DETAILS
OF RESEARCH
Synthetic
Chemistry (Inorganic, Organometallic, Organic) for
Functional Molecules
Applications:
· Homogeneous Catalysis (strategic ligand design, ferrocenes, redox-active catalysis)
· Supramolecular
Chemistry (metal-alkynyl architecture, ‘molecular wires’)
· Materials Science (electronic
OLED/magnetic/optical materials)
· Biomedical Imaging (PET labelled
compounds, MRI contrast agents, quantum dots)
We
have a diverse, multi-faceted research programme of both academic and
industrial relevance featuring applied synthetic chemistry (crossing
traditional inorganic and organic boundaries).
Elegant synthetic strategies have been developed, dovetailed with
utilisation of the new compounds for applications within catalysis and materials
science. Topics include:-
· Metallocene
chemistry, featuring new chiral and hemilabile, donor-substituted ferrocene
ligands and redox-acitve
transition metal pre-catalysts
Formation of novel hemilabile ligands with neutral
and/or charged N/O, S/P, S/S and P/O substituents. Interesting and unusual metal
coordination chemistry observed and complexes tested for homogeneous catalytic
processes i.e. olefin and lactide polymerisation, carbonylation,
hydrogenation and Heck and Suzuki coupling reactions.
Redox-active catalysis - In a proof of concept study (see above –
JACS, 2006), we have established for the first time that redox
switches may be used to attenuate the activity of single-site polymerization
catalysts. Thus, a titanium-based lactide
polymerization initiator supported by a ferrocenyl-substituted
salen ligand exhibits a
substantially higher rate of propagation than its oxidized dicationic
ferrocenium analogue. The reversibility of the redox event is demonstrated by treatment with chemical redox reagents.
(Key
references: J. Am. Chem. Soc, 2006, 128, 7410; Organometallics, 2006, 25, 1932; Dalton Trans.,
2006, 3134; Chem. Soc. Rev., 2004, 33, 313).
· Organometallic
polymers, transition metal - alkynyl chemistry
('Molecular wires')
Mono-, oligo- and poly-nuclear metal-alkynyls
synthesised and characterised for 2-D
and 3-D supramolecular systems and formation of 'molecular wires'. Interest in studying
the electronic interactions within conjugated aromatic-alkynyl
materials and gain understanding of the control of band-gap and conduction in
these materials, properties probed by
electrochemistry, absorption and emission spectroscopy and theoretical
calculations.
(Key
references: Angew. Chem. Int. Ed., 2003, 42, 2586; Organometallics, 2006, 25, 2525; J. Organomet. Chem., 2006, 691, 1389).
· Electroluminescent Materials - Lanthanide and Transition Metal Containing
Complexes for Electro- and Photo-luminescent Materials (OLED devices)
Synthesis of
metal-organic materials designed to possess particular properties (i.e. solubility, volatility,
electroluminescence, phosphorescence) that are important in new commercially
relevant devices. Near-IR and triplet
state emitting materials.
In
a key experiment (JACS, 2005), dramatic increases in the luminescent lifetime
of the Er3+ ion in a molecular complex have been observed by
chelating the rare-earth ion with a per-fluorinated imidodiphosphinate
sensitizing ligand, ‘F-tpip’. For solution, powder and evaporated thin
films of Er(F-tpip)3
the average lifetimes of the 1530 nm emission band range between 150 –
220 μs, corresponding to a maximum 50-fold
increase relative to the non-fluorinated analogue, Er(tpip)3.
These are the longest reported lifetimes for the Er3+ ion a
simple organic chelate. These remarkable improvements in luminescence
efficiency and excited state lifetime represent a significant step forward in
the design and fabrication of near-infrared (NIR) emitting molecular devices
for communications, sensing and analytical detection.
(Key
references: J. Am.
Chem. Soc., 2005, 127, 524; J.
Am. Chem. Soc., 2004, 126, 5223).
· Biomedical Imaging - Applications in
PET Imaging and MRI/Optical Contrast Agents
We have recently
embarked on projects sponsored by GlaxoSmithKline
(GSK) to develop new chemistry and compounds featuring 11CO/11CO2 incorporation for PET imaging. We are using transition metal-catalysed
processes for the formation of 11C-labelled amides, esters and thioesters and form new transition metal macrocyclic CO/CO2-containing compounds, and
apply the syntheses on a microfluidic scale via
'lab-on-a-chip' technology. For the
first time a microstructured device (see figure
below) has been used to perform a gas-liquid carbonylation
reaction - featuring the Pd-catalysed cross-coupling reaction of arylhalides with benzylamine and
CO to rapidly form a range of secondary amides (Chem. Comm. 2006).
We are also interesting in Novel 11Carbon-Labelled Molecules for
Non-Specific Binding for Positron Emission Tomography (PET). Current research is
underway to understand the propensity of a PET-labelled
drug to bind to a lipid membrane, and how this may interfere or enhance a
molecule's ability to bind to and ultimately interact with the
targeted enzyme or receptor. The ultimate objective is to design
molecules that can target receptors and enzymes very specifically by
providing insight into the way molecules cross biological membranes. This
will greatly aid the development of better PET diagnostic imaging
agents, the design of new drugs and improve the efficiency of
the whole process of pharmaceutical drug development. The figures below show 11C-PET scans,
illustrating increasing non-specific binding of drug molecules in the brain.
Other
related topics include new transition metal and lanthanide MRI contrast agents, featuring ligand
design, and incorporation of specific metals such as Gd,
Mn and Fe.
And the synthesis of novel and biocompatible quantum dots. This project aims
to diminish cytotoxicity of quantum dots with the use
of biomaterials. These biomaterials will be either of natural origin or GRAS
status (generally regarded as safe). Biocompatible polymers
(and/or their modifications) will be assembled/conjugated
on novel Quantum Dots to encapsulate them for minimal leakage. The pictures on the right show cells labelled
with quantum dots, under bright field and fluorescence.
(Key
references: Chem. Commun., 2006,
546; Chem. Soc. Rev., 2006, 35, 557).
(last updated