'Spring-loaded' system pops phosphorus into molecular rings
Date:
April 21, 2022
Source:
Massachusetts Institute of Technology
Summary:
Chemists have devised a new chemical reaction that allows them to
synthesize a phosphorus-containing ring, using a catalyst to add
phosphorus to simple organic compounds called alkenes.
FULL STORY ==========================================================================
MIT chemists have devised a new chemical reaction that allows them
to synthesize a phosphorus-containing ring, using a catalyst to add
phosphorus to simple organic compounds called alkenes.
========================================================================== Their reaction, which yields a ring containing two carbon atoms and one phosphorus atom, can be performed at normal temperature and pressure,
and makes use of a novel "spring-loaded" phosphorus-containing molecule
that supplies the phosphorus atom.
"This is a rare example of a discovery of a new catalytic reaction, and it opens up a real wealth of new opportunities to do chemistry enabled by a reaction that never existed before," says Christopher Cummins, the Henry Dreyfus Professor of Chemistry at MIT and the senior author of the study.
These phosphorus-containing rings could find uses as catalysts for other reactions, or as precursors for useful compounds such as pharmaceuticals, Cummins says.
MIT graduate student Martin-Louis Riu is the lead author of the
paper, published this week in the Journal of the American Chemical
Society. Former MIT research fellow Andre Eckhardt is also an author of
the study.
Creating a ring Organic compounds that contain double bonds between carbon atoms, also known as olefins or alkenes, are important precursors in many industrially useful chemical reactions. By breaking those carbon-carbon
bonds and adding new atoms or groups of atoms, researchers can create
a wide variety of new products.
==========================================================================
As one example, chemists have previously devised ways to convert a carbon- carbon double bond into a three-membered ring by adding either another
carbon atom, a nitrogen atom, or an oxygen atom. Such compounds can be
found in plastics, pharmaceuticals, textiles, and other useful products.
However, because phosphorus is heavier than carbon, nitrogen, or oxygen,
it has been difficult to find a way to incorporate it into olefins without using "brute force" methods that require harsh chemical conditions. The
MIT team wanted to come up with a way to perform this reaction under
mild conditions, using a catalyst to transfer a phosphinidene group --
a phosphorus atom bound to an organic chemical group -- to the olefin.
In order to achieve that, they needed a starting material that could act
as a source of phosphinidene, but such compounds did not exist because
direct analogues of those used for lighter elements such as carbon are
unstable with phosphorus.
In a 2019 paper, Cummins's lab developed one possible source, consisting
of phosphinidene attached to a molecule that contains several hydrocarbon rings.
Using this compound, they were able to synthesize a three-membered ring containing phosphorus, but the reaction required high temperatures and
only worked with certain types of olefins.
In their new paper, the MIT team used a different source of phosphorus
for the reaction -- a compound that Cummins' lab first synthesized in
2021. This molecule is a tetrahedron, a shape that inherently has a
great deal of energy "strain," much like a compressed spring, because
of the small bond angles between the four atoms that form the tetrahedron.
==========================================================================
This compound, called tri-tert-butylphosphatetrahedrane, has three
vertices consisting of carbon atoms attached to a chemical group called tert-butyl, and one vertex consisting of a phosphorus atom with an
unshared pair of electons.
Under the right conditions, this strained molecule can be broken apart
to release the phosphorus atom.
Efficient synthesis Using this spring-loaded molecule, the researchers
were able to use a nickel- containing catalyst to transfer phosphinidene
to olefins to create three- membered rings. This reaction can be done
at room temperature, with high yield of the desired product.
"All the stars aligned here in terms of us being able to synthesize a
highly strained precursor that leads to room temperature reactivity and
rapid catalysis," Cummins says.
The researchers now plan to further investigate the mechanism of how this reaction occurs, which they believe is dependent on phosphinidene being temporarily transferred to the nickel catalyst complex. The catalyst
then incorporates the phosphorus into the double bond of the olefin.
They also hope to explore the possibility of creating a variety of
new compounds that include the phosphorus-containing ring, and to
develop ways to control which of two possible mirror image versions
are synthesized. Once these phosphorus-containing rings are formed,
they can be opened up by adding additional molecules to create other
useful compounds. Potential applications for these kinds of products
include catalysts for other reactions, or components of pharmaceuticals
that contain phosphorus.
The research was funded by the National Science Foundation and a Feodor
Lynen Research Fellowship from the Alexander von Humboldt Foundation.
========================================================================== Story Source: Materials provided by
Massachusetts_Institute_of_Technology. Original written by Anne
Trafton. Note: Content may be edited for style and length.
========================================================================== Journal Reference:
1. Martin-Louis Y. Riu, Andre' K. Eckhardt, Christopher C. Cummins.
Reactions of Tri-tert-Butylphosphatetrahedrane as a Spring-Loaded
Phosphinidene Synthon Featuring Nickel-Catalyzed Transfer to
Unactivated Alkenes. Journal of the American Chemical Society,
2022; DOI: 10.1021/ jacs.2c02236 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/04/220421154146.htm
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