Highly electron rich β-diketiminato systems: synthesis and coordination chemistry of amino functionalized "N-nacnac" ligands

The synthesis of a class of electron-rich amino-functionalized β-diketiminato (N-nacnac) ligands is reported, with two synthetic methodologies having been developed for systems bearing backbone NMe₂ or NEt₂ groups and a range of N-bound aryl substituents. In contrast to their (Nacnac)H counterparts, the structures of the protio-ligands feature the bis(imine) tautomer and a backbone CH₂ group. Direct metallation with lithium, magnesium or aluminium alkyls allows access to the respective metal complexes via deprotonation of the methylene function; in each case X-ray structures are consistent with a delocalized imino-amide ligand description. Trans-metallation using lithium N-nacnac complexes has then been exploited to access p and f-block metal complexes which allow for like-for-like benchmarking of the N-nacnac ligand family against their more familiar Nacnac counterparts. In the case of Sn^II the degree of electronic perturbation effected by introduction of the backbone NR₂ groups appears to be constrained by the inability of the amino group to achieve effective conjugation with the N₂C₃ heterocycle. More obvious divergence from established structural norms are observed for complexes of the larger, harder Yb^II ion, with azaallyl/imino and even azaallyl/NMe₂ coordination modes being demonstrated by X-ray crystallography.