A Case Study on the Desired Selectivity in Solid‐State Mechano‐ and Slow‐Chemistry, Melt, and Solution Methodologies

• Published in: ChemSusChem Vol. 14; no. 18; pp. 3887 - 3894
• Main Authors: Budny‐Godlewski, Krzysztof, Leszczyński, Michał K., Tulewicz, Adam, Justyniak, Iwona, Pinkowicz, Dawid, Sieklucka, Barbara, Kruczała, Krzysztof, Sojka, Zbigniew, Lewiński, Janusz
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 20.09.2021
• Subjects: Adducts; Antiferromagnetism; Chemical synthesis; Comparative studies; Coordination compounds; Crystallization; Density functional theory; Exothermic reactions; Lewis acid; mechanochemistry; melted phase; organometallics; Reagents; Selectivity; Single crystals; slow chemistry; Solvents; Stoichiometry; Substrates; TEMPO; Toluene
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.202101269

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. Four directions: The impact of four different synthesis approaches on a pool of products is presented for a model (C6F5)2Zn/2,2,6,6‐tetramethylpiperidinyl oxide (TEMPO) reaction system. For the first time reactions in solution, mechanochemistry, slow‐chemistry, and melted‐phase reactions are collated in this comprehensive study of model reaction system.