This work describes the synthesis, characterization and catalytic application of a new class of welldefined iron based PNP-pincer complexes. In particular, iron hydride complexes of the type [Fe(PNP)(H)(CO)(L)] have been prepared and tested as catalysts for the hydrogenative reduction of C-O double bonds. The metal center in these complexes is stabilized by PNP-pincer ligands that are based on 2,6-diaminopyridine scaffolds. In contrast to related pyridine derived pincer systems, these ligands allow for a modification of the linker¿s substituents, which might have a decisive impact on the reactivity of the corresponding complexes. In the first part of this thesis is focused on the hydrogenative reduction of carbonyl compounds has been investigated. ^Complexes [Fe(PNPH-iPr)(H)(CO)(L)] containing labile co-ligands (L = Br , CH3CN, BH4 ) and N-H spacers are efficient catalysts for the hydrogenation of both ketones and aldehydes, while those containing inert ligands (L = pyridine, PMe3, SCN , CO) are catalytically inactive. Interestingly, complex [Fe(PNPMe-iPr)(H)(CO)(Br)], featuring N-Me spacers, is an efficiently catalyzes the hydrogenation of aldehydes, but was found to be unreactive towards ketones. Based on detailed experimental and computational studies, it could be shown that the hydrogenation of ketones takes place via an inner-sphere reaction mechanism in which the catalytically active species is formed upon deprotonation of one N-H group. The second type of catalysts instead proceed via a different intermediate, since they are not capable undergoing this type of metal ligand cooperation. ^Further studies on this catalyst revealed an outer-sphere mechanism, in which an iron(II) dihydride was identified to be the catalytically active species. This intermediate could even be isolated, structurally characterized and independently employed in catalytic hydrogenation reaction. This catalyst appeared to be highly active and productive achieving turnover numbers of up to 80.000 and TOFs of more than 20.000 h-1. Moreover, a remarkable degree of chemoselectivity could be reached, as other reducible functionalities including ketones, conjugated C-C double bonds, esters, epoxides and nitrosyl groups remain unaffected in course of the reaction. The second part of this work is concerned with the application of these complexes as catalysts in the reversible hydrogenation/dehydrogenation of carbon dioxide or formic acid, which is considered to serve as a potential hydrogen storage technology for future energy supply. ^Both complexes, those bearing N-H as well as those bearing N-Me linker substituents, were found to promote the catalytic hydrogenation of CO2 and NaHCO3 to formates, reaching quantitative yields and high TONs even under mild reaction conditions. NMR and DFT studies highlighted the role of dihydrido and hydrido formate complexes in catalysis, strongly resembling the mechanism previously proposed for the selective hydrogenation of aldehydes. Moreover, the described catalysts are also capable for the reverse dehydrogenation of formic acid to yield carbon dioxide and molecular hydrogen. Formic acid decomposition takes place in presence of a stoichiometric amount of triethyl amine reaching turnover numbers of more than 10.000.