Factors controlling the structure of alkylzinc amidinates: on the role of N -substituents.

Despite various applications of alkylzinc complexes supported by N , N -bidentate ligands in chemistry and materials science, the corresponding organozinc amidinates still represent an insufficiently explored area. To gain a more in-depth understanding of factors controlling the structure and stability of alkylzinc amidinates, we selected benzamidinate and N , N '-diphenylformamidinate ligands as model N , N '-unsubstituted and N , N '-diaryl substituted ligands, respectively, to systematically modify the secondary coordination sphere of the Zn center. A series of new alkylzinc amidinates has been synthesized and their molecular structures identified in both the solid state (single-crystal X-ray crystallography) and solution (NMR and FTIR spectroscopy). The results indicate that [RZnL] x -type amidinate moieties are essentially unstable and tend to undergo Schlenk equilibria-mediated ligand scrambling leading to more thermodynamically stable non-stoichiometric [R 2 Zn 3 L 4 ]- and [R 3 Zn 4 L 5 ]-type complexes. This process is significantly influenced by the secondary coordination sphere noncovalent interactions as well as the steric hindrance provided by both zinc-bounded alkyl groups and the N -substituents.