Synthesis of Terminal Transition Metal Pnictide Complexes by Activation of Small Molecules

by Josh Abbenseth
Doctoral thesis
Date of Examination:2019-07-08
Date of issue:2019-08-13
Advisor:Prof. Dr. Sven Schneider
Referee:Prof. Dr. Sven Schneider
Referee:Prof. Dr. Franc Meyer
Referee:Prof. Dr. Robert Wolf
Persistent Address: http://dx.doi.org/10.53846/goediss-7599

 

 

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Abstract

English

Coordination compounds involving metal-nitrogen bonds are a well-developed class of organometallic chemistry. In contrast, the chemistry of the heavier analogues of nitrogen, e.g. phosphorus and arsenic is far less explored. This thesis describes the synthesis and characterization of suitable rhenium and osmium PNP pincer compounds to serve as starting materials for further conversion towards heavy transition metal pnicogen complexes. A square-planar Os(II) PNP pincer complex is reported which features a unique electronic structure and serves as a convenient starting material to synthesize square-planar Os(IV) nitride complexes in unusual coordination spheres, as well as an open-shell phosphanyl radical complex. The conversion towards the corresponding phosphinidene complex is elucidated by calorimetric measurement and thermodynamical square-schemes. Furthermore, an unprecedented Os(IV) chloro-phosphinidene complex can be synthesized and its electronic structure is analyzed by quantum chemical calculations. In the case of rhenium, the synthesis of terminal phosphide and arsenide complexes is reported, enabled by linkage-isomerism of a coordinated pyrazol-pyridine ligand to allow for selective conversion. The electronic structure and reactivity of the terminal pnictide complexes is thoroughly analyzed. One-electron oxidation leads to pnicogen atom transfer to give donor-acceptor stabilized diphosphorus and diarsenic complexes which are characterized by QTAIM calculations. The terminal phosphide complex can be further converted towards low-molecular phosphorus oxide complexes by oxygen atom transfer. Finally, mechanistic aspects of dinitrogen splitting by molybdenum PNP pincer complexes are investigated by several spectroscopic techniques, including X-ray absorption spectroscopy.
Keywords: Coordination Chemistry; Terminal Pnictide Complexes; Proton-Coupled Electron Transfer; Dinitrogen Splitting; Phosphanyl Radicals; Phosphinidenes; Osmium Pincer Complexes; Rhenium Pincer Complexes; Molybdenum Pincer Complexes
 
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