The syntheses and X-ray crystal structures of dinuclear μ-azido and μ-nitrido bridged iridium complexes bearing the pyridine, diimine ligand (PDI) are reported. Their electronic structures and formal oxidation states of the metal centers are analyzed by theoretical and experimental methods, revealing the non-innocence of the PDI and nitrido ligands.

Si–H activation in triethyl- and triarylsilanes by a square-planar pyridine-diimine iridium complex with a terminal nitrido unit leads to the corresponding silyl amido complexes, which were unambiguously characterized by X-ray crystallography. Based on detailed combined kinetic and theoretical studies (DFT), direct addition of the Si–H bond to the iridium nitrido unit is proposed. The electronic propensities of the transition states for the Si–H activation were probed with a Hammett series of para-substituted triarylsilanes HSi(C6H5)2(4-C6H4-X). Based on the combination of experimental and theoretical studies, two independent pathways for this process are proposed, which point toward an ambiphilic propensity of the nitrido unit. Alternative pathways and the charge transfer in the transition states were also investigated. Furthermore, the barriers for the related H–H and C–H activation processes in dihydrogen and methane were analyzed.

The bonding situation and energetics of the N–O bond in a series of amine-N-oxides, Phx(CH3)3−xN–O, where x = 0–3, were analyzed experimentally and theoretically. There is a notable nearly linear decrease of the N–O bond dissociation energies (BDEs) for this series with an increasing number of phenyl groupsx. This was investigated experimentally by X-ray high angle multipole refinement techniques in combination with subsequent topological analysis of the electron density for the representative (CH3)2PhN–O, 2, and complementary theoretical calculations at the DFT and multireference CASSCF and MR-perturbation theory (MCQDPT2) levels. Both the theoretical and experimental results unambiguously revealed a polar covalent σ-bond for the N–O bond with an essentially identical bonding situation for all amine-N-oxides studied. This apparent disparity between the bonding situation and the trend of BDEs is attributed to the large differences of the relaxation energies of the corresponding amines Phx(CH3)3−xN, (x = 0–3), respectively, the required preparation energies (ΔEprep) for the reverse N–O bond forming process. The detailed theoretical analysis of the amines allowed us to trace the trend of larger values of ΔEprep for a higher number of phenyl groupsx to an increase of n(N) → π*(C–C) delocalization interactions.

Intramolecular activation processes of vulnerable ligand C–H bonds frequently limit the thermal stability and accessibility of late transition metal complexes with terminal metal nitrido units. In this study chloro substitution of the 2,6-ketimine N-aryl substituents (2,6-C6H3R2, R = Cl) of the pyridine, diimine ligand is probed to increase the stability of square-planar iridium nitrido compounds. The thermal stability of iridium azido precursor and nitrido compounds was studied by a combination of thermoanalytical methods (DTG/MS and DSC) and were compared to the results for the related complexes with 2,6-dialkyl substituted N-aryl groups (R = Me, iPr). The investigations were complemented by DFT calculations, which allowed us to unravel details of the thermal decomposition pathways and provided mechanistic insights of further conversion steps and fluctional processes. The DTG/MS and DSC measurements revealed two different types of thermolysis pathways for the azido compounds. For the complexes with R = Cl and iPr substituents, two well-separated exothermic processes were observed. The first moderately exothermic loss of N2 is followed by a second, strongly exothermic transformation. This contrasts the experimental results for the compound with 2,6-dimethyl substituents (R = Me), where both steps proceed concurrently in the same temperature range. The separation of the two thermal steps in the 2,6-dichloro substituted derivative allowed us to develop a protocol for the isolation of the highly insoluble nitrido complex, which was characterized by UV/vis, IR-spectroscopy and elemental analysis. Its constitution was further confirmed by reaction with silanes, which gave the corresponding silyl amido complexes.

Coordinative polymerization of fluorinated olefins is still a challenging task. We analyzed the catalytic properties of diimido chromium VI compounds computationally by density functional methods. It was found that reactivity predictions depend strongly on the density functional chosen for the computations. Therefore, DFT calculations were calibrated to high level wave function theory calculations. Then geometrical parameters, which can be tuned by a ligand, were scanned to elucidate their influence on the catalytic activity. Having arrived at an optimal parameter set, we randomly assembled chromium complexes from a fragments database and automatically checked for their activities. This led to the proposal of three exemplary catalyst candidates.

The syntheses and X-ray crystal structures of dinuclear μ-azido and μ-nitrido bridged iridium complexes bearing the pyridine, diimine ligand (PDI) are reported. Their electronic structures and formal oxidation states of the metal centers are analyzed by theoretical and experimental methods, revealing the non-innocence of the PDI and nitrido ligands.

The bonding situation and energetics of the N–O bond in a series of amine-N-oxides, Phx(CH3)3−xN–O, where x = 0–3, were analyzed experimentally and theoretically. There is a notable nearly linear decrease of the N–O bond dissociation energies (BDEs) for this series with an increasing number of phenyl groupsx. This was investigated experimentally by X-ray high angle multipole refinement techniques in combination with subsequent topological analysis of the electron density for the representative (CH3)2PhN–O, 2, and complementary theoretical calculations at the DFT and multireference CASSCF and MR-perturbation theory (MCQDPT2) levels. Both the theoretical and experimental results unambiguously revealed a polar covalent σ-bond for the N–O bond with an essentially identical bonding situation for all amine-N-oxides studied. This apparent disparity between the bonding situation and the trend of BDEs is attributed to the large differences of the relaxation energies of the corresponding amines Phx(CH3)3−xN, (x = 0–3), respectively, the required preparation energies (ΔEprep) for the reverse N–O bond forming process. The detailed theoretical analysis of the amines allowed us to trace the trend of larger values of ΔEprep for a higher number of phenyl groupsx to an increase of n(N) → π*(C–C) delocalization interactions.

Intramolecular activation processes of vulnerable ligand C–H bonds frequently limit the thermal stability and accessibility of late transition metal complexes with terminal metal nitrido units. In this study chloro substitution of the 2,6-ketimine N-aryl substituents (2,6-C6H3R2, R = Cl) of the pyridine, diimine ligand is probed to increase the stability of square-planar iridium nitrido compounds. The thermal stability of iridium azido precursor and nitrido compounds was studied by a combination of thermoanalytical methods (DTG/MS and DSC) and were compared to the results for the related complexes with 2,6-dialkyl substituted N-aryl groups (R = Me, iPr). The investigations were complemented by DFT calculations, which allowed us to unravel details of the thermal decomposition pathways and provided mechanistic insights of further conversion steps and fluctional processes. The DTG/MS and DSC measurements revealed two different types of thermolysis pathways for the azido compounds. For the complexes with R = Cl and iPr substituents, two well-separated exothermic processes were observed. The first moderately exothermic loss of N2 is followed by a second, strongly exothermic transformation. This contrasts the experimental results for the compound with 2,6-dimethyl substituents (R = Me), where both steps proceed concurrently in the same temperature range. The separation of the two thermal steps in the 2,6-dichloro substituted derivative allowed us to develop a protocol for the isolation of the highly insoluble nitrido complex, which was characterized by UV/vis, IR-spectroscopy and elemental analysis. Its constitution was further confirmed by reaction with silanes, which gave the corresponding silyl amido complexes.