cobalt hydride complexes and catalysis

This Thesis describes the investigation of cobalt hydride complexes containing PN chelating ligands for cobalt-catalysed H2 evolution and CO2 reduction reactions. An overview of strategies for solar and electro-driven fuel production, the development of electrocatalysts for H2 evolution (HECs) by the natural hydrogenases, synthetic bio-inspired HECs and earth-abundant transition metal complexes are discussed in Chapter 1. Chapter 2 describes synthesis and characterisation of novel cobalt(III) hydride complexes supported by bis PN chelating diisopropylphosphino(2-methylpyridine) ligands: [CoIII(PN)2(H)(Cl)][PF6] and [CoIII(PN)2(H)(MeCN)][PF6]2 and related CoII complexes. Their electronic and redox properties as well as mechanistic electron transfers are also discussed. The mechanistic studies for H2 evolution catalysed by [CoII(PN)2(MeCN)][BF4]2, [CoIIIcis-(PN)2Cl2][PF6] as well as the corresponding hydride, [CoIII(PN)2(H)(MeCN)][PF6]2 and [CoIII(PN)2(H)(Cl)][PF6] via ECEC pathways are discussed in Chapter 3. The kinetic information of [CoII(PN)2(MeCN)][BF4]2 and [CoIII(PN)2(H)(MeCN)][PF6]2 as well as comparison of these two catalysts to previously reported HECs are detailed in the Chapter 3. Preliminary CV studies of CO2 reduction activity of [CoIII(PN)2(H)(Cl)][PF6] and [CoIIIcis-(PN)2Cl2][PF6] are also discussed. Chapter 4 describes synthesis and characterisation of the novel Co(II) complexes containing a tetradentate PNNP 2,9-bis(di-t-butylphosphino-methyl)-1,10-phenanthroline ligand as well as their electronic and redox properties. A chemical reduction of the [CoII(PNNP)Cl2] and [CoII(PNNP)MeCN][BF4]2 by LiMe or NaBEt3H suggested an activation mode of H-H bond breaking/making involving metal-ligand cooperation and aromatization–dearomatization processes. Furthermore, the H2 evolution and CO2 reaction activity of the [CoII(PNNP)Cl2] and the [CoII(PNNP)(MeCN)][BF4]2 is also discussed. Finally, Chapter 5 summarizes the important findings and suggests future work.