Coordination chemistry of alkali metals in a modified β-diketiminate ligand scaffold

Abstract

β-diketiminate (or NacNac) ligands are a widely used ligand class in the stabilisation of metal complexes across the periodic table, in part due to the ease of variability of the ligand steric and electronic effects either at the β-carbon atom or the N-Ar group. Functionalisation of the γ-carbon position is not typically observed however and examples of such complexes are scarce in the literature. Herein, we report on the synthesis and characterisation of alkali metal NacNac complexes which contain such γ-carbon functionalisation in the form of a methyl group. Deprotonation of the β-diketimine proligand ^Me3DipNacNacH 1 (^Me3DipNacNacH = (CH₃)C(C(CH₃)NDip)₂H, Dip = 2,6-iPr₂-C₆H₃) by various alkali metal bases yielded the corresponding alkali metal complexes ^Me3DipNacNacAM (where AM = Li 2, Na 3, K 4, Rb 5, Cs 6) which have been fully characterised by ¹H and ¹³C{¹H} NMR spectroscopy, while 3 and 4 have been structurally characterised by single-crystal X-ray diffraction. The solid-state structures obtained illustrate the varied range of coordination modes accessible to such group 1 metal complexes.