Synthesis of of Cis-1,2-bis(diphenylphosphino)ethylene Sulfide Selenide

AbstractThe Advanced Synthesis course (CHM 452) at

Grand Valley State University (GVSU) explored the preparation and reaction selectivity of unsymmetric dichalcogenide phosphoryl ligands in various solvents, in addition to derivatizing triarylphosphines using alkali metal. Research currently being done at GVSU on actinide separations provides promising results with symmetrical bidentate ligands, however the synthesis of unsymmetrical ligands was previously unexplored. Successful synthesis of the monosubstituted selenide was completed [31P NMR (CDCl3) δ: 22.2ppm (d) and -27.5ppm (d)]. The inability to form the monosubstituded sulfide in various solvent systems indicated a fast kinetic reaction to the disubstituted phosphine. Successful synthesis of benzyl(diphenyl)phosphine [31P NMR (CDCl3) δ:-8.7ppm (t)], was completed through a Grignard-like reaction in order for the phosphine to perform a nucleophilic attack on various alkyl and aryl halides.

IntroductionThe difficulty with the separation of the

spent nuclear fuel is separation of trivalent actinides from the lanthanides produced as FPs. Their similar oxidation states, chemical properties, and ionic radii, cause the separation to be very difficult. Most industrially effective actinide-lanthanide separations take advantage of the actinides’ stronger ability to interact with soft donor atoms (e.g. Chloride, Nitrogen, Phosphorus, or Sulfur). The formation of metal complexes can occur when organic ligands are used during the separation process. The process can be further optimized by performing the extraction from aqueous media, often being of high acidity. The problem of selective extraction of actinides has been an actively pursued are of chemical research for over 60 years, with the first separation of uranium and plutonium done by the chemists during the Manhattan Project in the 1940s4. The most widely used process for the removal of plutonium and uranium around the world is the Plutonium Uranium Recovery by Extraction (PUREX). This process includes the extractant, tributyl phosphate (shown below) in a hydrocarbon solvent.

Synthesis of Benzyl(diphenyl)phosphine

ConclusionTo summarize, lithium metal has been shown to be an efficient

reagent for the cleavage of triphenylphosphine needed in order to produce a vast array of different coordinating species. In order to successfully produce the reduced form of the benzyl(diphenyl)phosphine, exposure to air and water must be minimized. Because of this, further preparation procedures must be investigated in order to avoid the production of benzyl(diphenyl)phosphine oxide. Although useful, the oxide form was an undesired by-product and attempts to reduce said oxide failed.

In addition, elemental selenium and sublimed sulfur have displayed some peculiar properties upon reaction with the diaryl vinylene. The vinyl group provided additional complications into the synthesis of the hetero-substituted ligand, including isomerization (cis-trans) and unique side reactions leading to homo-disubstituted side products. Further investigation into the preparation are still underway, but there are high hopes for the apparent coordination of actinide metals.

Synthesis of Hetero-substituted Bidentate Ligands and Triaryl Phosphines: An Attempt to Further Research Nuclear Waste Remediation

Jeremy Cunningham, Nick Bostater, John Bender, Department of Chemistry, Grand Valley State University, Allendale, MI 49401

Key observations for the synthesis of benzyldiphenylphosphine:1. Mild bubbling, and visible consumption of most lithium metal within one

hour with formation2. Dark red color solution indicates the precense of phenyllithium.3. After the addition of tert-butyl chloride, bubbling occurred indicating the

formation of vaporous byproducts.4. Following the consumption of phenylithium, indicated by the disappearence

of the dark color, benzyl chloride was added to the reaction vessel. The solution appeared greenish yellow with undissolved white solid in, indicating the presence of lithium chloride.

Key Observations for the synthesis of cis-1,2-bis(diphenylphosphine)ethene

monoselenide1. Following the addition of one

equivalent elemental selenium to the cis-dppe starting material, the yellow reaction was momentarily stirred in benzene before 20mins of sonication.

2. After adding half of an equivalent selenium, the mixture was allowed to sit for 24hrs leaving behind a crystalline yellow solid.

Key Observations for the synthesis of Cis-1,2-bis(diphenylphosphino)ethylene Sulfide Selenide

1. Following the recrystallization of the monoselenide (cis-dppeSe1), one equivalent of sublimed sulfur was added and the two were allowed to stir momentarily before sitting for 7 hours.

2. Three successive columns were ran in hopes of separation. Various, exotic solvent systems were used but little separation occurred.

3. Complete separation of the hetero-substituted ligand proved was inconclusive as both di-substituted products were found in the reaction mixture. The three compounds were found to co-crystallize after solvent evaporation at room temperature.

①In order to cleave on of the arylphosphine bonds, two equivalents of solid lithium was added to a stirring mixture of triphenylphosphine in tetrahydrofuran (THF) and heated at 60 C for one hour.⁰

②After most of the lithium was consumed, one equivalent of tert-butyl chloride was added to the brown mixture in order to remove the phenyl lithium by-product. Bubbling of the vaporous products were observed in the absence of heat.

③ When the bubbling subsided, one equivalent of benzyl chloride was added to the red mixture. Acting as a sort of Grignard reagent, lithium diphenylphosphide forced the production of insoluble lithium chloride salt.

Spectral Data for benzyl(diphenyl)phosphine and derivatives

Spectra 2. Benzyldiphenylphosphine Selenide The reaction between benzyldiphenylphosphine and selenium was very fast, upon NMR analysis a shift of the 31P NMR peak from benzyldiphenylphosphine to the new product peak indicating that the desired product was formed. This shows a rapid kinetic drive toward the product. The peak shift appears to show satellites from selenium’s ½ spin, and there is no substantial starting material peak remaining.

Spectra 1. Benzyldiphenylphosphine OxideAfter analyzing crude reaction product from the lithium reaction, oxide was observed (δ=30.6ppm) after work-up of the free phosphine (δ=-8.7ppm). Starting material can also be seen (31PNMR δ=-4.3ppm).

References

Aguiar, A.M.; Daigle, D., JACS, 1964, 5354.

Grim, S.O., Walton, E.D., “Unsymmetrical Bis-Phosphorus Ligands. 12. Synthesis and Nuclear Magnetic Resonance Studies of Some Derivatives of Bis(diphenylphosphino)methane”, Inorg. Chem., 1980, 1982.

Nandi, P.; Dye, J.L.; Bentley, P.; Jackson, J.E., Org Lett, 2009, 1689.

ResultsThe reaction to form benzyl(diphenyl)phosphine appears successful from 31PNMR analysis,

with a shift from -4.321 to -8.694ppm indicating that the desired product was made. The overall reaction efficiency was rather high, as there is a small peak for starting PPh3 when compared to the product peak. Phosphine oxide (δ=30.5ppm) can be present in small yields however after completing the organic-aqueous separation. Isolation of this product was reacted with elemental selenium. The reaction was very fast, with a shift of the 31PNMR peak from benzyldiphenylphosphine to the new product peak (δ=35.4ppm) indicating the desired product was formed within minutes. After adding the selenium to the reaction vessel the mixture was immediately entered into the NMR and analyzed, showing a rapid kinetic drive toward the product.

After running the reaction on the cis-vinylene in multiple solvents, benzene was observed to have enough kinetic control of the reaction so that the mono-substituted selenium product could be isolated. The mono-substituted sulfur product, however, could not be isolated due to a strong preference to form the disubstituted sulfur compound in all solvents used. Spectral analysis of the monoselenide indicated one substituted phosphine and one free phosphine at 22.2ppm and -27.5ppm respectively. This provided ground for further work into heterosubstituted ligands, such as the selenium and sulfur substituted compound.

The hetero-substituted ligand was made by reacting the mono-selenide with one equivalent of sublimed sulfur. The doublet peak values shifted down field after all free phosphine was consumed as seen in the 31PNMR spectra.