A novel organozinc initiator with a clear mechanistic signature for organic radical reactions has been developed.

Reactions of diethylzinc with TEMPO were investigated. Dropwise addition of 1 equiv of TEMPO to Et 2 Zn at −10 °C leads to the nitroxide complex EtZn(TEMPO) in high yield, whereas upon addition of 2 equiv of TEMPO the corresponding homoleptic nitroxide compound Zn(TEMPO) 2 is formed. Diffusion ordered NMR spectroscopy experiments revealed that both zinc nitroxide compounds exist in monomeric forms in solution, while single-crystal X-ray diffraction confirmed their dimeric structure in the solid state.

The subtle nature of reactivity of the free stable nitroxyl radical TEMPO towards tBu2Zn and Ph2Zn was explored in an uncommon comparison of wet, mechanochemical and slow-chemistry reactions.

Solution‐based syntheses are omnipresent in chemistry but are often associated with obvious disadvantages, and the search for new mild and green synthetic methods continues to be a hot topic. Here, comparative studies in four different reaction media were conducted, that is, the solid‐state mechano‐ and slow‐chemistry synthesis, melted phase, and solution protocols, and the impact of the employed solvent‐free solid‐state versus liquid‐phase synthetic approaches was highlighted on a pool of products. A moderately exothermic model reaction system was chosen based on bis(pentafluorophenyl)zinc, (C6F5)2Zn, and 2,2,6,6‐tetramethylpiperidinyl oxide (TEMPO) as a stable nitroxyl radical, anticipating that these reagents may offer a unique landscape for addressing kinetic and thermodynamic aspects of wet and solvent‐free solid‐state processes. In a toluene solution two distinct paramagnetic Lewis acid‐base adducts (C6F5)2Zn(η1‐TEMPO) (1) and (C6F5)2Zn(η1‐TEMPO)2 (2) equilibrated, but only 2 was affordable by crystallization. In turn, crystallization from the melt was the only method yielding single crystals of 1. Moreover, the solid‐state approaches were stoichiometry sensitive and allowed for the selective synthesis of both adducts by simple stoichiometric control over the substrates. Density functional theory (DFT) calculations were carried out to examine selected structural and thermodynamic features of the adducts 1 and 2. Compound 2 is a unique non‐redox active metal complex supported by two nitroxide radicals, and the magnetic studies revealed weak‐to‐moderate intramolecular antiferromagnetic interactions between the two coordinated TEMPO molecules.