Synthesising P-C Bonds Using Dehydrochlorination

This project develops catalytic dehydrochlorination chemistry that has been recently achieved in the Webster lab.
This is entirely unprecedented and offers a unique opportunity to generate P-P bonds using inexpensive, easily
handled and commercially available chlorophosphines.
The reaction of HPPh2 and ClPPh2 in the presence of an iron catalyst takes place within seconds at room
temperature. The chemistry is facile even with simple iron salts, but catalyst design is likely to prove instrumental
when we move beyond simple arylphosphine-arylchlorophosphine coupling. Investigation into such a rapid
transformation will be possible using flow instrumentation, particularly ICPMS in flow in place in Bath, and will give a
comprehensive real-time picture under the reaction conditions. Study of stoichiometric interactions is likely to be
limited by paramagnetism particularly because, on coordination to iron, there is complete loss of phosphorus signals
in the 31P NMR making investigation of the coordination environment at iron or the catalyst resting state problematic.
A dedicated ReactIR work station in place in the lab will allow us to determine rates of reaction more effectively for
highly paramagnetic systems and also monitor the loss or growth of key stretching frequencies both stoichiometrically
and during catalysis.
Following this, intramolecular dehydrochlorination will give facile access to phosphaalkynes, an immensely exciting
class of compounds with untapped potential for use across a wide range of applications. Having only previously been
prepared under harsh conditions, or by transient formation through masked reagents, we expect to be able to carry
out this transformation under very mild conditions. By monitoring the change in vibrational frequencies of P-Cl, P=C
and P---C bonds, ReactIR will inform on reactive intermediates and resting states, particularly if iron salts and
propagating paramagnetic species dominate the system: it will provide the flexibility an d rapid results needed to
move the study forward.
P---C compounds will be prepared and used in catalytic hydrofunctionalisation for the synthesis of multiple-P
containing products, main group-P compounds (for use as chelating ligands and Frustrated Lewis Pair chemistry)
and cationic iron complexes can be implemented for cyclotrimerisations, overall generating completely novel
phosphines using catalysis.
Dehydrochlorination to generate phosphaalkenes will give a library of novel polymerisation monomers. Ionic
polymerisation techniques will be used to generate polyphosphines or UV activation to form cyclobutane-type
coordination polymers for use in gas/solvent adsorption methodologies.
Finally, phosphaalkynes and phosphaalkenes, although explored as ligands in stoichiometric studies, are not known
as reagents in catalytic small molecule synthesis: we seek to change our synthetic outlook by developing new facile
methods for their preparation which will at last allow their implementation as reagents in synthesis.
This project finds its relevancy to the EPSRC from the potential development of new iron-based catalysts for use in
main group transformations. These catalysts will be designed to facilitate sustainable reactions, which may lead to
novel phosphorous containing compounds.