Ágnes Kathó

Recent developments in aqueous organometallic chemistry and catalysis

A survey of the literature published in 1995 and partly in 1994 on organometallic chemistry and catalysis shows that the field is characterized by further dynamic progress in research of industrially relevant processes, such as hydroformylation, in extension of aqueous organometallic catalysis to more and more diverse laboratory syntheses and in understanding the mechanisms of such processes.

Solution pH: A Selectivity Switch in Aqueous Organometallic Catalysis—Hydrogenation of Unsaturated Aldehydes Catalyzed by Sulfonatophenylphosphane–Ru Complexes

The equilibribrium distribution of water-soluble ruthenium hydrides [HRuCl(tppms)3 ] and [H2 Ru(tppms)4 ] (tppms = (3-sulfonatophenyl)diphenylphosphane) in the reaction with H2 is governed by the pH value. As a consequence, the selectivity in the hydrogenation of cinnamaldehyde for reaction at C=C or C=O can be completely inverted by changing the pH value (see drawing below).

Trimerisation of the Cationic Fragments [(η‐ring)M(Aa)]+ ((η‐ring) M=(η5‐C5Me5)Rh, (η5‐C5Me5)Ir, (η6‐p‐MeC6H4iPr)Ru; Aa=α‐amino acidate) with Chiral Self‐Recognition: Synthesis, Characterisation, Solution Studies and Catalytic Reactions of the Trimers [{(η‐ring)M(Aa)}3](BF4)3

The formation of [{(η-ring)M(Aa)}3](BF4)3trimers [(η-ring)M=(η5-C5Me5)Rh, (η5-C5Me5)Ir, (η6-p-MeC6H4iPr)Ru; Aa = α-amino acidate, one cation shown schematically] takes place by chiral self-recognition, the RMRMRM or SMSMSM trimers are equally configurated at the metal centres and are the only diastereomers detected. The equilibrium constant for the diastereomerisation process between both isomers depends on the solvent, amino acidate, and metal. The trimers catalyse the reduction of unsaturated aldehydes to unsaturated alcohols and the reduction of acetophenone to 2-phenylethanol with up to 75 % ee.

Enantioselective hydride transfer hydrogenation of ketones catalyzed by [(η6-p-cymene)Ru(amino acidato)Cl] and [(η6-p-cymene)Ru(amino acidato)]3(BF4)3 complexes

The new complexes (RRuSC, SRuSC)-[(η6-pCym)Ru(l-Aze)Cl] (6a, b), (RRuSC, SRuSC)-[(η6-pCym)Ru(l-Pip)Cl] (7a, b), (RRuRRuRRuSCSCSCSNSNSN, SRuSRuSRuSCSCSCSNSNSN)-[{(η6-pCym)Ru(l-Aze)}3](BF4)3 (8a, b) and (RRuRRuRRuSCSCSCSNSNSN, SRuSRuSRuSCSCSCSNSNSN)-[{(η6-pCym)Ru(l-Pip)}3](BF4)3 (9a, b) (l-Aze=l-2-azetidinecarboxylate, l-Pip=l-2-piperidinecarboxylate) were prepared, characterized and used, together with the known [{(η6-pCym)Ru(l-Pro)}3](BF4)3, 5 and [{(η6-pCym)Ru(l-Ala)}3](BF4)3, 10 (l-Pro=l-prolinate, l-Ala=l-alaninate), in hydride transfer reduction of acetophenone, a series of substituted acetophenones and several other ketones with moderate to high conversions and enantioselectivities up to 86% e.e.

The effects of pH on the molecular distribution of water soluble ruthenium(II) hydrides and its consequences on the selectivity of the catalytic hydrogenation of unsaturated aldehydes

Abstract The effect of pH on the formation and equilibrium distribution of the water soluble ruthenium hydrides [HRuCl(TPPMS) 2 ] 2 , [HRuCl(TPPMS) 3 ] and [H 2 Ru(TPPMS) 4 ] (TPPMS=(3-sulfonatophenyl)diphenylphosphine sodium salt) was studied in aqueous solution by pH-potentiometric and 1 H and 31 P NMR methods. Depending on the pH, [RuCl 2 (TPPMS) 2 ] 2 and its hydrido-derivatives hydrolyse extensively, giving rise to formation of hydroxo-ruthenium complexes. It was established that at pH≤3.3 the dominant ruthenium(II) species was [HRuCl(TPPMS) 3 ], while at pH≥7 it was [H 2 Ru(TPPMS) 4 ]. While [HRuCl(TPPMS) 3 ] catalyzed the slow, selective hydrogenation of the CC bond in trans -cinnamaldehyde, [H 2 Ru(TPPMS) 4 ] was found an active and selective catalyst for CO reduction. Consequently, the selectivity of the hydrogenation of trans -cinnamaldehyde could be completely inverted by minor changes in the solution pH, shifting the equilibrium between [HRuCl(TPPMS) 3 ] and [H 2 Ru(TPPMS) 4 ].

Water-soluble analogs of [RuCl3(NO)(PPh3)2] and their catalytic activity in the hydrogenation of carbon dioxide and bicarbonate in aqueous solution

The new water-soluble ruthenium-nitrosyl complexes [RuCl3(NO)(TPPMS)(2)] and [RuCl3(NO)(TPPTS)(2)] were synthetized and characterized by IR, H-1 and P-31 NMR spectroscopies. The NO stretching frequencies, nu(NO) = 1870 cm(-1) (TPPMS) and 1883 cm(-1) (TPPTS) suggest a linear Ru-N-O arrangements. Reactions with OH- yield the corresponding [RuCl3 (NO2)(P)(2)] derivatives, furthermore, [RuH(NO)(P)(3)] is formed with TPPMS or TPPTS, respectively, under 100 bar H-2 pressure. The new complexes are suitable precatalysts for the hydrogenation of carbon dioxide and/or bicarbonate in aqueous solutions up to a turnover frequency of 400 h(-1) under relatively mild conditions (30 bar H-2, 70 degreesC)

Sol-gel entrapped lipophilic and hydrophilic ruthenium-, rhodium-, and iridium-phosphine complexes as recyclable isomerization catalysts

Abstract The phosphinated complexes RuCl 2 (PPh 3 ) 3 , 1 , RhCl(PPh 3 ) 3 , 2 , IrCl(CO)(PPh 3 ) 2 , 3 , their water soluble sulfonated analogs RuCl 2 [Ph 2 P(3-C 6 H 4 SO 3 Na)] 2 · 4H 2 O, 4 , RhCl[Ph 2 P(3-C 6 H 4 SO 3 Na)] 3 · 4H 2 O, 5 , IrCl(CO)[Ph 2 P(3-C 6 H 4 SO 3 Na)] 2 , 6 , as well as the dirhodium compounds trans -[Rh(CO)(PPh 3 )(μ-pz)] 2 , 7 , and trans -[Rh(CO)(PPh 3 )(μ-Cl)] 2 , 9 were entrapped physically in SiO 2 sol-gel matrices. Replacement of the PPh 3 ligands in the two latter complexes by Ph 2 P(CH 2 ) 2 Si(OEt) 3 groups enabled to bind of the dirhodium complexes chemically to the matrix backbone via the silyloxy functions. The activity of the immobilized complexes as allylbenzene isomerization catalysts was studied and compared. Entrapped complex 4 was found to be most efficient catalyst.

Molecular catalysis in liquid multiphase systems

The possibilities of using liquid-liquid biphase or multiphase reaction systems for organometallic catalysis are discussed. An overview of important industrial two-phase processes, including – among others – the Shell α-olefin process and the Ruhrchemie/Rhône Poulenc process for propene-1 hydroformylation, is given. The special effects of the aqueous environment are discussed through the examples of the catalytic isomerization of allylbenzene and the hydrogenation of unsaturated aldehydes (pH-effects), the catalyzed deuteriation of itaconic acid from D2O as the deuterium source (micellar effects), the reduction of carbon dioxide to formic acid and the spontaneous formation of phosphonium salts (stabilizing effects of hydration and protonation).

Der pH‐Wert: ein Selektivitätsschalter für die Metallkomplex‐Katalyse in wäßrigen Lösungen – die Sulfonatophenylphosphan‐Ru‐ Komplex‐katalysierte Hydrierung ungesättigter Aldehyde

Die Gleichgewichtsverteilung der wasserloslichen Rutheniumhydride [HRuCl(tppms)3] und [H2Ru(tppms)4] (tppms = (3-Sulfonatophenyl)diphenylphosphan) bei der Umsetzung mit H2 hangt vom pH-Wert ab. Damit kann die Selektivitat der Hydrierung von Zimtaldehyd durch Verandern des pH-Wertes zugunsten der Reduktion an der C = O- oder an der C = C-Gruppe eingestellt werden (siehe unten).

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

Abstract 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.