Book excerpt: "A cobalt analogue of Cp*Co(PMe3)Me(OTf) (Cp* = 1, 2, 3, 4, 5 - pentamethylcyclopenta-dienyl, OTf = OSO2CF3), in Chapter 2, was attempted to be synthesized and studied for electrophilic C-H bond activation. Three new cobalt complexes Cp*Co(PMe3)(Me)2, Cp*Co(PMe3)(OTf)2 and Cp*Co(PMe3)(Me)(I) were synthesized. The 1H NMR spectrum showed a new material formed after mixing Cp*Co(PMe3)(Me)2 and Cp*Co(PMe3)(OTf)2 in 1:1 ratio. In Chapter 3, five carboxylate ligated iridium complexes (dmPhebox)Ir(O2CR)2(H2O) (R = -CH3(known compound), -CH2CH3, -CMe3, - CH2C6H5, -CH=CMe2) were designed and synthesized to understand the carboxylate ligand effects on the reactivity of the complex for alkane dehydrogenation. Results from the kinetic study showed that different R groups of the carboxylate iridium complexes can affect the reactivity with octane in the ??H elimination step. The rate constants for octane formation with different carboxylate ligands follow the order R = -CH=CMe2 > -CMe3 > -CH2CH3 > -CH3 > -CH2C6H5. In contrast, there is no significant effect of carboxylate ligand on the rate of the C-H activation step at 160 ʻC. These experimental results support the findings in the previously reported density functional theory (DFT) study of the (dmPhebox)Ir complex in alkane C-H activation. In Chapter 4,5 and 6, hydrogen transformation during the dehydrogenation and hydrogenation of N-heterocycles with a cobalt pincer catalyst, hydrogenation of alkenes with Fe(II) precursors, and hydrogenation of alcohols and dehydrogenation of ketones with a Cp*Rh(III) catalyst were investigated. The results of the acceptorless, reversible dehydrogenation and hydrogenation of N-heterocycles suggests a bifunctional dehydrogenation pathway and a non-bifunctional hydrogenation mechanism. The iron catalysts described in Chapter 5 operate via a metal-ligand cooperative pathway via a stepwise hydride transfer and then proton transfer mechanism. The Cp*Rh(III) catalysts in Chapter 6 decompose upon heating to give nanoparticles."--Pages xi-xii.