Aminotroponiminates: Impact of the NO2 Functional Group on Coordination, Isomerisation, and Backbone Substitution

Aminotroponiminate (ATI) ligands are a versatile class of redox‐active and potentially cooperative ligands with a rich coordination chemistry that have consequently found a wide range of applications in synthesis and catalysis. While backbone substitution of these ligands has been investigated in some detail, the impact of electron‐withdrawing groups on the coordination chemistry and reactivity of ATIs has been little investigated. We report here Li, Na, and K salts of an ATI ligand with a nitro‐substituent in the backbone. It is demonstrated that the NO2 group actively contributes to the coordination chemistry of these complexes, effectively competing with the N,N‐binding pocket as a coordination site. This results in an unprecedented E/Z isomerisation of an ATI imino group and culminates in the isolation of the first “naked” (i. e., without directional bonding to a metal atom) ATI anion. Reactions of sodium ATIs with silver(I) and tritylium salts gave the first N,N‐coordinated silver ATI complexes and unprecedented backbone substitution reactions. Analytical techniques applied in this work include multinuclear (VT‐)NMR spectroscopy, single‐crystal X‐ray diffraction analysis, and DFT calculations. Unforeseen aspects of ATI chemistry: The impact of a nitro substituent in the backbone of the aminotroponiminate (ATI) ligand on the coordination chemistry and reactivity of alkali metal (Li−K) complexes has been investigated. This includes the first examples of i) an isolable free ATI anion, ii) E/Z imine isomerisations of ATI species and iii) N,N‐coordinated silver ATIs.