Ligand control in nuclearity of Zn complexes supported by formamidinates

Using N,N′-diarylformamidinate (DArF) ligands containing different substituents of varying steric properties as the supporting ligands, four Zn complexes of atypical structural geometries were successfully synthesized and fully characterized. Detailed structural comparisons indicated steric hindrance of the ligands was a crucial factor in governing the geometry and nuclearity of the Zn products. DArFs with low steric hindrance to the metal centers produced two trinuclear Zn clusters (1 and 2) where all ligands were in non-symmetric coordination modes in both solid state and solution phase. DArFs with relatively bulky substituents led to the formation of bimetallic complexes 3 and 4 in a pseudo-paddlewheel geometry where each two Zn cores were held together by two DArFs parallel to each other. This study, together with the monozinc complex {HC(NDipp)2}2Zn (Dipp = 2,6-diisopropylphenyl) in the literature, indicated that an increase in the steric demands of the ligands led to a decrease in the nuclearity of the Zn–formamidinate complexes. All product complexes were relatively thermally robust, but air and moisture sensitive. A tetranuclear cluster with an interstitial oxide was obtained when a small amount of oxygen content was present during the synthesis.

It was found that the steric properties of N,N′-diarylformamidinates controlled the geometry and nuclearity of the Zn products. Increase in steric demands of the ligands decreased the complex nuclearity from three to two. Ligands in the trinuclear clusters resided in non-symmetric coordination modes in both solid state and solution phase.Figure optionsDownload as PowerPoint slide