Molybdocalixarene Structure Control via Rim Deprotonation. Synthesis, Characterization, and Crystal Structures of Calix[4]arene Mo(VI) Monooxo Complexes and Calix[4]arene Alkali Metal/Mo(VI) Dioxo Complexes

We report a series of calix[4]arene Mo(VI) dioxo complexes M2RC4MoO2 (M = alkali metal, R = H or But) that
were fully characterized by NMR, X-ray, IR, UV/vis, and elemental analysis. Molybdocalix[4]arene structures can
be controlled via lower rim deprotonation, groups at para positions of calix[4]arene, and alkali metal counterions.
Mono deprotonation at the lower rim leads to calix[4]arene Mo(VI) monooxo complexes RC4MoO (R = H, But, or
allyl), and full deprotonation gives rise to calix[4]arene Mo(VI) dioxo complexes. Structural studies indicate that
HC4 Mo(VI) dioxo complexes easily form polymeric structures via cation−π interaction and coordination between
different calixarene units. However, ButC4 Mo(VI) dioxo complexes tend to form dimers or tetramers due to steric
hindrance of the tert-butyl groups at para positions in calixarene. The structures of the reduced side products A
and C were determined by X-ray diffraction studies. The mechanism of RC4MoO formation from the reaction of
calixarene monoanions with MoO2Cl2 appears to include the addition of a calixarene −OH group across a MoO
bond.