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Metal-Nitrogen Multiple Bonds with Square-Planar Group 9 Transition Metal PNP Pincer Complexes

dc.contributor.advisorSchneider, Sven Prof. Dr.
dc.contributor.authorScheibel, Markus
dc.publisherNiedersächsische Staats- und Universitätsbibliothek Göttingende
dc.titleMetal-Nitrogen Multiple Bonds with Square-Planar Group 9 Transition Metal PNP Pincer Complexesde
dc.contributor.refereeSchneider, Sven Prof. Dr.
dc.description.abstractengNitrogen is ubiquitous in synthetic and biosynthetic products as an important building block for molecular architecture and functionality. Bimolecular dinitrogen (N2) is its common appearance in nature and is characterized by a strong N–N triple bond and a high kinetic barrier for further conversion. Ammonia as the chemically more accessible nitrogen source is produced under harsh reaction conditions via the Haber-Bosch-process, consuming 1.4% of the global energy. Activation of dinitrogen under ambient conditions is an important goal for industrial and academic research. Cleavage of N2 into electron poor (d0-d2) terminal nitrido complexes has been demonstrated using early to mid transition metal complexes, and the conversion of nitrides into amines or ammonia was reported with electron rich late transition metal nitrides. However, only three examples of square-planar nitrido complexes with a d4 electronic configuration were reported so far. This thesis focuses on the synthesis of square-planar platforms to investigate on electronic structure-reactivity relationships of electron rich terminal nitrido complexes of iridium and rhodium. Template synthesis of a new fully dehydrogenated PNP pincer ligand allowed for the isolation of an unprecedented series of IrI/II/III complexes in identical coordination environment. Whereas the IrI PNP chloro complex exhibited interesting reactivity towards C–H and small molecule activation, the d6 low-spin configuration of square-planar IrIII provided an ideal platform for investigations on multiple bonded ligands on Ir. Oxidative cleavage of azide allowed for the isolation of thermally stable iridium terminal nitrido complex. Reactivity studies revealed electrophilic behavior of the nitrido ligand and allowed for the structural characterization of a full series of chalcogenonitrosyl complexes of iridium. One electron reduction of cationic iridium nitride enabled  the spectroscopic characterization (NMR, IR, EPR, ENDOR) of open-shell nitrido complex with an electronic structure of one unpaired electron localized in an Ir–N π-antibonding molecular orbital. Kinetic and computational investigations revealed a pronounced nitrogen centered radical character to be crucial for selective formation of N2, suggesting the nitridyl mesomeric formulation as key structure for nitrido coupling and hence, as intermediate in N2 cleavage reaction following the principle of microscopic reversibility. Transfer of reactivity to rhodium revealed a similar electronic structure for the first example of a terminal nitrido complex of rhodium based on spectroscopic investigations (IR, EPR), localizing an even higher spin density on the nitride. The high selectivity for N–N coupling reaction of open-shell nitrides with respect to nitrene insertion or hydrogen atom transfer (HAT) reactivity was rationalized based on investigations on the bond dissociation free energies of parent iridium amido and imido complexes. Interconversions of iridium nitride with amide revealed a low average N–H bond dissociation free energy of parent iridium amido complex. Investigations on the formation of parent iridium imido complex resulted in disproportionation and is understood in terms of a weaker N–H bond in the case of the imide. de
dc.contributor.coRefereeMeyer, Franc Prof. Dr.
dc.contributor.thirdRefereeMeyer, Karsten Prof. Dr.
dc.subject.engterminal nitrido complexesde
dc.subject.engparent iridium amidede
dc.subject.engopen-shell nitridede
dc.subject.engnitride couplingde
dc.subject.engnitrogen activationde
dc.subject.engnitrosyl complexesde
dc.subject.engbond dissociation free energyde
dc.subject.engpincer ligandsde
dc.affiliation.instituteFakultät für Chemiede
dc.subject.gokfullChemie  (PPN62138352X)de

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