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| - Calcium, Strontium, Barium, and Ytterbium Complexes withCyclooctatetraenyl or Cyclononatetraenyl Ligands1
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| - 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 havebeen synthesized from tetraisopropylcyclopentadienyl metal halide precursors and disodium cyclooctatetraenide. The pentaisopropylcyclopentadienyl analogue [{(C5iPr5)Yb}2(C8H8)] was prepared from ytterbiummetal, cyclooctatetraene, and the free pentaisopropylcyclopentadienyl radical. X-ray crystal structuredeterminations for the barium and the calcium derivative show an almost linear arrangement of ring centersand metal atoms in both cases with metal−ring center distances of 2.33 Å (Ca−Cp), 1.99/1.98 Å (Ca−COT) and 2.71 Å (Ba−Cp), 2.40 Å (Ba−COT). The geometrical features of these molecules could bemodeled quite accurately with density functional calculations. With potassium cyclononatetraenide, sparinglysoluble bis(cyclononatetraenyl)barium could be prepared and characterized by 1H and 13C NMR spectroscopy, mass spectrometry, and elemental analysis. Cyclononatetraenyl(tetraisopropylcyclopentadienyl)barium was obtained from [(C5HiPr4)BaI(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 Å Ba−ring distancefor [Ba(C9H9)2] and a 174° bending with metal−ring distances of 2.72 Å (Ba−Cp) and 2.35 Å (Ba−CNT)for [(C5HiPr4)Ba(C9H9)]. All alkaline earth sandwich and triple-decker complexes mentioned above havebeen heated to 250 °C without decomposition and have been sublimed in oil pump vacuum.
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