A novel strategy towards the catalytic hydroamination of alkenes: Exploiting geometrically constrained phosphorus(III) species for the activation of ammonia
Final Report Abstract
Within the Walter Benjamin Programme, a project was undertaken to explore the N–H bond cleavage of ammonia using geometrically distorted phosphorus compounds. The objective was to gain insights into the potential of this class of substances for transition metal free hydroamination catalysis. Initially, various platforms were modeled using DFT calculations to identify suitable candidates for a reversible and slightly exergonic N–H bond cleavage. Subsequently, a phosphine derivative of an asymmetric tridentate NNS ligand was pinpointed as a promising target. The corresponding phosphine was successfully synthesized on a large scale in the laboratory and exhibited the desired reactivity. For the first time, the N–H bond of ammonia could be cleaved with complete thermal reversibility in a closed system. These results provided valuable insights for the future utilization of ammonia in metal-free catalysis. Following this, within the framework of the Walter Benjamin Programme and the return fellowship, preliminary steps were taken towards establishing an independent research group. A novel, rigid, acridane derived NNN pincer ligand was developed. By incorporating phosphorus, the reactivity of the resulting T-shaped phosphine, ligated by the chemically inert NNN pincer ligand, was investigated. The planarized phosphine displayed electrophilic reactivity towards protic and hydridic substrates, activating them via P-ligand cooperativity under retention of the P-oxidation state. Furthermore, various P(V) compounds were generated by reacting the phosphine with azides and chalcogens, causing the geometry of the NNN ligand to shift towards a "bowl-shape." The employed ligand was also redox-active, capable of being oxidized by up to two electrons. This property was harnessed to reduce oxygen by four electrons using Ta(V) complexes – marking the first instance of complete O2 cleavage by a single transition metal complex, with the required electrons solely originating from the ligand. Towards the end of the funding period, initial outcomes were achieved in terms of synthesizing additional NNN pincer ligands. This advancement aims to enable the future utilization of planarized main-group elements in diverse oxidation and charge states for activating small molecules and as novel ligands for transition metals. Building upon these findings, the potential of main-group and transition-metal compounds ligated with the developed NNN pincer ligands will be further explored in the context of metalfree hydroelementation catalysis and catalytic ammonia oxidation.
Publications
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Recent developments in the chemistry of non-trigonal pnictogen pincer compounds: from bonding to catalysis. Chemical Science, 11(36), 9728-9740.
Abbenseth, Josh & Goicoechea, Jose M.
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Thermoneutral N−H Bond Activation of Ammonia by a Geometrically Constrained Phosphine. Angewandte Chemie International Edition, 60(44), 23625-23629.
Abbenseth, Josh; Townrow, Oliver P. E. & Goicoechea, Jose M.
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Dioxygen Splitting by a Tantalum(V) Complex Ligated by a Rigid, Redox Non‐Innocent Pincer Ligand**. Chemistry – A European Journal, 29(5).
Underhill, Jack; Yang, Eric S.; Schmidt‐Räntsch, Till; Myers, William K.; Goicoechea, Jose M. & Abbenseth, Josh
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Reactivity of a Strictly T‐Shaped Phosphine Ligated by an Acridane Derived NNN Pincer Ligand. Chemistry – A European Journal, 29(39).
King, Aaron J.; Abbenseth, Josh & Goicoechea, Jose M.
