Introducing NacNac-Like Bis(4,6-isopropylbenzoxazol-2-yl)methanide in s-Block Metal Coordination

Within this work, the field of bulky methanides in metal coordination is exceeded by the synthesis of the versatile and promising bis(4,6-isopropylbenzoxazol-2-yl)methane (7) ligand platform. As an enhancement in this class of ligands, isopropyl (iPr) substituents as steric-demanding groups have been successfully introduced in proximity to the coordination pocket, mimicking the shielding abilities of the ubiquitous NacNac ligand scaffold to improve the steric protection of a coordinated s-block metal cation. A percent buried volume (% V_bur) calculation as well as an electronic structure analysis shades light onto the shielding and electronic abilities of the ligand in comparison to other selected methanides and diketiminates. Upon deprotonation with a variety of different group 1 and 2 metalation agents, a row of novel s-block metal complexes of the parent deprotonated monoanionic ligand 7 was obtained and structurally, as well as spectroscopically, characterized. In particular, in this context, the alkali-metal precursor complexes [Li(THF)₂{(4,6-iPr-NCOC₆H₂)₂CH}] (8) and [K{μ-(4,6-iPr-NCOC₆H₂)₂CH}]_∞ (9) as well as the alkaline-earth-metal compounds [MgCl(THF)₂{(4,6-iPr-NCOC₆H₂)₂CH}] (10) and [M(THF)_n{(4,6-iPr-NCOC₆H₂)₂CH}₂] [M = Mg, n = 0 (11); M = Ca, n = 1 (12); M = Sr, n = 1 (13); M = Ba, n = 1 (14)] were successfully synthesized. Especially, the latter four exhibit interesting trends in the solid state as well as in solution within the metal series.