The overall goal of this procedure is to produce a 0.1 molar solution of samarium di iodide in Tetrahedran and use it in the synthesis of the Sumerian Barbier reaction with different additives. This is accomplished by first preparing samarium di iodide by simply mixing samarium metal with iodine crystals in tetrahedran under argon. The second step is to introduce the additive to the solution of samarium diod.
In this case, the effect of HMPA or nickel AK as additives in the Sumerian Barbie reaction is observed. Next, the substrates in Alco, halide and ketone are added to the reaction flask and stirred for five to 15 minutes. The final step is to quench and work up the reaction to obtain the final alcohol product.
Ultimately, using a kinetic analysis, it was determined how the mechanism of the Sumerian barbier reaction is altered with the inclusion of the different additives. This method can provide insight into some of the common issues while preparing solutions of samarium dire. Once the synthesis of samarium dire is mastered, it can be employed in wide array of other samarium mediated reductions.
Visual demonstration of this method is useful as Aserium IDE is sensitive to the oxygen, and for this reason, we commonly carry out these reactions in a glove box. However, here we'll show you that it can be carried out just as easily on the benchtop under an Argonne atmosphere Along with graduate student Kim Cho. Demonstrating the procedure will be Sada, a research scientist from my laboratory.
To begin flame dry a 50 milliliter round bottom flask and flush it with Argonne. Add a stir bar and cover the flask with a septum. Weigh out 0.2 grams of Sumerian metal and add to the flask again, flushing the flask with Argonne.
Next, add 10 milliliters of dry thoroughly Degas tetrahedran or THF, followed by 0.25. Four grams of iodine crystals add a balloon filled with Argonne through the septum. This keeps a positive pressure of Argonne atmosphere on the reaction.
Stir the solution vigorously at room temperature for over 12 hours. As Sumerian di iodide is generated, the solution passes through a variety of color changes, orange followed by yellow, which eventually turns to blue. The final Navy blue color is an indication that Samarium di iodide has formed.
In order to ensure full conversion, stir the solution for at least 12 hours before using Samarium di iodide in synthesis. Although the generation of Samarium DI is straightforward, here are some of the common issues that we would like to address. Prolonged exposure of the metal to our can lead to oxidized outer layer and some of them diad generated from this can be of inferior quality.
To overcome this grind, the metal with motor and pestle preferably under atmosphere, ensure that the THF solvent used is thoroughly DEGAS and dry. We prefer argon over nitrogen. When we make a large batch of SAM matter, we keep the summary matter steering continuously to keep it stable.
We would also like to refer to a recent work from our collaborator, professor David Proctor from the University of Manchester regarding the various aspects of generation of Samarium IDE published in the Journal of Organic Chemistry. To make the samarium di iodide HMPA complex take 10 milliliters of the freshly prepared samarium di iodide under Argonne and add 1.75 milliliters of HMPA through a syringe dropwise under Argonne, a deep purple color forms separately in a clean dry vial under Argonne. Prepare the substrate solution by adding 110 microliters of Ioane, 48 microliters of three pen and two milliliters of dried THF.
Then add the substrate solution dropwise to the Sumerian di iodide HMPA complex. Within five minutes of stirring, the purple color will start to look cloudy, indicating the end of the reaction. After the reaction is complete, expose the solution to air to quench it.
Upon stirring the color further changes to grayish white, the reaction is then worked up by adding 10 milliliters of saturated aqueous ammonium chloride. Add the solution to a separatory funnel and add five milliliters of dyl ether. After vigorous shaking, remove top organic layer and add more ethyl ether.
After extracting the aqueous layer two more times. Combine all of the organic layers. Wash the organic layer with 10 milliliters of a saturated aqueous solution of sodium thio sulfate.
Remove the bottom aqueous layer followed by a wash with water, and then finally wash with brine. Obtain the top organic layer and add magnesium sulfate to soak up any last amount of water present in solution. Pass the solution through a plug of Flo IL in order to remove excess HMPA, concentrate the solution on a rotary evaporator to obtain the barbier product.
The product can then be identified by GCMS and proton and MR.Next, we will carry out the same Samarium Barbie reaction, but with the addition of a nickel two catalyst as the additive weigh out nickel AK and add to a clean dry vial containing three milliliters of DGAs THF under argon at the nickel AK solution through a syringe to 10 milliliters of a freshly prepared solution of 0.1 molar sumer di iodide. Separately, in a clean, dry vial under argon, combine 110 microliters of iodine, 48 microliters of three penan, and two milliliters of dried THF. To make the substrate solution add the substrate solution dropwise to the sumerian di iodide nickel mixture.
Within 15 minutes of stirring, the blue color will dissipate to form a green color indicating the end of the reaction. After the reaction is complete, expose the solution to air to quench it. Upon stirring the color further changes to yellow, work up the reaction by adding three milliliters of 0.1 molar aqueous hydrochloric acid.
Add the solution to a separatory funnel and add five milliliters of dathyl ether. Wash the organic layer using the protocol described previously with an aqueous solution of sodium ths sulfate, water, and brine, and then dry over magnesium sulfate. Concentrate the solution on a rotary evaporator to obtain the Barbie or product.
The product can then be identified by GCMS and proton NMR illustrated. Here is the Sumerian Barbier reaction with no additives. The Sumerian mediated reaction takes 72 hours, yielding 69%of the desired product.
With the remaining being starting materials. With the addition of 10 or more equivalents of HMPA, the reaction is nearly quantitative and complete within a few minutes. With the addition of one mole percent nickel ak, the reaction is complete within 15 minutes with a 97%yield.
When HMPA is added to Samarium di iodide, the cos solvent displaces the coordinated THF to form samarium I two HMPA four. With the addition of even more HMPA, the iodide ions are displaced to the outer sphere. Mechanistic studies indicate that when HMPA is used in the Sumerian barbier reaction, the cos solvent also interacts with the AAL halide substrate forming a complex which elongates the carbon halide bond activating the species, making it more susceptible to reduction by Sumer.
Through this detailed understanding of the roles of HMPA, A mechanism for the Sumerian barbier reaction with HMPA was proposed. The ALK halide HMPA complex formed in a pree equilibrium step is reduced by samarium HMPA to form the radical in the rate determining step. The radical undergoes further reduction to form an organ samarium species, which couples with the carbon needle and upon protonation yields the final product.
In the case of nickel two, additive samarium di iodide initially reduces nickel two to nickel zero preferentially over reduction of either of the substrates based on kinetic and mechanistic studies. The following mechanism was proposed after reduction by samarium di iodide. The soluble nickel zero species inserts into the AAL halide bond forming an organ nickel species driven by the highly PHI nature of samarium three alation to form an organ.
Samarium intermediate releases nickel two back into the catalytic cycle. The sumer then couples with the carbon needle, and upon protonation forms the desired tertiary alcohol. It was also observed that nickel zero nanoparticles are formed through Sumerian mediated reduction of nickel two.
However, these particles were found to be inactive and the source of deactivation of the catalyst Following this procedure. The same barb, a product is obtained in both the cases. However, in most instances, the choice of different additives can provide control over the rate of reduction and the chemo or stereo selectivity of the reaction.
After watching this video, you should have a good understanding of how to generate samarium IDE solutions as well as techniques for overcoming the common pitfalls.
