The tris-benzimidazolium cage LH33+, in MeCN solution, in the presence of OH−, forms with CuI and AgI ions complexes of formula [MI(LH)]2+, in which each metal is linearly coordinated by two carbenes and one imidazolium N–H fragment remains intact. To achieve two-coordination, the two N-heterocyclic moieties of the cage make a saloon-door type motion, with a conformationally costless rotation of ca. 30° each. The two [MI(LH)]2+ complexes show high thermodynamic stability and are inert with respect to metal substitution, due to the mechanical constraints imposed by the ligating framework. Complexation with CuI and AgI with the reference unidentate carbene ligand Q, derived from the benzimidazolium precursor QH+, was studied for comparison. Both metals in MeCN form 1:1 and 1:2 complexes with the carbene ligand Q according to two stepwise equilibria. Q complexes of both metals are labile with respect to metal substitution and those of AgI are more stable than those of CuI. A significant cooperative effect has been observed with the formation of the [AgIQ2]+ complex.

The tris-benzimidazolium cage LH33+, in MeCN solution, in the presence of OH−, forms with CuI and AgI ions complexes of formula [MI(LH)]2+, in which each metal is linearly coordinated by two carbenes and one imidazolium N–H fragment remains intact. To achieve two-coordination, the two N-heterocyclic moieties of the cage make a saloon-door type motion, with a conformationally costless rotation of ca. 30° each. The two [MI(LH)]2+ complexes show high thermodynamic stability and are inert with respect to metal substitution, due to the mechanical constraints imposed by the ligating framework. Complexation with CuI and AgI with the reference unidentate carbene ligand Q, derived from the benzimidazolium precursor QH+, was studied for comparison. Both metals in MeCN form 1:1 and 1:2 complexes with the carbene ligand Q according to two stepwise equilibria. Q complexes of both metals are labile with respect to metal substitution and those of AgI are more stable than those of CuI. A significant cooperative effect has been observed with the formation of the [AgIQ2]+ complex.