Room-temperature photosynthesis of Zn(i) compounds with high air stability

Abstract

Zn(I) compounds are important in fundamental chemistry and material science fields such as catalysis. However, previously described preparation methods require high temperature, anaerobic conditions, or the presence of external media, and most Zn(I) compounds are unstable in air. The current work revealed the ability of two binuclear Zn(II) coordination compounds, [Zn₂(MAA)₄(bipy)]_n (1, MAA = methacrylate, bipy = bipyridine; a reported compound) and [Zn₂(PA)₄(bipy)]_n (2, PA = propionate; a new compound), with similar metalloviologen functional motifs, to generate Zn(I) and radicals upon being illuminated at room temperature in air. Photoinduced Zn(I) products of 1 and 2 were stable in air for over 22 days and less than 1 day, respectively. The higher air stability of the photoproduct of 1 was attributed to the relatively large interannular dihedral angle and thus low delocalization of electrons in the bipy ligand. Conversely, compound 2 showed a higher Zn(I) generation yield than did 1, owing to the stronger electron-donating ability of PA than of MAA and shorter electron transfer paths in 2. These findings suggested a new facile method for preparing Zn(I) compounds with high air stability, helping to expand the family of Zn(I) materials.