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 [R2Zn3L4]- and [R3Zn4L5]-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.

Automated summary

Organozinc amidinates, specifically alkylzinc complexes supported by N,N-bidentate ligands, have been extensively studied in various fields. However, the corresponding organozinc amidinates are still poorly explored. This study aims to investigate the factors influencing the structure and stability of alkylzinc amidinates by modifying the Zn center's secondary coordination sphere. Through synthesis and characterization techniques, it was found that the [RZnL](x)-type amidinate moieties are unstable and tend to undergo ligand scrambling, forming more thermodynamically stable non-stoichiometric complexes.