Attention:

Certain features of Sigma-Aldrich.com will be down for maintenance the evening of Friday August 18th starting at 8:00 pm CDT until Saturday August 19th at 12:01 pm CDT.   Please note that you still have telephone and email access to our local offices. We apologize for any inconvenience.

Pd EnCat™ Encapsulated Palladium Catalysts

Chemfiles Volume 4 Article 7

Sigma-Aldrich is pleased to announce an agreement with Avecia to distribute Pd EnCat™ encapsulated palladium catalysts worldwide.

Homogeneous palladium catalysts are widely utilized due to their versatility, reactivity and functional group tolerance. However, using homogeneous catalysts presents some problems including:

  • Probable palladium contamination of product necessitating additional clean up
  • Palladium contamination of process equipment with associated decontamination costs
  • Heavy metal contamination of waste streams from extraction and washing solvents
  • Cost of catalyst lost during reaction and reaction work-up

Pd EnCat addresses these issues by using microencapsulation technology to immobilize the palladium, optionally with activating ligands, within a highly crosslinked polyurea matrix.

back to top 

How it’s Made



Microencapsulation of Palladium (II) Salts by in situ Interfacial Polymerization

back to top 

How it works



Substrates access the catalytic palladium sites by diffusion through the porous polyurea matrix; the metal remaining captured within.


back to top 

Advantages Of Pd EnCat™ Catalysts



  • Low residual metal levels in final crude product (typically <10ppm before purification)
  • Easy recovery of catalyst by filtration
  • Safer and easier to handle than palladium on carbon
  • Compatibility with a wide range of process technology options e.g. fixed bed, fluidized bed, trickle bed and microwave reactors
  • Efficiency and economy gains through recovery and recycling
  • No plating out of palladium on vessel walls

back to top 

Pd EnCat™ Applications

The performance of Pd EnCat is well-documented in an array of widely used transformations. The applications range from C-C bond forming processes, including Suzuki, Heck, Carbonylation, Sonogashira, and Stille coupling, to reductions of carbonyls, alkenes, nitro groups, and epoxides1-9. Selected examples are shown in Tables 1-7. Pd EnCat™ are available optionally with co-encapsulated ligands (Table 2) which simplifies removal of not only Pd but also ligand. Remarkably, these immobilized catalysts mediate high yield transformations often without significant increase in reaction times.


Pd EncatTM40 Catalyzed Suzuki Couplings

Table 1 Suzuki Coupling


Table 2 Suzuki Coupling with Co-encapsulated Phosphines


Table 3 Heck Reaction


Table 4 Carbonylation


Transfer hydrogenations eliminate the need for an external source of hydrogen gas and are readily carried out using nanoparticulate encapsulated Pd(0), Pd(0) EnCatTM 30NP1,6. This unique catalyst is significantly easier to use and safer to handle than activated palladium on carbon. Table 5 illustrates the mild conditions, high yields, and chemoselectivities achieved in the reduction of p-nitroacetophenone and benzylic epoxides. As with other Pd EnCatTM, Pd(0) EnCatTM 30NP is highly recyclable without significant loss of activity as shown (Table 6). Alternatively, chemoselective hydrogenations may be carried out by pre-activation of Pd EnCatTM to give Pd(0) EnCatTM, yielding an immobilized palladium zero catalyst which facilitates high yields and excellent chemoselectivities in a variety of reductions (Table 7)2.


Table 5 Transfer Hydrogenation with Pd(0) EnCat30 NP


Table 6 Recyclability


Hydrogenations with Pd(0) EnCatTM40

Table 7 Hydrogenation


Resistance to leaching Pd is a key advantage of the Pd EnCat™ products. Levels of Pd found in crude product are dependent on solvent (Table 8), substrate, and reaction conditions. Typically the Pd level in crude product is 10-20ppm prior to any purification. However, levels can be higher or lower and solvent selection is key to achieve minimum leaching; avoiding DMF and DMA where possible. Pd EnCat™ strongly resist swelling in the majority of solvents (Table 9) which is particularly important for scale up applications.


Table 8 Resistance to Leaching


Table 9 Resistance to Swelling


Pd EnCat™ (0.3g, 0.4 mmol/g) was weighed in to a 25ml carousel reaction tube and the solvent (20ml) added. The mixture was then heated to 800C whilst stirring via magnetic stirrer for 2 days. The mixture was allowed to cool to room temperature and filtered through a sintered funnel. The filtrate was collected and analysed for Pd content.

Solvent swell determined by measuring gain in volume of 1g sample of beads in solvent at room temperature over 2h, expressed as %.

back to top 

Frequently Asked Questions



Are there significant differences between Pd EnCat™ 30 and Pd EnCat™ 40?

While Pd EnCat™ 40 shows excellent performance in a variety of transformations, Pd EnCat™ 30, with lower matrix content, shows similar performance but with improved kinetics while maintaining the mechanically robust nature of Pd EnCat™ 40 under similar conditions. End users are encouraged to screen the sample sets for best fit to application.

What if I would like a different matrix porosity, a different ligand, or a different metal?

Avecia and Sigma-Aldrich intend to collaborate on extensions to the product line. Requests for custom EnCat™ should be directed to Avecia at encat@avecia.com.

Can you provide additional information on using Pd EnCat™?

As a supplement to the referenced literature below, request a free copy of the EnCat™ Users Guide on CD via e-mail at cdavis1@sial.com.

back to top 

Available Pd Encat™ Products



Name Matrix Content(%) % Pd (mmol/g) P (mmol/g) Ligand Units
644722
Pd EnCat™ 40
40 3.9–4.6(0.4) N/A N/A 1g
644714
Pd EnCat™ 30
30 3.9–4.6(0.4) N/A N/A 1g
644706
Pd EnCat™ TPP30
30 3.9–4.6(0.4) 0.26–0.35 Ph3P 1g
644692
Pd EnCat™ TOTP30
30 3.9–4.6(0.4) 0.15–0.20 (o-tolyl)3P 1g
653667
Pd(0) EnCat™ 30NP, Wet
30 3.7–4.6(0.4) N/A N/A 1g

(45% water, unit weight excludes water)


back to top 

Materials

     

References

  1. Transfer hydrogenation using recyclable polyureaencapsulated palladium: efficient and chemoselective reduction of aryl ketones, Jin-Quan Yu, Hai-Chen Wu, Chandrashekar Ramarao, Jonathan B. Spencer, Steven V. Ley, Chem. Comm. 2003, 678-697.
  2. Palladium Acetate in Polyurea Microcapsules: A Recoverable and Reusable Catalyst for Hydrogenations: Bremeyer, N.; Ley, S. V.; Ramarao, C.; Shirley, I. M.; Smith, S. C. Synlett. 2002, 11, 1843-1844.
  3. Polyurea-encapsulated palladium(II) acetate: a robust and recyclable catalyst for use in conventional and supercritical media, Steven V. Ley, Chandrashekar Ramarao, Richard S. Gordon, Andrew B. Holmes, Angus J. Morrison, Ian. F. McConvey, Ian M. Shirley, Stephen C. Smith, Martin D. Smith, Chem. Comm. 2002, 10, 1134-1135.
  4. Encapsulation of palladium in polyurea microcapsules, Chandrashekar Ramarao, Steven V. Ley, Stephen C. Smith, Ian M. Shirley, Nathalie DeAlmeida, Chem. Comm. 2002, 10, 1132-1133.
  5. Fully automated multi-step solution phase synthesis using polymer supported reagents: preparation of histone deacetylase inhibitors, Emma Vickerstaffe, Brian H. Warrington, Mark Ladlow, Steven V. Ley, Org. Biomol. Chem., 2003, 1, 2419-2422.
  6. Recyclable Polyurea Microencapsulated Pd(0) Nanoparticles: An Efficient Catalyst for Hydrogenolysis of Epoxides, Steven V. Ley, Claire Mitchell, David Pears, Chandrashekar Ramarao, Jin-Quan Yu, Wuzong Zhou, Organic Letters 2003, 5, No. 24, 4665-4668.
  7. Efficient batch and continuous flow Suzuki cross coupling reactions under mild conditions, catalysed by polyurea-encapsulated palladium(II) acetate and tera-nbutylammonium salts, Connie K. Y. Lee, Andrew B. Holmes, Steven B. Ley, Ian F. McConvey, Bushra Al-duri, Gary A. Leeke, Regina C. D. Santos, and Jonathan P. K. Seville, Chem. Comm. 2004, in press.
  8. Microwave assisted Leimgruber-Batcho reaction for the preparation of indoles, azaindoles and pyrroylquinolines, Jason Siu, Ian R Baxendale and Steven V. Ley, Org. Biomol. Chem., 2004, 2, 160-167.
  9. Polymer-assisted, multi-step solution phase synthesis and biological screening of histidone deacetylase inhibitors, Akanksha Bapna, Emma Vickerstaffe, Brian H. Warrington, Mark Ladlow, Tai-Ping D. Fan and Steven V. Ley, Org. Biomol. Chem., 2004, 2, 611-620.

back to top 

Related Links