Calcium, strontium, barium, and ytterbium complexes with cyclooctatetraenyl or cyclononatetraenyl ligands

Neutral triple-decker complexes of the heavy alkaline earth metals and ytterbium with tetraisopropylcyclopentadienide anions as terminal ligands and a cyclooctatetraene dianion as a middle deck have been synthesized from tetraisopropylcyclopentadienyl metal halide precursors and disodium cyclooctatetraenide. The pentaisopropylcyclopentadienyl analogue [{(C-5(1) Pr-5)Yb}(2)(C8H8)] was prepared from ytterbium metal, cyclooctatetraene, and the free pentaisopropylcyclopentadienyl radical. X-ray crystal structure determinations for the barium and the calcium derivative show an almost linear arrangement of ring centers and metal atoms in both cases with metal-ring center distances of 2.33 angstrom (Ca-Cp), 1.99/1.98 angstrom (Ca-COT) and 2.71 angstrom (Ba-Cp), 2.40 angstrom (Ba-COT). The geometrical features of these molecules could be modeled quite accurately with density functional calculations. With potassium cyclononatetraenide, sparingly soluble bis(cyclononatetraenyl) barium could be prepared and characterized by H-1 and C-13 NMR spectroscopy, mass spectrometry, and elemental analysis. Cyclononatetraenyl(tetraisopropylcyclopentadienyl)barium was obtained from [(C(5)HiPr(4))Bal(THF)(2)](2) and KC9H9 as a 1:1 mixture with octaisopropylbarocene. Density functional calculations predict sandwich structures with parallel rings and a 2.37 P, Ba-ring distance for [Ba(C9H9)(2)] and a 174 degrees bending with metal-ring distances of 2.72 angstrom (Ba-Cp) and 2.35 angstrom (Ba-CNT) for [(C(5)HiPr(4))Ba(C9H9)]. All alkaline earth sandwich and triple-decker complexes mentioned above have been heated to 250 degrees C without decomposition and have been sublimed in oil pump vacuum.