Versatility of cyclooctatetraenyl ligands in rare earth metal complexes of the [M2(COT)3(THF)2] (M = Y and La) type

Two new organometallic cyclooctatetraenyl complexes of the type [M-2(COT)(3)(THF)(2)] (M = Y and La) have been prepared, using optimized synthetic procedures, and fully characterized by X-ray diffraction analysis, IR and H-1 NMR spectroscopies. The structures can be represented as formed by the double-decker [M(COT)(2)](-) anion with an asymmetrically bound cationic [M(COT)(THF)(2)](+) unit. The COT rings in the anionic sandwich are not equidistant from the metal with the M-COTcentroid distances measuring at 1.991(5) angstrom and 2.074(5) angstrom for [Y(COT)(2)](-) vs. 2.045(4) angstrom and 2.154(5) angstrom for [La(COT)(2)](-). The sandwich fragments are eta(2)-coordinated to the second metal center with the average M-C distances of 2.837(4) angstrom and 2.879(5) angstrom for yttrium and lanthanum complexes, respectively. The M-COTcentroid distances in the cationic unit are 1.962(4) angstrom for the former and 2.009(2) angstrom for the latter.