Kilian Research
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Research
activities in our newly established group are centred on design and synthesis
of organophosphorus and Group 15 organoelement compounds. We synthesize new
compounds for various practical applications, such as spin labels. Novel
species are also of academic interest, we are very interested in exploration of
new bonding, structure and reactivity and in synthetic methodology development.
We also develop new (more efficient) syntheses of established compounds, such
as those used as plastic additives.
Our
typical synthetic project involves:
1.
Synthetic targets with specific
characteristics relevant to prospective use are proposed, often with the help
of computational chemistry.
2.
Synthetic
strategy towards the target compound is devised and tested. Sometimes several
synthetic approaches have to be tested to achieve the goal set out initially,
or the target has to be modified to become achievable.
3.
The desired
characteristics of the target compounds (sometimes predicted computationally)
are verified experimentally.
4.
The
characterization results are fed back into synthesis, suitable structural
modifications leading to improved characteristics are proposed and necessary
modifications are introduced to the synthetic pathway.
Unusual
(and therefore interesting) structural features, properties or reactivity crop
up sometimes during the experimental work. Exploitation of these unforeseen
results is an important part of (our) scientific activity.
The
four major areas of our research are:
Stable phosphorus centred radicals
Peri-substituted naphthalenes and related
systems
Green chemistry of white phosphorus
P-C bond forming reactions for tertiary phosphine
synthesis
Stable phosphorus centred radicals
Radicals
are usually observed as rather short-lived intermediates. In main group
chemistry they can be stabilised to the extent that they can even be isolated
in crystalline form. We have begun our investigations into stable phosphorus
centred radicals recently; of our particular interest are radicals with
potential to be used in spin labelling. Spin labels are artificial paramagnetic
probes introduced into the system (for example large biomolecules such as
membrane proteins) in order to make it ‘visible’ by Electron Paramagnetic
Spectroscopy (EPR), which is a particularly sensitive resonance spectroscopy
technique. New spin labels with favourable paramagnetic characteristics are
extremely desirable since they can improve the capabilities and scope of those
established, as well as several newly emerging and rapidly developing magnetic
resonance methods, such as DNP (Dynamic Nuclear Polarization, NMR enhancement
method), High Field and Pulsed EPR (used in long range distance measurements,
and dynamic processes investigations in biomolecules), as well as EPR Imaging
(medicinal imaging complementary e.g. to the more familiar NMR imaging - MRI).
As the need for new classes of spin labels is growing, our activities will be
even more strongly linked to spin label chemistry in the near future.
Phosphinyl radicals have large π-character of their SOMO
(Singly Occupied Molecular Orbital) and therefore large hyperfine anisotropy,
which makes them highly orientationally sensitive spin labels.
Phosphoranyl radicals can have extremely large hyperfine coupling,
which generates huge interest in their development as polarizing agents in
Dynamic Nuclear Polarization techniques.
Peri-substituted
naphthalenes and related systems
We
have a long-term interest in chemistry of peri-substituted (i.e.,
1,8-disubstituted) naphthalenes and related molecular frameworks. The special
geometry in these systems forces the
two substituents into a close proximity, making the attractive interaction
(i.e., bond) between them highly favourable as it minimises the steric strain.
This results in unusual reactivity, bonding, structure and properties.
Understanding the reactivity and development of synthetic methodology of
multiply functionalised organophosphorus molecules is important for practical
applications of these and related compounds (for example in catalysis). Unusual
bonding, structure and properties are often observed in peri-substituted
naphthalenes, and are of fundamental interest.
Green chemistry of white phosphorus
Many
phosphorus chemicals (bulk and fine) are made from white phosphorus, but
indirectly via phosphorus trichloride. Manufacture of PCl3 requires
chlorine gas, which is highly toxic and corrosive, possesses high environmental
risk and is ‘energy expensive’. Halogenation of white phosphorus to PCl3
serves essentially as a means of reactivity moderating and often no halogen is
retained in the resulting products. Therefore, it is highly desirable to search
for other means of moderating the reactivity of white phosphorus in order to
achieve energy and atom efficient transformations into high value chemicals,
without the formation of halide waste. Ideally the new reactivity moderators
replacing halogenation will be inexpensive, non-toxic, highly specific and
highly efficient (therefore only catalytic amounts will be needed).
P-C bond forming
reactions for tertiary phosphine synthesis
P-C bond forming reactions are
central to syntheses of tertiary phosphines, which in turn are essential
components of many transition metal complexes used as catalysts in many organic
transformations. Established P-C bond forming strategies require specifically
activated organic substrates to achieve the required reactivity when connecting
them to the phosphorus atom regiospecifically. The aim of our research in this
area is to develop new synthetic routes to make a variety of tertiary
phosphines from non-activated substrates, mainly aromates.
