Ruthenium Phosphine Research Articles

Synthesis and dehydrocoupling reactivity of iron and ruthenium phosphine–borane complexes

The Fe and Ru phosphine-borane complexes CpM(CO)2PPh2 x BH3 (1, M = Fe, 4, M = Ru) were synthesized utilizing the reaction of the phosphine-borane anion Li[PPh2 x BH3] with the iodo complexes CpM(CO)2I. The Fe complex 1 reacted with PMe3 to yield CpFe(CO)(PMe3)(PPh2 x BH3) (2) and CpFe(PMe3)2(PPh2 x BH3) (3) whereas the Ru species 4 gave only CpRu(CO)(PMe3)(PPh2 x BH3) (5). The complexes 1-5 were characterized by 1H, 11B, 13C and 31P NMR spectroscopy, MS, IR and X-ray crystallography for 1 to 4, and EA for 1, 2 and 4. The reactivity of 1 and 4 towards PPh2H x BH3 was explored. Although no stoichiometric reactions were detected under mild conditions, both 1 and 4 were found to function as dehydrocoupling catalysts to afford Ph2PH x BH2 x PPh2 x BH3 in the melt at elevated temperature (120 degrees C). The carbonyl Fe2(CO)9 also functioned as a dehydrocoupling catalyst under similar conditions. Complex 1 and Fe2(CO)9 represent the first reported active Fe complexes for the catalytic dehydrocoupling of phosphine-borane adducts.

N‐Heterocyclic Carbene and Phosphine Ruthenium Indenylidene Precatalysts: A Comparative Study in Olefin Metathesis

Kinetic studies on ring-closing metathesis of unhindered and hindered substrates using phosphine and N-heterocyclic carbene (NHC)-containing ruthenium-indenylidene complexes (first and second generation precatalysts, respectively) have been carried out. These studies reveal an appealing difference, between the phosphine and NHC-containing catalysts, associated with a distinctive rate-determining step in the reaction mechanism. These catalysts have been compared with the benzylidene generation catalysts and their respective representative substrates. Finally, the reaction scope of the two most interesting precatalysts, complexes that contain tricyclohexylphosphine and 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (SIMes), has been investigated for the ring-closing and enyne metathesis for a large range of olefins. Owing to their high thermal stability, the SIMes-based indenylidene complexes were more efficient than their benzylidene analogues in the ring-closing metathesis of tetrasubstituted dienes. Importantly, none of the indenylidene precatalysts were found to be the most efficient for all of the substrates, indeed, a complementary complex-to-substrate activity relationship was observed.

X-ray structure, redox and spectroscopic properties of ruthenium phosphine complexes [Ru(tpy)(bpy)(PPh 3)] 2+ and [Ru(tpy)(bpy)(PCy 3)] 2+

The synthesis and crystal structures of two new phosphine ruthenium polypyridine complexes [Ru(tpy)(bpy)(PR 3)] 2+ with R = Ph ( 1), Cy ( 2) are reported. Their geometrical parameters are intimately related to the electronic and steric properties of the phosphine ligand. Electrochemical and UV–Vis analyses showed the influence of the substituents of the coordinated phosphorus atom on the Ru III/Ru II potential and on the frontier orbitals energy gap. The results are discussed in terms of steric effects and net donor power of the phosphine ligands.

Efficient transfer hydrogenation of ketones in the presence of ruthenium N-heterocyclic carbene catalysts

Novel ruthenium carbene complexes have been in situ generated and tested for the transfer hydrogenation of ketones. Applying Ru(cod)(methylallyl) 2 in the presence of imidazolium salts in 2-propanol and sodium-2-propanolate as base, turnover frequencies up to 346 h −1 have been obtained for reduction of acetophenone. A comparative study involving ruthenium carbene and ruthenium phosphine complexes demonstrated the higher activity of ruthenium carbene complexes.

Reactions of small boranes with ruthenium phosphine hydrides: Oligomerisation of monoborane-tetrahydrofuran to a nido-hexaruthenaborane

Reaction of [Ru(PPh 3) 4H 2] with BH 3 · thf at room temperature gives borane oligomerisation with the formation of the 6-vertex metallaborane nido-2-[Ru(PPh 3) 2(H)B 5H 10] ( 1). This cluster is also formed by reaction of [Ru(PPh 3) 4H 2] with nido-B 5H 9. Compound ( 1) is readily deprotonated by KH in thf at the unique basal B–H–B bridge to give nido - 2 - [ Ru ( PPh 3 ) 2 ( H ) B 5 H 9 - ] [ K + ] ( 2). In contrast to [Ru(PPh 3) 4H 2] reaction of [ cis-Ru(PMe 3) 4H 2] with BH 3 · thf gives initially the known borohydride [Ru(PMe 3) 3(H)(η 2-BH 4)] which reacts with excess BH 3 · thf to give the 5-vertex metallaborane nido-2-[Ru(PMe 3) 3B 4H 8] ( 3). Reaction of [ cis-Ru(PMe 3) 4H 2] with nido-B 5H 9 also gives ( 3) and nido-2-[Ru(PMe 3) 3B 9H 13] ( 4). [ cis-Ru(PMe 3) 4H 2] is conveniently prepared in high yield in a one-pot synthesis by the sodium amalgam reduction of RuCl 3 · 3H 2O in thf with excess PMe 3 under dinitrogen.

Recyclability of water-soluble ruthenium–phosphine complex catalysts in multiphase selective hydrogenation of cinnamaldehyde using toluene and pressurized carbon dioxide

The recyclability of water-soluble ruthenium–phosphine complex catalysts was investigated in water–toluene and in water–pressurized carbon dioxide systems for selective hydrogenation of trans-cinnamaldehyde (CAL). For the first hydrogenation run, the selectivity for cinnamyl alcohol (COL) is high for both toluene and dense CO 2, because of interfacial catalysis in which the reaction mainly occurs at the interface between the aqueous phase and the other toluene or dense CO 2 phase. The total CAL conversion and the COL selectivity decrease on the second run, more significantly with dense CO 2 than toluene. On the subsequent runs, however, less significant changes were observed. During the first run, the active metal complexes should change to much less active ones such as Ru(H) 2L n (TPPTS) m (L = COL) by accumulation of the main product of COL. This structural change may occur more easily in multiphase hydrogenation with dense CO 2 than that with toluene, probably because the solubility in the dense CO 2 gas phase is even smaller than that in toluene. For homogeneous reaction of COL in aqueous phase, Ru(H) 2L n (TPPTS) m catalyzes the isomerization to HCAL compared with the hydrogenation to hydrocinnamyl alcohol. With those complexes, however, the selectivity for COL is still comparable to that for HCAL for multiphase hydrogenation reactions because the hydrogenation of an ampholytic substrate of CAL occurs mainly at interface between water and toluene or dense CO 2 gas phase. Interactions of CO 2 molecules with CAL would also increase the reactivity of carbonyl group of the substrate.

Theoretical Investigation of the Selective CC Hydrogenation of Unsaturated Aldehydes Catalyzed by [{RuCl2(mtppms)2}2] in Acidic Media

Density functional theory has been applied to identify possible reaction intermediates for the catalytic C=C hydrogenation of cinnamaldehyde, which occurs in acidic aqueous solutions in the presence of water-soluble ruthenium phosphine complexes. On the basis of ONIOM calculations, two different active species and, hence, two pathways were proposed. The C=C bond hydrogenation takes place through the insertion of the terminal carbon atom into the Ru-H bond and subsequent protonation of the other carbon by hydroxonium ions present in the solution. We find that water is directly involved in several steps of the reaction, either as a protonating/deprotonating agent or as a coordinating ligand. Selectivity against C=O hydrogenation is due to the much higher barrier of either C insertion or O insertion into the Ru-H bond as compared to that of the C insertion in the case of the C=C functionality.

Synthesis, characterization and structure of ruthenium(II) phosphine complexes with N-heterocyclic thiolate ligands

The [Ru(dppb)(mbt) 2], mbt = 2-mercaptobenzothiazole, complex, isolated from the reaction of the mer-[RuCl 3(dppb)(OH 2)] complex with the 2,2′-dithiobis(benzothiazole), mbts, was characterized by spectroscopic and electrochemical techniques ( E 1/2 = 0.78 V versus NHE) and its structure was determined by crystal X-ray analysis. The structural analysis suggests that the S–S bond of the mbts ligand is cleaved, thus forming two four-membered chelate rings coordinated to the ruthenium through the N,S-donor atoms of the mbt reduced ligands, with an average bite angle of 67.295(11)°. The 1H and 13C NMR signals observed for mbts ligand coordinated to the metal center, the changes in the vibrational spectra, and the appearance of a MLCT band in the electronic spectrum of the complex point for the reduced state of the ruthenium metal center, Ru II. These reducing processes are suggested to be due to the methanol interference, which is observed to be strongly affected by N-methylmorpholine. The cytochrome c electrochemistry was analyzed by using the SAMs formed by the mbts and the [Ru(dppb)(mbt) 2] complex on gold, with only the former presenting electroactivity.

Selective hydrogenation of cinnamaldehyde using ruthenium–phosphine complex catalysts with multiphase reaction systems in and under pressurized carbon dioxide: Significance of pressurization and interfaces for the control of selectivity

The selective hydrogenation of trans-cinnamaldehyde (CAL) has been investigated with several types of multiphase reaction systems using Ru–phosphine complex catalysts in the presence of high-pressure CO 2. The selective formation of an unsaturated alcohol, cinnamyl alcohol (COL), can be achieved in an organic solvent free two-phase system, which includes the liquid (CAL, Ru complex) and gas (H 2, CO 2) phases. Both total conversion and COL selectivity are enhanced with increasing CO 2 pressure. This enhancement is due to the dissolution of CO 2 molecules into the CAL phase, which promotes the dissolution of H 2 and activates the reactivity of the carbonyl group of CAL molecules, and a high concentration of CAL in the reaction medium. The high COL selectivity can also be obtained in three- and two-phase reaction systems, which include a gas (H 2, CO 2) phase, a liquid (water-dissolving Ru complex) phase, and/or another liquid phase (CAL). The COL selectivity is high irrespective of CO 2 pressure because of a water–CAL interface or a water–CO 2 interface as a main reaction locus, but the total conversion is not enhanced by pressurization with CO 2, and it decreases at elevated CO 2 pressure under the two-phase conditions because of a simple dilution effect. In contrast, the highly selective formation of COL is not possible in a homogeneous dense CO 2 gas phase or in a two-phase system that includes a gas (H 2) phase and a liquid (DMF, CAL, Ru complex) phase. Pressurization with CO 2 is not effective in improving the conversion and COL selectivity for these systems.

Evaluation of strategies for the immobilization of bidentate ruthenium–phosphine complexes used for the reductive amination of carbon dioxide

Different routes for the immobilization of highly active bidentate ruthenium–phosphine complexes (RuCl 2(dppe) 2 and RuCl 2(dppp) 2) on silica have been explored and the resulting heterogeneous catalysts were evaluated concerning activity and stability when applied to the formylation of functionalized amines, such as 3-methoxypropylamine, in supercritical carbon dioxide. Two fundamentally different immobilization strategies were applied: covalent linkage and coordinative anchoring of the active complex. The latter immobilization method resulted in strong leaching of the complex under reaction conditions. Structural and textural properties of the heterogeneous catalysts were characterized using various methods, including X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and inductively coupled plasma optical emission spectroscopy (ICP-OES). Particular attention was given to a thorough characterization of the catalysts when subjected to reuse. XAS in fluorescence and transmission mode provided deeper insight into the observed deactivation phenomena. Despite the low concentration of Ru in solution (ca. 50 ppm) the structural changes could be resolved with both detection modes.

Synthesis, characterization and reactivity of polypyridyl ruthenium(II) carbonyl complexes with phosphine derivatives: Ruthenium–carbon bond labilization based on steric and electronic effects

Ruthenium phosphine complexes with a CO ligand [Ru(tpy)(PR 3)(CO)Cl] + (tpy = 2,2′:6′,2″-terpyridine, R = Ph or p-tolyl), were prepared by introduction of CO gas to the corresponding dichloro complexes at room temperature. New carbonyl complexes were characterized by various methods including structural analyses. They were shown to release CO following the addition of several N-donors to form the corresponding substituted complexes. The kinetic data and structural results observed in this study indicated that the CO release reactions proceeded in an interchange mechanism. The molecular structures of [Ru(tpy)(PPh 3)(CO)Cl]PF 6, [Ru(tpy)(P( p-tolyl) 3)(CO)Cl]PF 6 and [Ru(tpy)(PPh 3)(CH 3CN)Cl]PF 6 were determined by X-ray crystallography.

Asymmetric hydrogenation of aromatic ketones in ionic-liquid media catalyzed by Ru-TPPTS–(1 S,2 S)-DPENDS complexes

The catalytic performance of ruthenium phosphine complexes using (1 S,2 S)-DPENDS [(1 S,2 S)-1,2-diphenyl-1,2-ethylene diamine sulfonate disodium] as a chiral modifier in the asymmetric hydrogenation of aromatic ketones was examined in a series of hydrophilic ionic liquids [RMIM] +[ p-CH 3C 6H 4SO 3] − (R = ethyl, butyl, octyl, dodecyl). The synergistic effect between (1 S,2 S)-DPENDS and KOH significantly accelerated the reaction and enhanced the enantioselectivity. An ee value of 84.8% was obtained in the asymmetric hydrogenation of acetophenone under the optimized conditions. The products were conveniently separated with cyclohexane extraction, and both the ruthenium catalyst and (1 S,2 S)-DPENDS were kept in the ionic liquid and could be reused.

2-(Aminomethyl)pyridine−Phosphine Ruthenium(II) Complexes: Novel Highly Active Transfer Hydrogenation Catalysts

The complexes trans,cis-RuCl2(PPh3)2(ampy) (1) and trans-RuCl2[Ph2P(CH2)4PPh2](ampy) (2) have been prepared in high yield by reaction of RuCl2(PPh3)3 and RuCl2(PPh3)[Ph2P(CH2)4PPh2] with 2-(aminomethyl)pyridine (ampy) at room temperature by PPh3 displacement. Heating compound 1 in refluxing toluene leads to the isomer cis,cis-RuCl2(PPh3)2(ampy) (3), which has been proven to be a good precursor for the preparation of the complexes cis-RuCl2(PP)(ampy) [PP = (S,S)-Chiraphos, 4; Ph2P(CH2)3PPh2, 5; (S,S)-Skewphos, 6; Ph2P(CH2)4PPh2, 7; (R,R)-Diop, 8] by displacement of two PPh3 with the appropriate diphosphine. The derivatives cis-RuCl2(PP)(ampy) [PP = (R,S)-Josiphos, 9; (R,S)-tBu-Josiphos, 10] have been synthesized from RuCl2(PPh3)3 and PP followed by addition of ampy. The chiral complexes 4, 6, 8, 9, and 10 are formed stereoselectively, as inferred by NMR data in solution. For the derivatives 7 and 9 the molecular structures have been determined by X-ray measurements. The monohydride complex trans,cis-RuHCl(...

Hydrogen Elimination from a Hydroxycyclopentadienyl Ruthenium(II) Hydride: Study of Hydrogen Activation in a Ligand−Metal Bifunctional Hydrogenation Catalyst

At high temperatures in toluene, [2,5-Ph(2)-3,4-Tol(2)(eta(5)-C(4)COH)]Ru(CO)(2)H (3) undergoes hydrogen elimination in the presence of PPh(3) to produce the ruthenium phosphine complex [2,5-Ph(2)-3,4-Tol(2)-(eta(4)-C(4)CO)]Ru(PPh(3))(CO)(2) (6). In the absence of alcohols, the lack of RuH/OD exchange, a rate law first order in Ru and zero order in phosphine, and kinetic deuterium isotope effects all point to a mechanism involving irreversible formation of a transient dihydrogen ruthenium complex B, loss of H(2) to give unsaturated ruthenium complex A, and trapping by PPh(3) to give 6. DFT calculations showed that a mechanism involving direct transfer of a hydrogen from the CpOH group to form B had too high a barrier to be considered. DFT calculations also indicated that an alcohol or the CpOH group of 3 could provide a low energy pathway for formation of B. PGSE NMR measurements established that 3 is a hydrogen-bonded dimer in toluene, and the first-order kinetics indicate that two molecules of 3 are also involved in the transition state for hydrogen transfer to form B, which is the rate-limiting step. In the presence of ethanol, hydrogen loss from 3 is accelerated and RuD/OH exchange occurs 250 times faster than in its absence. Calculations indicate that the transition state for dihydrogen complex formation involves an ethanol bridge between the acidic CpOH and hydridic RuH of 3; the alcohol facilitates proton transfer and accelerates the reversible formation of dihydrogen complex B. In the presence of EtOH, the rate-limiting step shifts to the loss of hydrogen from B.

Reactions of Ruthenium(0) Phosphine Complexes with Diphenylacetylene

Heating diphenylacetylene with [Ru(CO)2(PPh3)3] in toluene under reflux provides the 2-phenylindenone complex [Ru(η4-OCCPhCHC6H4)(CO)(PPh3)2], arising from C−H activation of one ortho-proton of diphenylacetylene, hydroruthenation of the triple bond, and cyclization incorporating one carbonyl ligand. Both phosphines are replaced by 1,2-bis(diphenylphosphino)ethane to provide [Ru(η4-OCCPhCHC6H4)(CO)(dppe)]. In contrast, heating diphenylacetylene with [Ru(CO)3(PPh3)2] in toluene under reflux generates the tetraphenylcyclopentadienone complex [Ru(η4-OCC4Ph4)(CO)2(PPh3)] in high yield, via [2+2+1] alkyne and CO cyclization. The crystal structures of [Ru(η4-OCCPhCHC6H4)(CO)(PPh3)2], [Ru(η4-OCCPhCHC6H4)(CO)(dppe)], [Ru(η4-OCC4Ph4)(CO)2(PPh3)], and [Ru(η-PhC⋮CPh)(CO)2(PPh3)2] solvates are reported.

Catalytic deallylation of allyl- and diallylmalonates.

Substituted allylmalonates undergo the selective C-C bond cleavage in the presence of triethylaluminum and a catalytic amount of nickel and ruthenium phosphine complexes, resulting in the loss of the allyl moiety and formation of monosubstituted malonates. Comparison of reactivity of the nickel and ruthenium complexes showed that the use of the former is general with respect to the structure of the substituted allylmalonates, and the activity of the latter depended on the substitution pattern of the double bond of the allylic moiety. The smooth deallylation may encourage the use of the allyl group as a protective group for the acidic hydrogen in malonates.

Ruthenium(II)‐Catalyzed Homo‐Diels—Alder Reactions of Disubstituted Alkynes and Norbornadiene.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Ruthenium(II)-catalyzed homo-Diels–Alder reactions of disubstituted alkynes and norbornadiene

The homo-Diels–Alder (HDA) reaction of norbornadiene (NBD) and internal functionalized alkynes leading to 8,9-disubstituted deltacyclenes using readily available electron-rich phosphine–ruthenium(II) catalysts is described.

Homogeneous hydrogenation of carbon dioxide and bicarbonate in aqueous solution catalyzed by water-soluble ruthenium(II) phosphine complexes

The water-soluble Ru(II)–phosphine complex, [{RuCl 2( mTPPMS) 2} 2] was found a suitable catalyst for the hydrogenation of NaHCO 3 to NaHCO 2 in aqueous solution under mild conditions with catalyst turnover frequencies (TOFs) in the range of 35–50 h −1 at 50 °C and 10 bar total pressure. The suggested reaction mechanism involves the formation of Ru(II)-hydrides of the general formula [RuHX( mTPPMS) 4] where X=H −, HCO 3 − or HCO 2 −. At 80 °C and 95 bar total pressure, the reduction of NaHCO 3 proceeded with high reaction rate (9600 h −1) hitherto unobserved in purely aqueous solutions. The reactions do not require the presence of organic amine additives, however, the addition of quinoline increased the rate considerably. Aqueous suspensions of calcium carbonate could also be hydrogenated with CO 2/H 2 gas mixtures.

Thermoregulated phase-separable phosphine ruthenium complex for hydrogenation catalysis

Thermoregulated phase-separable Ru3(CO)12/PETPP (P-[p-C6H4O(CH2CH2O)nH]3, n=6) complex was applied in the hydrogenation catalysis for the first time. With styrene as the model substrate, under the optimum conditions of P(H2)=2.0 MPa, T=90 °C, the conversion of styrene and yield of ethylbenzene were 100 and 99.5%, respectively. After reaction, the catalyst could be easily separated from reaction mixture and reused for ten times without loss of activity has been observed.