We are undertaking a programme to carry out research into Group 4 metal catalysed reactions. Although titanium chemistry has concentrated in recent years on single site polyolefination catalysts containing cyclopentadienyl ligands it was apparent to us that there was considerable potential for development in the area of well-defined alkoxide catalysts of group 4 metals. Our work, which is being done in close collaboration with ICI Synetix, is focused the reaction of isocyanates with polyols to form polyurethanes. Currently, heavy p-block metals such as tin, lead and bismuth are the catalysts of choice for this and many other Lewis-acid catalysed polymerisations. We are investigating the mechanism of titanium-catalysed reactions and are also developing a new generation of reaction-specific catalysts based on a range of organic ligands that have not been used with organotitanates before. Initial results are encouraging: we have synthesised a range of potential catalysts (e.g., Figure 19 and Figure 20) and have begun to investigate their interaction with alcohols and isocyanates.
In collaboration with Prof. Ian Williams and ICI, we have been awarded a large grant entitled 'A Combined Synthetic and Computational Approach to Catalyst Design'. Within this programme we will investigate synthetic and computational (QM/MM) aspects of both early and late transition metal catalysts with a particular emphasis on improving selectivity and reactivity of Ti- and Pd-based systems.
Recent
Developments
We have recently investigated the use of related group 1, 2, 12 and 13
complexes as catalysts for the generation of other polyoxygenates (e.g.,
polylactones, polylactic acid, polycarbonates, etc.). Being both
environmentally and biologically benign, our catalysts offer considerable scope
for future development. For example, this area has been given considerable
impetus by current and proposed legislation outlawing the use of heavy p-block
metal catalysts: mercury has already been phased out and tin may soon follow.
Similarly, the introduction of, and recent increases in, landfill tax brings
issues relating to catalyst recycle and regeneration to the fore since it is
fast becoming uneconomic to landfill even ‘cheap’ catalysts. Also, as
the field of tissue engineering expands rapidly, there is a need for an
increasing range of well-defined biocompatible polymers, which can be supplied
by our biologically benign, selective single-site catalysts.