Electron Rich Metallo Nitrene Complexes For Nitrogen Transfer

by Till Schmidt-Räntsch
Doctoral thesis
Date of Examination:2024-12-10
Date of issue:2025-01-10
Advisor:Prof. Dr. Sven Schneider
Referee:Prof. Dr. Sven Schneider
Referee:Prof. Dr. Inke Siewert
Referee:Prof. Dr. Peter Burger
Persistent Address: http://dx.doi.org/10.53846/goediss-10981

 

 

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Abstract

English

The advent of C–N bond formation by catalytic C–H amination had a huge impact on the synthesis of nitrogen-containing compounds, in academia as well as industry. In contrast to nitrogen-group transfer, complementary nitrogen-atom transfer is heavily underdeveloped. This can be attributed to the high stability of most reported (early) transition metal nitrides, while the more reactive late transition metal nitrides are too reactive for isolation or even characterization. In this work, rare group 10 transition metal nitrides (metallo-nitrenes) are synthesized and their electronic nature is analyzed by spectroscopic and computational methods. The reactivity of Pd and Pt metallonitrene complexes towards C–H and C=C bonds is investigated, revealing a unique nucleophilic behavior of the transient nitrene. The Pd metallonitrene is capable of catalytic C-H bond amidation, being the first example for catalytic nitrogen-atom transfer. Reactivity of the Pt metallo-nitrene with styrene leads to a rare case of C=C bond cleavage, leading to C=N bond formation by imination. Mechanistic studies, most importantly EPR, suggest a radical mechanism, which is initiated by catalytic amounts of PtI. Transition metal nitrides are an important class of compounds, especially with regard to fundamental structure and bonding. They can be synthesized readily by photoinduced N2 loss from the parent azide complex, however, the elementary primary events that facilitate N2 elimination after electronic excitation remain largely unknown. The here reported pincer complex of a Pt azide serves as an ideal probe for transient absorption IR spec-troscopy, revealing the individual steps from electronic excitation to N2 loss. A triplet azide, produced by triplet sensitization from the strongly absorbing pincer backbone, seems to be the key species leading to N2 loss. These findings might serve as a design princi-ple, which allows highly efficient photoinduced N2 loss of organic or inorganic azides on the triplet surface.
Keywords: Coordination Chemistry; Nitrene; Pincer Complex; Palladium; Platinum; Nitrogen Atom Transfer; Azide
 
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