Aqueous biphasic hydrogenations catalyzed by rhodium and iridium complexes modified with human serum albumin

https://doi.org/10.1016/j.apcata.2009.10.042Get rights and content

Abstract

Water soluble complexes derived from the interaction between Rh(CO)2(acac) and [Ir(COD)Cl]2, respectively, with human serum albumin (HSA), were employed in the aqueous biphasic hydrogenation of α,β-unsaturated compounds as 2-cyclohexen-1-one (I), 2-butenal (V), 3-phenyl-2-propenal (IX) and 3-aryl-2-methyl-2-propenals (XIII and XVII).

Both catalytic systems Rh/HSA and Ir/HSA showed to be very active in the hydrogenation of ketone I even at low temperature and hydrogen pressure; in particular, the rhodium based catalyst showed to be very selective affording exclusively cyclohexanone (II). The α,β-unsaturated aldehydes investigated required higher temperature (up to 60 °C) and pressure (5 MPa) to obtain good conversions. In this case Rh/HSA resulted to be more active than Ir based catalyst. In all cases both Rh/HSA and Ir/HSA were easily recycled without significant loss of activity.

Graphical abstract

The catalytic systems Rh/HSA and Ir/HSA (HSA = human serum albumin) were active in the aqueous biphasic hydrogenation of representatives α,β-unsaturated substrates. Both catalysts were easily recycled without significant loss of activity.

  1. Download : Download high-res image (80KB)
  2. Download : Download full-size image

Introduction

Homogeneous catalysis is a powerful tool in a wide range of organic syntheses. One of the major drawbacks of homogeneous catalytic processes is the difficulty to separate and reuse the catalyst. For this reason and for the consideration of the environmental aspects of chemical production, liquid–liquid two-phase systems have been developed in these last years, with the catalyst confined in one of the two phases and the product in the other phase [1]. In particular, aqueous/organic biphasic reactions are increasingly attractive using water soluble catalyst [1], [2], [3]. The most common catalysts are complexes modified with hydrophilic phosphanes, principally sulfonated phosphines as TPPTS (triphenylphosphine-3,3′,3″-trisulfonic acid trisodium salt), employed in the famous Ruhrchemie/Rhône-Poulenc biphasic process for the hydroformylation of propene [4], [5], [6], [7].

Besides hydroformylation, aqueous biphasic hydrogenation has been extensively explored; in particular, the hydrogenation of α,β-unsaturated carbonyl compounds has attracted the interest of the researchers. The selective hydrogenation of α,β-unsaturated aldehydes is a challenging problem and it strongly depends on the nature of the active metal catalyst and on the hydrogenation reaction conditions (pH, catalyst concentration, ligand amount, etc.) [8], [9], [10], [11], [12]. Generally, by analogy with Ru/PPh3 systems, the water soluble Ru/TPPTS complex selectively hydrogenates the Cdouble bondO bond; likewise, the analogous Ir/TPPTS complex is capable to reduce the carbonyl moiety, even if with a lower activity than the ruthenium derivatives. The Rh(I)/TPPTS complex hydrogenates α,β-unsaturated aldehydes into the corresponding saturated aldehydes, without decarbonylation, as in the case of 3-phenyl-2-propenal that can be selectively reduced to 3-phenylpropanal [8], [13], [14].

The research for active and selective water soluble catalysts, not containing phosphines, led to the design of new ligands and/or surfactants having different hydrophilic groups such as –COOH, NR3, –OH. [1], [2], [3]. In this context, a class of ligands, based on macromolecular substances, such as proteins, attracted the interest and a few metal complex–protein composites were patented and used by Japanese researchers for catalytic hydrogenation and oxidation reactions [15], [16]. Potential advantages of using these ligands/surfactants are either easy availability or the possibility to increase the solubility of the reagents in water so enhancing the reaction rate. Then, their peculiar complex structure could induce regio-, chemo- and enantio-selective reactions, too. Water soluble complexes derived from the interaction between Rh(CO)2(acac) and human serum albumin (HSA) were also used by us in a highly efficient and chemoselective hydroformylation reaction [17], [18], [19], [20]. On the basis of the interesting results obtained in the oxo-experiments, we decided to extend our research work to the aqueous biphasic hydrogenation of some α,β-unsaturated carbonyl compounds in the presence of Rh(CO)2(acac)/HSA (Rh/HSA) and of the complex obtained by the interaction of [Ir(COD)Cl]2 with HSA (Ir/HSA).

Section snippets

General remarks

HSA was purchased from Aldrich. Rh(CO)2(acac) and [Ir(COD)Cl]2 were obtained by Strem. 2-Cyclohexen-1-one, 2-butenal, 3-phenyl-2-propenal and 3-phenyl-2-methyl-2-propenal were Aldrich products. 3-(1,3-Benzodioxol-5-yil)-2-methyl-propenal was synthesized as described in the literature [21]. Flash chromatographies were carried out on silica gel Merck 60, 230–400 mesh. 1H NMR and 13C NMR spectra were recorded on a Bruker Avance 300, using CDCl3 or D2O as solvent. GC analyses were carried out on an

α,β-Unsaturated ketones

2-Cyclohexen-1-one (I) was chosen as model substrate to investigate the selectivity of our catalytic systems towards the hydrogenation of the carbon–carbon and carbon–oxygen double bond, respectively, in α,β-unsaturated ketones (Scheme 1).

Both the catalytic systems Rh/HSA and Ir/HSA were very active in the hydrogenation of I working at 40 °C under 5 MPa of H2, showing a quantitative conversion after 4 h. The rhodium catalyst exclusively afforded cyclohexanone (II), while the iridium catalyst gave

Conclusive remarks

The catalytic systems Rh/HSA and Ir/HSA showed to be active in the hydrogenation of representatives substrates that present in their molecules both Cdouble bondC and Cdouble bondO double bonds. In particular, the rhodium based catalyst resulted to be interesting as far as conversion and selectivity are concerned. Analogously to the above mentioned rhodium complexes modified with water soluble phosphanes [8], [9], [10], [11], [12], [13], [14], also our catalytic system Rh/HSA preferentially reduce the olefinic double

References (34)

  • B. Cornils et al.

    J. Organomet. Chem.

    (1995)
  • B. Chen et al.

    Appl. Catal. A: Gen.

    (2005)
  • H. Gulyàs et al.

    Inorg. Chim. Acta

    (2004)
  • K. Nuithitikul et al.

    Chem. Eng. Sci.

    (2004)
  • K. Nuithitikul et al.

    Catal. Today

    (2007)
  • M. Marchetti et al.

    Tetrahedron Lett.

    (2000)
  • S. Paganelli et al.

    J. Mol. Catal. A: Chem.

    (2006)
  • M. Marchetti et al.

    Chim. Ind.

    (2005)
  • J. Wilting et al.

    Biochim. Biophys. Acta

    (1979)
  • U. Krag-Hansen

    Pharmacol. Rev.

    (1981)
  • F. Joò

    Aqueous Organometallic Catalysis

    (2001)
  • E.G. Kuntz

    Chemtech

    (1987)
  • B. Cornils

    Org. Process Res. Dev.

    (1998)
  • E. Kuntz, Rhône-Poulenc Ind., Fr.Pat. 2314910, 1975; DE 2627354,...
  • J.M. Grosselin et al.

    Organometallics

    (1991)
  • Cited by (0)

    View full text