Evidences of release and catch mechanism in the Heck reaction catalyzed by palladium immobilized on highly cross-linked-supported imidazolium salts

https://doi.org/10.1016/j.molcata.2014.02.025Get rights and content

Highlights

  • Synthesis of alkenes is efficiently promoted by a silica-supported highly cross-linked imidazolium-based palladium catalyst.

  • Important differences between Heck and Suzuki reactions have been evidenced when the reactions were carried out in the presence of the scavenging support.

  • The imidazolium-based support is able to recapture the leached Pd species.

  • Suzuki reaction between aryl bromides and phenylboronic acid is catalyzed by leached Pd species.

  • Pd species could be recaptured giving a product with a minimal metal contamination.

Abstract

Palladium (10 wt%) on a highly cross-linked imidazolium-based material was used as catalyst in 0.1 mol% in the Heck reaction between several alkenes and aryl iodides. Products were obtained from good to high yields. Deeper investigations showed a release of Pd species in solution and their capture by the imidazolium-based support. When a sixfold amount of support was employed the re-captured Pd species (0.5–0.6 wt%) were not anymore catalytically active. This result represents a new interesting aspect of this work since the highly cross-linked imidazolium-based material can act also as Pd scavenger avoiding the release of the metal in solution. Important differences between Heck and Suzuki reactions have been evidenced when the reactions were carried out in the presence of the scavenging support.

Introduction

Heck coupling reaction has become a mainstay of modern synthetic organic chemistry for the formation of the carbon–carbon bonds [1], [2], [3], [4], [5]. The importance of coupling products from Suzuki, Heck and other Csingle bondC coupling reactions as components of many kinds of compounds, mainly pharmaceuticals and natural products [6], [7], as well as in the field of engineering materials, such as conducting polymers [8], [9], [10] has attracted enormous interest from the chemistry community. A plethora of palladium-based catalytic systems have been developed with the aim of obtaining new catalysts displaying increased activity and selectivity [11], [12], [13], [14], [15], [16].

The Heck reaction has been one of the Pd-catalyzed processes extensively investigated in ionic liquids (ILs). As reaction media have been used onium salts, pyridinium and imidazolium salts [17], [18], [19], [20], [21] and more recently supported ILs and the so-called task-specific ionic liquids, TSILs [22], [23], [24], [25]. However, the reactions which involve ionic liquids as solvents suffer from severe problems related with high cost as well as high viscosity of ionic liquids. To overcome these drawbacks, adsorbed ionic liquids or covalently linked ionic liquids to several supports have been developed. These materials have found interesting applications for both metal catalyzed and organocatalyzed reactions [26]. Imidazolium-based networks serve as the reaction phase in which the homogeneous catalyst is dissolved. This class of advanced materials shares the properties of true ionic liquids, behaving as bulk ionic liquids and the advantages of a solid support. In several cases the Heck reaction, takes place through the formation of soluble complexes/Pd clusters formed from supported PdNPs containing ILs moieties either deposited on a solid support as a thin film [27] or covalently attached to the solid (organic and inorganic) [28], [29]. In most instances, the release of soluble species has been observed [30]. The most important question is if such soluble species are recaptured at the end of the reaction [31], [32], [33]. Although the recapture of Pd-based catalytic species has already been described it is important to get further evidences of such “release and catch” mechanism [34] in order to fully understand the general applicability of this phenomenon.

Recently, we have prepared several supported imidazolium salts on silica gel by using a new approach, i.e. the thiol-ene reaction between a mercaptopropyl-modified silica gel and bis-vinylimidazolium salts. These materials have been employed for the non-covalent immobilization of organic molecules, such as a ionic liquid-tagged proline [35] or TEMPO catalysts [36]. On the other hand, the same supports have been successfully employed for palladium nanoparticles immobilization. The latter materials have been used in the Suzuki–Miyaura reaction between arylboronic acids and arylhalides to give biaryls in high yields both under batch [37], [38] and continuous-flow conditions [39]. The interesting aspect of these materials is the high imidazolium salt content which allows a high Pd content (10 wt%). Since these catalysts were used in only 0.1 mol%, only 1 mg of catalytic material was needed per mol of substrate. Moreover, the Suzuki–Miyaura reaction under flow conditions was carried out by placing catalyst and solid base (K2CO3) in two separate columns. Here we report preliminary observation about the use of our catalytic materials toward the Heck reaction under batch conditions as a first step for a study under flow conditions, exploring scope and limitations and trying to get evidences of a “release and catch” mechanism [34]. Moreover, the ability of highly cross-linked imidazolium-based material to act as Pd scavenger from its solutions or from Suzuki reactions [39], [40] could be extended to Heck reactions allowing the obtainment of products with a minimal metal contamination.

Section snippets

General

The NMR spectra were recorded on a Bruker 300 MHz spectrometer. Mass spectra were recorded on a Shimadzu GCMS-QP2010. Carbon and nitrogen contents were determined by combustion analysis in a Fisons EA 1108 elemental analyzer. EDX values are an average of several measures, at least 10 per sample. XPS values are the average of three different points.

General procedure for the Heck reaction

To a round-bottom flask catalyst 1a (0.1 mol%, 1 mg), alkene (1.5 mmol), aryliodide (1 mmol), triethylamine (2 mmol) and DMF/H2O (4 mL + 1 mL) were added. The

Results and discussion

As catalyst we have employed material 1a (Fig. 1) which has been prepared as previously reported [37]. As a first approach, we have investigated the reaction between styrene and iodobenzene (Table 1). Two different bases, namely triethylamine and potassium carbonate, and several solvents were preliminarily screened. The best reaction condition was found when a 4:1 DMF/water solvent mixture in the presence of triethylamine as base was employed. The presence of water increased the yield (Table 1,

Conclusions

We have demonstrated that palladium (10 wt%) on a highly cross-linked imidazolium-based material is an efficient catalyst when used in 0.1 mol%, for the Heck reaction between aryl iodides and alkenes (styrene derivatives, methyl vinylketone and methyl acrylate) in DMF/H2O in the presence of TEA at 90 °C. Under these conditions such catalyst released Pd species in solution and the leached Pd species catalyzed the reaction, but in the presence of a sixfold amount of the imidazolium-based support

Acknowledgements

We gratefully acknowledge the Università degli Studi di Palermo, the Università degli Studi di Perugia, the University of Namur for financial support and the “Centro Grandi Apparecchiature – UniNetLab – Università di Palermo funded by P.O.R. Sicilia 2000–2006, Misura 3.15 Quota Regionale”.

References (56)

  • N.J. Whitcombe et al.

    Tetrahedron

    (2001)
  • W.A. Herrmann et al.

    J. Organomet. Chem.

    (1999)
  • R.B. Bedford et al.

    Coord. Chem. Rev.

    (2004)
  • V. Sans et al.

    Catal. Today

    (2012)
  • M.I. Burguete et al.

    J. Catal.

    (2010)
  • J.M. Richardson et al.

    J. Catal.

    (2007)
  • F. Zhao et al.

    J. Mol. Catal. A: Chem.

    (2002)
  • I.P. Beletskaya et al.

    Chem. Rev.

    (2000)
  • L. Yin et al.

    Chem. Rev.

    (2006)
  • L. Yin et al.

    Chem. Rev.

    (2007)
  • D. Astruc

    Inorg. Chem.

    (2007)
  • J.G. De Vries

    Can. J. Chem.

    (2001)
  • C. Torborg et al.

    Adv. Synth. Catal.

    (2009)
  • Z. Peng et al.

    J. Am. Chem. Soc.

    (1997)
  • F. Babudri et al.

    J. Mater. Chem.

    (2004)
  • Y. Lim et al.

    J. Am. Chem. Soc.

    (2011)
  • V. Farina

    Adv. Synth. Catal.

    (2004)
  • N. Marion et al.

    Acc. Chem. Res.

    (2008)
  • Á. Molnár

    Chem. Rev.

    (2011)
  • Palladium-Catalyzed Coupling Reactions: Practical Aspects and Future Developments

    (2013)
  • A.J. Carmichael et al.

    Org. Lett.

    (1999)
  • H. Zhao et al.

    Aldrichim. Acta

    (2002)
  • C.C. Cassol et al.

    J. Am. Chem. Soc.

    (2005)
  • V.I. Pârvulescu et al.

    Chem. Rev.

    (2007)
  • F. Bellina et al.

    Molecules

    (2010)
  • J.C. Xiao et al.

    Org. Lett.

    (2004)
  • L. Zhou et al.

    Synthesis

    (2006)
  • Y. Liu et al.

    Curr. Org. Chem.

    (2009)
  • Cited by (39)

    • Generation of I-, ArS- and ArSe- substituted pyrrolo[3,4–c]pyridine derivatives using copper iodide as an iodinating agent

      2021, Tetrahedron Letters
      Citation Excerpt :

      They are immensely important intermediates in synthetic organic chemistry [1]. Aryl halides are extensively used in cross-coupling reactions such as the Sonogashira coupling [2], Mizoroki−Heck reaction [3], Ullmann condensation [4] and Suzuki−Miyaura cross-coupling [5]. Besides this they are also used for the generation of organometallic reagents, for free-radical intermediates and for nucleophilic substitution reactions [6].

    • Formation and stabilization of nanosized Pd particles in catalytic systems: Ionic nitrogen compounds as catalytic promoters and stabilizers of nanoparticles

      2021, Coordination Chemistry Reviews
      Citation Excerpt :

      However, very low (less than 0.1%) or even undetectable Pd losses were observed after catalytic runs in some works [415,418,421,428,432,436,445,448,449]. The later results may be explained by a release and catch mechanism according to which leached Pd species can be captured back by the catalyst support after the catalytic reaction approaches completion [420]. Total Pd losses can depend significantly not only on the method used for immobilization but also on the conditions of a catalytic reaction [421,422,443].

    • Synthesis and characterization of a new zwitterionic palladium complex as an environmentally friendly catalyst for the Heck-Mizoroki coupling reaction in GVL

      2019, Molecular Catalysis
      Citation Excerpt :

      According to Fig. 3, and Table S5, for complex 1, the HOMO and LUMO orbitals are distributed over the ligand and only 3% of these two frontier molecular orbitals is located on the palladium. The large energy gap between HOMO and LUMO (3.35 eV) illustrates the low chemical activity and kinetic stability of this complex [24]. The solid-state structure of complex 1 was determined by X-ray crystallography and the ORTEP of the complex was shown with their atom-labeling scheme in Fig. 4.

    • Preparation and characterization of a new bis-layered supported ionic liquid catalyst (SILCA) with an unprecedented activity in the Heck reaction

      2019, Journal of Catalysis
      Citation Excerpt :

      Since the activity of this palladium is still extremely high, we consider that the dimerized form represent a reservoir of the active species. The release and catch mechanism for the Heck reaction was already reported [56] and it comes from the ability of the moiety to retake Pd. In our case, the nitrogen containing and mainly the TMG molecule has a function to harvest leached Pd in the form of nanoparticles.

    View all citing articles on Scopus
    View full text