NHC-Stabilized Inverse Crown Ethers Featuring the μ4-Oxo [Mg4O] Core

Compared to crown ethers with functions to capture metal cation, inverse crown ethers (ICEs) with a similar cavity architecture have the alternating polarity of cationic metal ring and encapsulated ion to construct the skeleton. Here we introduce a new tridentate aryloxide-N-heterocyclic carbene ligand to stabilize mu(4)-oxo [Mg4O] cores in ICEs, which open up a path towards synthetic methodology for ICEs. The reaction of N-Heterocyclic carbene (NHC) lithium complex (L)Li-2(L-1) (1; L={1-C(NDippCH(2)CH(2)N)}(2)(CH2)(2)PhO-, Dipp=2,6-Pr-i(2)-C6H3; L-1=(SiMe3)(2)N-) with MgBr2 afforded a mixture of (L)Mg2Br3 (2), (L)(2)Mg4OBr4 (3) and (L)Mg4OBr5(THF)(2) (4), via the salt metathesis. Symmetric 3 and unsymmetric 4 including the same mu(4)-Oxo [Mg4O] unit possess ICEs character, where O2- atoms lie in the centroid binding to all four Mg2+ centers.

Automated summary

Inverse crown ethers (ICEs) have alternating polarity of cationic metal ring and encapsulated ion, with a new tridentate aryloxide-N-heterocyclic carbene ligand introduced to stabilize mu(4)-oxo [Mg4O] cores in ICEs. The reaction with MgBr2 resulted in formation of (L)Mg2Br3, (L)(2)Mg4OBr4, and (L)Mg4OBr5(THF)(2), which all possess ICEs character with mu(4)-Oxo [Mg4O] unit.