Tacticity, Regio and Stereoregularity

This chapter focus on the polypropylene tacticity. The stereoregularity and regioregularity of the processes catalyzed by heterogeneous and homogeneous Ziegler-Natta catalysts are discussed. The amazing variety of molecular architectures available for polypropylene-based materials are summarized together with the catalytic mechanisms for tacticity control. The main techniques applied for the determination of PP tacticity are reported as well as the outstanding development of new catalyst systems able to achieve unprecedented PP microstructures

Activation of Small Molecules by U(III) Cyclooctatetraene and Pentalene Complexes

The low-valent complexes of uranium (i.e. those containing U(III) centres) are characterised as reactive, highly reducing species that can effect novel, and potentially useful, transformations of small molecules. In this chapter we review one particular class of these compounds - those supported by cyclooctatetraene and pentalene ligands - whose reduction chemistry has recently demonstrated novel and unexpected results, including the cyclooligomerisation of CO. The syntheses and structures of these compounds are presented, and their reactivity towards a variety of small molecules is examined and reviewed. The reactivity towards carbon monoxide is discussed in reference to the historical development of obtaining oxocarbons from CO