Homogeneous and Heterogeneous Transition Metal Catalysis: from Bimetallic to Earth Abundant Metal Catalysts

This thesis describes the design, preparation and use of homogeneous bimetallic and monometallic Rh and Ir catalysts as well as hybrid bimetallic and monometallic Rh heterogeneous catalysts immobilised onto solid carbon supports. In addition, Earth abundant transition metal catalysts were developed as catalysts for a range of organic transformations. Two homoditopic bis[bis(pyrazol-1-yl)methane] ligands employing a [2.2]paracyclophane scaffold were synthesised, using ps-para- and ps-ortho- substitution patterns. Bimetallic Rh(I), Rh(III), Ir(I) and Ir(III) complexes of these ligands were prepared. Analogous monometallic Rh(I) and Ir(I) complexes were also synthesised and all complexes were fully characterised, with the solid-state structure of selected complexes determined using XRD analysis. The application of Ir(I) [2.2]paracyclophane based bimetallic and monometallic complexes as catalysts for the intermolecular hydroamination reactions of amines with alkynes to produce imines was investigated, and bimetallic enhancements were observed. The origin of the bimetallic hydroamination catalytic enhancement was determined using NMR spectroscopy, using isotopically labelled metal complexes and reaction substrates. Ir(I) bimetallic and monometallic complexes were also explored as catalysts for the reduction of imines using hydrosilylation reactions. A two-step, one pot protocol was developed using an Ir(I) bimetallic complex for C-N and subsequent N-Si bond formation reactions. Heterogeneous hybrid Rh(I) bimetallic and monometallic catalysts were prepared through the immobilisation of bis[bis(pyrazol-1-yl)methane] pro-ligands onto carbon supports (carbon black and reduced graphene oxide) using diazonium chemistry, followed by Rh(I) complexation. These catalysts were applied to a range of dihydroalkoxylation and hydroamination reactions, with bimetallic enhancements observed. Recycling studies showed the reusability of these catalysts, with low metal leaching. Earth abundant transition metals were tested for hydroamination reactions of aniline with alkynes. The use of Fe(III) with a weakly coordinating anion unexpectedly resulted in the formation of 1,2-dihydroquinolines. Mechanistic investigations using NMR spectroscopy performed using potential reaction intermediates and deuterium labelled substrates revealed the likely existence of two simultaneous reaction pathways. Overall, this thesis reports improved catalyst efficiency through the use of homogeneous and recyclable hybrid heterogeneous precious metal catalysts, and Earth abundant metal catalysts, for a range of C-N, N-Si, C-O and C-C bond formation reactions