Stabilization of a Monomethyl Orthomolybdate in the Binding Pocket of a Dinuclear Cobalt Complex

The ability of the dinuclear CoII complex [(LMe)CoII2(μ-Cl)]+ [1; (LMe)2- = 3,6,9,17,20,23-hexamethyl-3,6,9,17,20,23-hexaaza-29,30-dithiol-13,27-di-tert-butyltricyclo[23.3.111.15]triaconta-1(28),11,13,15(30),25,26-hexaene] to bind
tetrahedral oxoanions of the transition metal has been investigated. Two new complexes, [(LMe)CoII2(μ-MoO4)] (2)
and [(LMe)CoII2(μ-MoO3(OMe))]2[Mo4O10(OMe)6] (3), were prepared by substitution reactions of 1 with (n-Bu4N)2MoO4 in MeCN or with MoO3·2H2O/NEt3 in MeOH. Both compounds were characterized by X-ray crystallography.
The dioctahedral complex 2 features a μ1,3-bridging MoO42- unit, whereas the cation in 3 hosts an unprecedented
μ1,3-MoO3(OMe)- motif, demonstrating that four-coordinate molybdate esters can be stabilized in the binding pocket
of the bowl-shaped [(LMe)CoII2]2+ complex. The results of IR, UV/vis, and cyclic voltammetry measurements are
also reported.