Ammonia Solvation vs Aqueous Solvation of Samarium Diiodide. A Theoretical and Experimental Approach to Understanding Bond Activation Upon Coordination to Sm(II).

Coordination-induced desolvation or ligand displacement by cosolvents and additives is a key feature responsible for the reactivity of Sm(II)-based reagent systems. High-affinity proton donor cosolvents such as water and glycols also demonstrate coordination-induced bond weakening of the O-H bond, facilitating reduction of a broad range of substrates. In the present work, the coordination of ammonia to SmI was examined using Born-Oppenheimer molecular dynamics simulations and mechanistic studies, and the SmI-ammonia system is compared to the SmI-water system. The coordination number and reactivity of the SmI-ammonia solvent system were found to be similar to those of SmI-water but exhibited an order of magnitude greater rate of arene reduction by SmI-ammonia than by SmI-water at the same concentrations of cosolvent. In addition, upon coordination of ammonia to SmI, the Sm(II)-ammonia solvate demonstrates one of the largest degrees of N-H bond weakening reported in the literature compared to known low-valent transition metal ammonia complexes.