Highly Electron-Rich β-Diketiminato Systems: Synthesis and Coordination Chemistry of Amino-Functionalized 'N-nacnac' Ligands

摘要

The synthesis of a class of electron-rich aminofunctionalized b-diketiminato (N-nacnac) ligands is reported, with two synthetic methodologies having been developed for systems bearing backbone NMe_2 or NEt_2 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 CH_2 group. Direct metalation with lithium, magnesium, or aluminium alkyls allows access to the respective metal complexes through deprotonation of the methylene function; in each case X-ray structures are consistent with a delocalized iminoamide ligand description. Transmetalation using lithium Nnacnac complexes is then 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 NR_2 groups appears to be constrained by the inability of the amino group to achieve effective conjugation with the N_2C_3 heterocycle. More obvious divergence from established structural norms is observed for complexes of the harder Yb~(II) ion, with azaallyl/imino and even azaallyl/NMe_2 coordination modes being demonstrated by X-ray crystallography.