the grafting but the enantiomeric excesses were fairly below the values of the homogeneous catalysis.

Heterogeneously catalyzed asymmetric hydrogenation of α-arylenamides over immobilized RhBPE and RhDUPHOS complexes

Optically active α-1-arylalkylamine derivatives were successfully synthesized through heterogeneous asymmetric hydrogenation of α-arylenamides over immobilized RhBPE and RhDUPHOS complexes on aluminum-containing M41S and SBA-15 type materials. The heterogeneous chiral catalysts were prepared by immobilization of rhodium diphosphine complexes on Al-MCM-41, Al-MCM-48, and Al-SBA-15. The complexes were bonded to the carrier by the interaction of the cationic rhodium of the organometallic complex with the anionic host framework, as well as between Al Lewis acid sites and P Lewis basic sites. The catalysts were characterized with XRD, FT-IR and MAS-NMR, as well as thermoprogramed desorption of ammonia, thermogravimetric analysis, and nitrogen sorption experiments. The immobilized catalysts showed high activities and excellent chemo- and enantioselectivities. Up to 99% e.e. at 99% conversion and >99% chemoselectivity were observed in the case of studied α-arylenamides. The catalysts could be reused up to four times without loss of catalytic activity or enantioselectivity.

Asymmetric Hydrogenation Approaches to Valuable, Acyclic 1,3-Hydroxymethyl Chirons

An iridium carbene oxazoline complex was used to catalyze hydrogenations of trisubstituted alkenes to give terminal and internal 1,3-hydroxymethyl chirons. The products are accessible in all possible stereoisomeric forms. These hydrogenations do not require strongly coordinating functionalities on the substrate, and in some key cases, catalyst- rather than substrate-controlled stereoselectivities are observed. It is hypothesized that these reactions would not be feasible using iridium or rhodium diphosphine complexes.

Wide bite angle diphosphine rhodium complexes: Synthesis, structure, and catalytic 1,4-addition of arylboronic acids to enones

A rhodium complex [ClRh(CO)( L1)] featuring a wide bite angle diphosphine ligand ( L1 = 1,3-bis(2-diphenylphosphinomethylphenyl)benzene) has been synthesized and structurally characterized. L1 supports a bite angle (P–M–P angle, β) of 171.4° in the trans-square planar complex. L1 was tested in Rh-catalyzed 1,4-addition reactions of arylboronic acids (six examples) to α,β-unsaturated ketones (five examples). In mixed aqueous/cyclohexane solution at 60 °C, addition reactions proceed in up to quantitative yield with a 1:1 arylboronic acid/enone ratio. Yields as high as 77% can be acquired even when one of the coupling partners is sterically encumbered 2,4,6-trimethylphenylboronic acid.

Counter propagation artificial neural networks modeling of an enantioselectivity of artificial metalloenzymes

The counter propagation artificial neural networks (CP-ANNs) were used to develop a quantitative structure-selectivity relationship (QSSR) for a set of artificial metalloenzymes. The artificial metalloenzymes consist of biotinylated rhodium-diphosphine complexes incorporated in streptavidin mutants acting as host protein. Such hybrid catalysts have been shown to be good enantioselective hydrogenation catalysts for acetamidoacrylic acid. The descriptor-based models were constructed to predict enantiomeric excess (%ee) on the basis of the catalyst structures originating from docking simulations. 3D molecular descriptors for the docked ligands structures were computed. The relative arrangement of guest and host molecules was coded using distance descriptors (Rh-C(alpha) interatomic distances); the diversity of the mutant proteins at the position S112 was coded with molecular descriptors for the sequence of three neighboring amino acids (T111-S112X-G113). The selection of testing samples for the external model validation was based on the Kohonen mapping. The final model trained by two thirds of the entire dataset was characterized by satisfactory statistical parameters for the external test set (R = 0.953 and RMS = 16.8 %ee). The proposed procedure of docking-based descriptor generation thus appears as a promising alternative to the full characterization of the complex structure by experimental or computational methods.

Enantioselective hydrogenation over immobilized rhodium diphosphine complexes on mesostructured materials

New heterogeneous chiral catalysts were prepared from rhodium diphosphine complexes [Rh(P–P)COD]Cl ((P–P) = diphosphine ligand and COD = cyclooctadiene), and Al–MCM-41, Al–MCM-48, and Al–SBA-15, respectively. Impregnation of the mesoporous Al–MCM-41, Al–MCM-48, and Al–SBA-15 with the organometallic complexes in dichloromethane led to strongly bonded hydrogenation catalysts. The catalysts were characterised with XRD, FT-IR and MAS-NMR, as well as thermoprogrammed desorption of ammonia, thermogravimetric analysis, and nitrogen sorption experiments. The hydrogenation of dimethyl itaconate, methyl α-acetamidoacrylate, and methyl α-acetamidocinnamate were studied as test reactions. The immobilized catalysts showed high activities and excellent chemo- and enantioselectivities. Up to 98% e.e., >99% conversion and 99% selectivity were observed in the case of studied prochiral olefins. The catalysts could be reused without a loss of catalytic activity. Leaching of the homogeneous complex out of the mesoporous framework was not observed.