Bis(amidophenolate)-supported Pnictogen Complexes: Redox Activity, Cooperativity and Electromerism

by Simon Bernhard Hugo Karnbrock
Doctoral thesis
Date of Examination:2025-09-16
Date of issue:2025-11-26
Advisor:Prof. Dr. Manuel Alcarazo
Referee:Prof. Dr. Manuel Alcarazo
Referee:Prof. Dr. Dietmar Stalke
Referee:Prof. Dr. Konrad Koszinowski
Referee:Prof. Dr. Johannes C. L. Walker
Referee:Prof. Dr. Anna Krawczuk
Referee:Dr. Daniel Janßen-Müller
Persistent Address: http://dx.doi.org/10.53846/goediss-11654

 

 

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Abstract

English

This thesis describes the synthesis, characterization and reactivity of pnictogen compounds derived from the tetradentate, redox-active bis(amidophenolate) ligand, N,N′-bis(3,5-di-tert-butyl-2-phenoxy)-1,2-phenylenediamide. Initially, the synthesis of the complete series of 10-Pn-4 (Pn: P, As, Sb, Bi) pnictoranide anions is reported. Coordination of these anions to the cyclopentadienyliron(II) dicarbonyl fragment delivers the corresponding 10-Pn-5 complexes for P, As and Sb, while in the case of Bi an electron redistribution takes place: The corresponding 12-Bi-5 compound was isolated featuring a two-electron oxidized bis(amidophenolate) scaffold. This case of Lewis acid-induced electromerism was experimentally confirmed through X-ray diffraction analyses as well as IR, UV-Vis and Mössbauer spectroscopy. Furthermore, an electrophilic chlorophosphorane derived from the same ligand was synthesized. Substitution of the chloride with 1,2-diphenylhydrazine results in its organocatalytic disproportionation into azobenzene and aniline. Mechanistic studies, spectroscopic analyses and DFT calculations suggest that this unprecedented reactivity mode for P(V)-centers is induced by the high electrophilicity at the P(V)-center combined with the ability of the bis(amidophenolate) ligand to act as an electron reservoir. The same chlorophosphorane reacts with ketones and aldehydes in a fundamentally different manner. A phosphorus-ligand cooperative pathway gives rise to iminio phosphoramidate species. The amphiphilic nature of these products enables the selective reductive coupling of aldehydes to ethers under catalytic conditions. Finally, the synthesis and structural characterization of a slightly distorted square pyramidal arsenium cation is described. Spectroscopic, crystallographic, and computational evidence indicate that coordination of typical Lewis bases to the As(III)-center induces its oxidation to As(V) with concomitant reduction of the supporting, redox-active bis(amidophenolate) ligand. That reaction is reversible and represents a well-defined example of base-induced electromerism in an As-complex. Single electron reduction of the same As(III) species generates an As(III)/As(V) heterodimer by redox-induced electron transfer.
Keywords: pnictogens; main group; redox-active ligand; element-ligand cooperativity; electromerism; valence tautomerism; catalysis
 
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