Follow SiliCycle on Facebook Follow SiliCycle on Twitter Follow SiliCycle on LinkedIn Watch our videos on Youtube

entree SiliaCat

Stille Coupling Using SiliaCat Pd Catalysts

The Stille coupling is a versatile reaction for C-C bond formation. It is a coupling between a halide and an organotin compound. This reaction is widely used in synthesis, but a major drawback is the toxicity of the tin compounds involved. In Stille couplings, a Pd0 or PdII catalyst is required, and it must be compatible with a wide variety of functional groups (very few limitation on the R-group). SiliCycle has developed catalysts that are highly efficient for Stille couplings, as shown below.

Note: SiliaCat Pd0 results were not available at the time of printing.

StilleCouplingReaction1.gif

Catalyst Concentration and Solvent Effects

Increasing the amount of the catalyst, for the same solvent and at a constant substrate concentration, improves kinetics (see table below). With a mol % of 0.25, the reaction was not completed in 22 h. With a mol % of 2.0, the reaction was completed in 17 h.

As a general rule, if the solvent and the concentration of the substrate are kept constant, increasing the amount of the catalyst, thus increasing the member of the active sites, will speed up the kinetics of the reaction.

This table also shows the importance of the solvent. At low catalyst concentration, 0.25 mol % in dioxane, the reaction was not completed in 22 h. However, under the same conditions but with toluene as the solvent, the reaction was completed in 16 h. In dioxane, the same activity is observed for a concentration of 2.0 mol %. The solvent is responsible for diffusion of the substrate to the active sites, so the better the diffusion, the higher the kinetics will be.

In all experiments, determining the optimal quantity of SiliaCat in respect to the solvent should be done.

Catalyst Concentration and Solvent Effects
SiliaCat DPP-Pd
(mol %)
Solvent
(M)
Time
(h)
Conversion
(%)
2.0
Dioxane (0.1 M)
17
99
0.5
Dioxane (0.1 M)
20
100
0.25
Dioxane (0.1 M)
22
74
0.25
Toluene (0.1 M)
16
99

 

SiliaCat DPP-Pd Reusability and Leaching

The minimal leaching and the robustness of the organoceramic matrix are important factors that allow SiliaCat DPP-Pd to be reused several times.

CatalystReusabilityLeaching

 

SiliaCat DPP-Pd Reusability and Leaching
Reusability
Conversion
(%)
Pd Leaching
(ppm)
1st
100
3.0
2nd
100
1.7
3rd
100
2.3
4th
100
2.3

 

Catalytic Activity and Additive CsF Influence

Reactions were performed at reflux until the GC/MS analysis showed maximum conversion. Anhydrous conditions are not required.

Catalytic Activity and Additive CsF Influence
Substrate (R)
Halide (X)
SiliaCat DPP-Pd
(mol %)
Additive
(eq.)
Solvent
(M)
Time
(h)
Conversion
(%)
4-CN
Br
2
-
Dioxane (0.1 M)
18
87
4-F
Br
10
-
Dioxane (0.1 M)
24
99
4-F
Br
10
CsF (2)
Toluene (0.1 M)
24
100
H
Br
10
-
Toluene (0.1 M)
24
100
4-CH3
Br
10
CsF (2)
Dioxane (0.1 M)
24
100
4-OCH3
Br
10
CsF (2)
Dioxane (0.1 M)
24
100
H
I
10
CsF (2)
Toluene (0.1 M)
24
100
4-NO2
I
2
-
Dioxane (0.1 M)
18
88
Note: R'SnBu3 was vinyl (1.1 eq.)

 

SiliaCat DPP-Pd vs Competitive Catalysts

Comparative analysis with other Pd catalysts available on the market demonstrates the SiliaCat DPP-Pd to be comparable or better in standard Stille conditions. Table at right shows conversion %.

SiliaCat DPP-Pd Reusability and Leaching
SiliaCat DPP-Pd
Escat 1351
Encat 30
Royer
Catalyst
Pd(PPh3)4
Pd(OAc)2
99
44
95
90
72
20

 

Stille Coupling Typical Experimental Procedure

Conventional Experimental Conditions

Reaction - All products except the catalyst are added to a round bottom flask equipped with a condenser and a magnetic stirrer. Bring mixture to reflux, and after 10 minutes (when the solution is homogeneous) add the required quantity of catalyst.

Work-up

Once the reaction is complete (determined by TLC or GC-MS), follow the same work-up procedure as for Suzuki coupling standard conditions.

Experimental Conditions - Stille Coupling
Products
Standard Conditions for 1 eq of:
Ar-Iodide & Ar-Bromide
Base [K2CO3]
1.0- 2.0 eq. (usually 1.1 eq.)
Additive (CsF)
If needed, add 2.0 eq. for higher conversion
SiliaCat Catalyst
0.25 - 10.0 mol %
(typ.: 2 mol % for -I and 2 - 10 mol % for -Br)
Best Solvents
(HPLC Grade)
Dioxane (0.1 M) or Toluene (0.1 M)
*Note: molar concentration is related to the substrate.

 

5 Item(s)

Set Descending Direction
per page

List  Grid 

  1. SiliaCat DPP-Pd heterogeneous catalyst

    SiliaCat® Heterogeneous Catalysts DPP-Pd

    The significant costs associated with precious metal catalysts and their undesired tendency to remain in organic products has generated interest for an increase in reactivity and ways to recover and reuse these metals. SiliaCat DPP-Pd is a unique diphenylphosphine palladium (II) heterogeneous catalysts made from a leach-resistant organoceramic matrix.
  2. SiliaCat® Heterogeneous Catalysts TEMPO

    SiliaCat® Heterogeneous Catalysts TEMPO

    SiliaCat® TEMPO is a heterogeneous catalyst/reagent made from a proprietary class of organosilica-entrapped radicals suitable for the selective oxidation of delicate substrates into valued carbonyl derivatives.

  3. SiliaCat® Heterogeneous Catalysts Pd0

    SiliaCat® Heterogeneous Catalysts Pd0

    SiliaCat Pd0 is a new series of patent-protected sol–gel-entrapped Pd nanocatalysts. It is made from highly dispersed Pd nanoparticles (uniformly in the range 4.0–6.0 nm) encapsulated within an organosilica matrix.
  4. SiliaCat® Heterogeneous Catalysts Pt0

    SiliaCat® Heterogeneous Catalysts Pt0

    SiliaCat Pt0 is made of organosilica physically doped with nanostructured platinum (0), and is both stable and efficient. This catalyst was successfully prepared by a novel and simple sol-gel route.
  5. SiliaCat® complete heterogeneous catalysts kit

    SiliaCat® complete heterogeneous catalysts kit

    Containing : SiliaCat DPP - Pd, Pd0, Pt0 and TEMPO

5 Item(s)

Set Descending Direction
per page

List  Grid