Abstract
Several new bimetallic and trimetallic complexes containing the [Y-(COT)(2)](-) unit in different coordination environments are synthesized and fully characterized using X-ray crystallography and NMR spectroscopy. These complexes include [K([2.2.2]-cryptand)]-[Y-(COT)(2)] (1), [K-(18-crown-6)-(THF)]-[Y-(COT)(2)] (2), [Y(2)K(2)(COT)(4)(THF)(4)] (3), and [YKCa-(COT)(3)(THF)(3)] (4). In the presence of secondary ligands, bimetallic ionic pairs that comprise a [Y-(COT)(2)](-) sandwich and a solvent-wrapped K(+) ion are formed in 1 and 2. In contrast, 3 represents a bimetallic tetradecker oligomer with two [Y-(COT)(2)](-) units bridged by a K(+) ion and a terminal [K-(THF)(4)](+) moiety. Complex 4 is a heterotrimetallic triple-decker with an axial arrangement of three metal centers to form [Y-(COT)(2)K-(COT)-Ca-(THF)(3)]. Structural analysis shows the Y-COT(centroid) distances in the [Y-(COT)(2)](-) sandwich are equidistant (1.884(6) Å) in 1 but become asymmetric in 2-4 (1.857(3)-1.952(3) Å), reflecting additional external coordination. The two COT rings are parallel in 1 and become increasingly tilted from 0.8 to 27.5° in 2-4, respectively. Multinuclear NMR spectroscopy measurements reveal the solution behavior of the sandwich and heterometallic multidecker COT-based products. The observed NMR spectroscopic trends corroborate with weak interactions between the [Y-(COT)(2)](-) unit and cationic moieties persisting in solutions of 2-4.