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

Abstract

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 SnII 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 YbII ion, with azaallyl/imino and even azaallyl/NMe2 coordination modes being demonstrated by X-ray crystallography.