Presents synthetic routes to phosphoryl ligands which have potential utility in nuclear waste remediation.

1. Synthesis of of Cis-1,2-bis(diphenylphosphino)ethylene Sulfide
Selenide
Abstract
The 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.
Introduction
The 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
Conclusion
To 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.
Key observations for the synthesis of benzyldiphenylphosphine:
1. Mild bubbling, and visible consumption of most lithium metal within one
hour with formation
2. 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
monoselenide
1. 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 60⁰C for one hour.
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 Oxide
After 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.
Results
The 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.