AbstractSynthetic polymers play an increasingly dominant role in almost every aspect of 21st century human life. With notable exceptions, polymers containing significant quantities of elements other than carbon remain a subject of academic curiosity, yet already show potential as useful materials in commodity and speciality applications. Central to this elemental disparity is the requirement for a robust and versatile toolkit of efficient element-element bond forming reactions. Herein, various aspects pertaining to the use of alkaline-earth mediated dehydrocoupling as a tool for inorganic polymer synthesis are investigated in detail.
Initially focussing upon the well-established alkaline-earth mediated dehydrocoupling of silanes and amines, a series of soluble ferrocene-containing metallo-polycarbosilazanes and model molecular compounds were synthesised. Whilst monomer choice was found to be a decisive factor in the ability to yield well-defined polymeric structures, this approach proved to be an effective method to access previously unexplored metallopolymers. Although wider application was limited by the hydrolytic sensitivity of backbone Si-N bonds, the polymers displayed well-behaved reversible electrochemical behaviour and were found to be promising precursors to magnetic ceramic materials, which themselves were subjected to extensive characterisation.
The scope of alkaline-earth mediated cross-metathesis was subsequently expanded to the dehydrocoupling of silanes and alcohols. Besides providing access to hydrolytically robust ferrocene-containing metallo-polysilylethers, extensive investigations into the scope and mechanism of catalysis provided insight into an intricate and complex reaction manifold. Factors such as ionic radius, catalyst and substrate concentration, and active species nuclearity were found to exert a profound influence on mechanism and activity.
The construction of polymer chains composed entirely of other main-group elements provides fascinating materials which often exhibit totally different properties to their carbon-analogues. Since they produce polymer chains formally isoelectronic to polyolefins, organostannanes and phosphine-boranes are monomers of interest, yet their dehydrogenative polymerisation is dominated by transition-metal catalysis. The final portion of this work sought to address this issue by conducting a preliminary investigation into the chemistry of calcium- and magnesium stannyl and phosphidoborane complexes. Structural, spectroscopic, and computational investigations provided valuable insight into virtually unexplored chemistry combining the alkaline-earths and heavier p-block elements.
|Date of Award||19 Feb 2020|
|Sponsors||Engineering and Physical Sciences Research Council|
|Supervisor||Michael Whittlesey (Supervisor) & Michael Hill (Supervisor)|