Monosulfonated Triphenylphosphine Research Articles

Selective reduction of alkynes to alkenes with hydrogen or formic acid catalyzed by cis,mer-[IrH2Cl(mtppms)3

In this work we have found, that the water-soluble cis,mer-[IrH2Cl(mtppms)3] (mtppms = monosulfonated triphenylphosphine Na-salt) was an excellent catalyst for reduction of terminal alkynes by hydrogen transfer from aqueous HCOOH/HCOONa mixtures. The conversions strongly depended on the pH of the reaction mixtures, and the highest rate of phenylacetylene transfer hydrogenation was observed at pH 3. The same dihydrido-Ir(III) complex actively catalyzed also the hydrogenation of terminal alkynes under mild conditions (T = 50 °C; P(H2) = 2–10 bar). Importantly, both the hydrogenation and hydrogen transfer reductions afforded exclusively the corresponding alkenes as products. Phenylacetylene and its substituted derivatives reacted smoothly, while benzylic and aliphatic alkynes were less reactive or did not react at all. It was also found, that an excess of the mtppms ligand inhibited the reaction. This was rationalized by formation of cisz-[IrH2(mtppms)4]+ which was also confirmed with multinuclear NMR spectroscopy. On the basis of the experimental results, a joint mechanism was suggested for both the hydrogenation and transfer hydrogenation pathways. The mechanism of hydrogenation and transfer hydrogenation of phenylacetylene was also studied by DFT calculations, which revealed several possibilities for protonation of a vinyl intermediate as the crucial step in formation of the styrene product.

Promoter effect of bicarbonate in hydrogenation of cinnamaldehyde catalyzed by a water-soluble Ru(II)-phosphine complex

Abstract The highly selective formation of cinnamalcohol in hydrogenation of trans-cinnamaldehyde with [{RuCl2(mtppms)2}2] + mtppms as catalyst (mtppms = monosulfonated triphenylphosphine) in aqueous solution was substantially accelerated by NaHCO3 (in 20–50 mol% quantities relative to cinnamaldehyde). More than double conversion compared to bicarbonate-free systems was observed at n(NaHCO3)/n(Ru) = 20. Prehydrogenation of the reaction mixture before the addition of cinnamaldehyde resulted in further rate increase (45.3% conversion vs. 13.1% in water). 1H , 13C and 31P NMR studies revealed that formate produced in hydrogenation of bicarbonate facilitated formation of trans-[Ru(H)2(H2O)(mtppms)3], a better catalyst than cis-fac-[Ru(H)2(H2O)(mtppms)3] which is the product of the reaction of [{RuCl2(mtppms)2}2] + mtppms with H2 in the absence of formate (or bicarbonate). Accordingly, NaHCO2 produced even higher rate increase than the same amount of NaHCO3.

Effect of 2-Propanol on the Transfer Hydrogenation of Aldehydes by Aqueous Sodium Formate using a Rhodium(I)-sulfonated Triphenylphosphine Catalyst

In water/2-propanol mixtures [RhCl(mtppms)(3)] (mtppms = monosulfonated triphenylphosphine) was an efficient catalyst for the selective C=C reduction of trans-3-phenyl-2-propenal (trans-cinnamaldehyde) by hydrogen transfer from formate at temperatures as low as 30 °C. An outstandingly high catalyst turnover frequency of 1214 h(-1) was determined at 70 °C. A possible mechanism of the reaction is suggested on the basis of kinetic studies and (1)H- and (31)P-NMR spectroscopic identification of the major Rh(I) species in the reaction mixtures as cis-mer-[H(2)RhX(mtppms)(3)] (X = HCOO(-) or H(2)O). It was established that a large part but not all of the rate increase observed in water/2-propanol mixtures in comparison with systems with neat water as solvent was the consequence of complete dissolution of trans-cinnamaldehyde on the effect of the co-solvent. Nevertheless, the rate showed a significant further increase with increasing 2-propanol concentration even in homogeneous solution and this was ascribed to changes in the solvent structure. The high catalyst activity in this solvent mixture allowed the transfer hydrogenation of citral. Although good to excellent conversions were observed at 30-70 °C, a useful degree of selectivity in hydrogenation of C=C vs. C=O bonds could not be achieved.

Selective hydrogenation of cinnamaldehyde and phospholipids in aqueous-organic biphasic systems with ruthenium(II) complex catalysts

Abstract The new water-soluble complex [RuH(OOc)(mtppms)3] (OOc=octanoate, mtppms=monosulfonated triphenylphosphine) was synthesized and – together with the known [RuH(OAc)(mtppms)3] (OAc=acetate) – applied for aqueous-organic biphasic hydrogenation of cinnamaldehyde as well as for hydrogenation of soybean liposomes under mild conditions. The complexes showed pronounced selectivity (up to 75%) towards the hydrogenation of the C=O function in the α,β-unsaturated aldehyde; the selectivity was influenced by the pH of the aqueous phase and the hydrogen pressure. The C=C double bonds in soybean lecithin were only slowly reduced, however, at 5 bar H2 pressure the reaction rate was sufficient to achieve substantial conversion (approximately 20% of all double bonds) in the unsaturated fatty acids.

Classical and non-classical phosphine-Ru(ii)-hydrides in aqueous solutions: many, various, and useful

Hydrogenation of the water-soluble [{RuCl(2)(mtppms)(2)}(2)] (mtppms = monosulfonated triphenylphosphine) was studied in aqueous solutions in the presence of excess mtppms both with H(2) and with aqueous HCOONa. Depending on the reductant, the pH and H(2) pressure altogether nine hydride species were identified. In acidic solutions at 1 bar H(2) pressure the known [RuHCl(mtppms)(3)] (1) and [{RuHCl(mtppms)(2)}(2)] (3) were formed, however, elevated pressure led to the formation of trans-[RuH(2)(mtppms)(4)] (11). In basic solutions at atmospheric pressure cis-fac-[RuH(2)(H(2)O)(mtppms)(3)] (12) was observed which was readily replaced by [RuH(2)(η(2)-H(2))(mtppms)(3)] (13) at higher H(2) pressures. 13 is the first water-soluble and stable η(2)-H(2) Ru(II)-complex stabilized only by monodentate phosphine ligands. [RuHBr(mtppms)(3)] (9) and [RuHI(mtppms)(3)] (10) were obtained analogously to 1. In concentrated aqueous HCOONa solutions (often used in H-transfer hydrogenations) the major species was trans-[RuH(2)(HCOO)(mtppms)](-) (14) while in dilute solutions trans-[RuH(2)(H(2)O)(mtppms)(3)] (15) could be observed. Formation of these various hydride species offers an explanation for the earlier observed pH and pressure dependence of the rates and selectivities in hydrogenation of unsaturated aldehydes catalyzed by [{RuCl(2)(mtppms)(2)}(2)] + mtppms.

Free formic acid by hydrogenation of carbon dioxide in sodium formate solutions

Free formic acid was produced in hydrogenation of carbon dioxide dissolved in aqueous sodium formate solutions under H2 and CO2 pressure with the water-soluble rhodium–phosphine complex, [RhCl(mtppms)3] (mtppms = monosulfonated triphenylphosphine) as catalyst. Concentration of sodium formate, total gas pressure and the pressure ratio of H2 to CO2 were the most important factors for production of HCOOH. Up to 0.13 M concentration of HCOOH was achieved, while there was negligible formic acid production in the absence of sodium formate.

Oxidation of a Water-Soluble Phosphine and Some Spectroscopic Probes with Nitric Oxide and Nitrous Acid in Aqueous Solutions

In acidic aqueous solutions, nitrogen monoxide oxidizes monosulfonated triphenylphosphine, TPPMS(-), to the corresponding phosphine oxide. The NO-derived product is N(2)O. This chemistry parallels that reported for the reaction of NO with the unsubstituted triphenylphosphine in nonpolar organic solvents, but the rate constant measured in this work, 5.14 x 10(6) M(-2) s(-1), is greater by several orders of magnitude. This makes TPPMS(-) a useful analytical reagent for NO in aqueous solution. The increased rate constant in the present work appears to be a medium effect, and unrelated to the introduction of a single sulfonate group in the phosphine. The reaction between nitrous acid and TPPMS(-) has a 2:1 [TPPMS(-)]/[HNO(2)] stoichiometry and generates NH(2)OH quantitatively. The rate law, rate = 4k(d)[HNO(2)](2)[TPPMS(-)], identifies the second-order self-reaction of HNO(2) as the rate-limiting step that generates the active oxidant(s) for the fast subsequent reaction with TPPMS(-). It appears that the active oxidant is N(2)O(3), although the oxides NO and NO(2) derived from it may be also involved. Bimolecular self-reaction of HNO(2) also precedes the oxidations of ABTS(2-) and TMPD. Competing with this path are the acid-catalyzed oxidations of both reagents via NO(+).

Recyclable immobilized rhodium catalysts in the diastereoselective hydrogenation of unsaturated steroids

Macroreticular anion exchange resins, Amberlite IRA-900 and Amberlite IRA-96, were used to bind monosulfonated triphenylphosphine ligand via noncovalent electrostatic interactions. The resin-phosphine system was found to be very efficient at promoting the immobilization of [Rh 2(μ-OMe) 2(cod) 2]. The resulting stable Rh/TPPMS immobilized catalyst was tested in the hydrogenation of unsaturated oxosteroids (4-androstene-3,17-dione and 3β-acetoxypregna-5,16-dien-20-one). These immobilized catalysts could selectively reduce C C bonds leading to the preferential formation of the α-diastereoisomer, as in the homogeneous systems. Furthermore, these new immobilized rhodium catalysts showed good performance, easy separation and recycling without loss of activity after at least three cycles. When the immobilization of [Rh 2(μ-OMe) 2(cod) 2] was carried out in situ using either Amberlyst A27/TPPMS or the polystyrene-block-poly( m-vinyltriphenylphosphine) (PS-b-PPh 3), the catalytic activity was lower and a significant decrease was observed on recycling.

Complexation of Monosulfonated Triphenylphosphine with Chemically Modified β-Cyclodextrins: Effect of Substituents on the Stability of Inclusion Complexes

Interactions between the meta-substituted monosulfonated triphenylphosphine and chemically modified β-cyclodextrins were investigated in aqueous solution by NMR and UV–vis spectroscopy. Titration and continuous variation plots obtained from 31P NMR data indicate that the monosulfonated triphenylphosphine forms 1:1 inclusion complexes with the 2-hydroxypropylated β-cyclodextrin, the methylated β-cyclodextrin and the (2-hydroxy-3-trimethylammoniopropyl)-β-cyclodextrin chloride. These inclusion complexes are more stable that those formed with native β-cyclodextrin, confirming that poisoning of the chemically modified β-cyclodextrins by the hydrosoluble phosphine occurs when modified cyclodextrins are used as mass transfer promoters in aqueous-phase organometallic catalysis.

Hydrogenation of aqueous mixtures of calcium carbonate and carbon dioxide using a water-soluble rhodium(I)–tertiary phosphine complex catalyst

Aqueous suspensions of calcium carbonate were hydrogenated to yield calcium formate under a gas phase containing both H 2 and CO 2 . A rhodium(I)-complex of monosulfonated triphenylphosphine (mtppms), [RhCl(mtppms) 3 ] was used as catalyst. Reaction temperatures were in the range of 20–70 °C, total pressure 10–100 bar with an optimum p (CO 2 ): p (H 2 ) ratio of 1:4. Due to the mobile bicarbonate-formate equilibrium, the highest available formate concentration is decreased with increasing temperature but increased with increasing pressure. Interestingly, at 50 °C and 100 bar total pressure the yield of formate was 143% (based on CaCO 3 ) which implies the formation of free formic acid in the reaction of CO 2 from the gas phase. The dependence of the hydrogenation rate on the catalyst and ligand concentrations, as well as that of the decomposition of formate as a function of temperature were also studied. A mild method has been developed for the hydrogenation of calcium carbonate to calcium formate in aqueous suspensions under CO 2 + H 2 pressure catalyzed by [RhCl(mtppms) 3 ] (mtppms = monosulfonated triphenylphosphine) at 20–70 °C and 10–100 bar total pressure. In certain cases the yield of formate exceeded 100% (based on CaCO 3 ) which implies the concomitant hydrogenation of carbon dioxide, too.

Thermodynamic insight into the origin of the inclusion of monosulfonated isomers of triphenylphosphine into the β-cyclodextrin cavity

Formation of inclusion complexes between the β-cyclodextrin and the potassium salt of o-, m-, and p-substituted monosulfonated triphenylphosphine derivatives was investigated in aqueous solution by NMR spectroscopy. Titration and continuous variation plots obtained from 31P and 1H NMR data indicate the formation of a 1:1 inclusion complex for the three phosphine isomers. T-ROESY NMR experiments show that in all cases a non-sulfonated aromatic ring was included into the hydrophobic cavity of β-cyclodextrin from the secondary hydroxyl groups side. The standard enthalpy and entropy of the inclusion process were estimated from the temperature dependence of the association constant. All inclusion complexes were enthalpy stabilized, but highly entropy destabilized.

The Effect of pH on the Reactions of Catalytically Important RhI Complexes in Aqueous Solution: Reaction of [RhCl(tppms)3] and trans-[RhCl(CO)(tppms)2] with Hydrogen (TPPMS=mono-sulfonated triphenylphosphine)

The Effect of pH on the Reactions of Catalytically Important RhI Complexes in Aqueous Solution: Reaction of [RhCl(tppms)3] and trans-[RhCl(CO)(tppms)2] with Hydrogen (TPPMS=mono-sulfonated triphenylphosphine)

The effect of pH on the reactions of catalytically important RhI complexes in aqueous solution: reaction of [RhCl(tppms)3] and trans-[RhCl(CO)(tppms)2] with hydrogen (TPPMS = mono-sulfonated triphenylphosphine). .

Hydrolysis and hydrogenation of [RhCl(tppms)3] (1) and trans-[RhCl(CO)(tppms)2] (2) was studied in aqueous solutions in a wide pH range (2 < pH < 11) in the presence of excess TPPMS (3-diphenylphosphinyl-benzenesulfonic acid sodium salt). In acidic solutions hydrogenation of 1 yields a mixture of cis-mer- and cis-fac-[RhClH2(tppms)3] (3a,b) while in strongly basic solutions [RhH(H2O)(tppms)3] (4) is obtained, the midpoint of the equilibrium between these hydride species being at pH 8.2. The paper gives the first successful 1H and 31P NMR spectroscopic characterization of a water soluble rhodium(I)-monohydride (4) bearing only monodentate phosphine ligands. Hydrolysis of 2 is negligible below pH 9 and its hydrogenation results in formation of [Rh(CO)H(tppms)3] (5), which is an analogue to the well known and industrially used hydroformylation catalyst [Rh(CO)H(tppts)3] (6) (TPPTS = 3,3',3''-phosphinetriyltris(benzenesulfonic acid) trisodium salt). It was shown by pH-potentiometric measurements that formation of 5 is strongly pH dependent in the pH 5-9 range, this gives an explanation for the observed but previously unexplained pH dependence of several hydroformylation reactions. Conversely, the effect of pH on the rate of hydrogenation of maleic and fumaric acid catalyzed by 1 in the 2 < pH < 7 range can be adequately described by considering solely the changes in the ionization state of these substrates. All these results warrant the use of buffered (pH-controlled) solutions for aqueous organometallic catalysis.

The effect of phosphonium salt formation on the kinetics of homogeneous hydrogenations in water utilizing a rhodium meta-sulfonatophenyl-diphenylphosphine complex

Reaction of mono-sulfonated triphenylphosphine in water with certain activated olefins (for example maleic acid or fumaric acid) yields the corresponding phosphonium salt under very mild conditions. This interaction promotes the formation of the catalytically active species in the hydrogenation of the olefin catalyzed by the rhodium complex of the phosphine.