Synthesis and Crystallographic Study of Indenyl and Isopropylated Indenyl Complexes of Calcium, Strontium, and Barium

1996-04-30T00:00:00Z (GMT) by Jason S. Overby Timothy P. Hanusa
Reaction of 2 equiv of potassium indenide (KInd) with AeI<sub>2</sub> (Ae = Ca, Sr, Ba) in THF produces the bis(indenyl) complexes (Ind)<sub>2</sub>Ae(thf)<i><sub>n</sub></i> (<i>n</i> = 1 for Sr, Ba; <i>n</i> = 2 for Ca) in high yields. The use of potassium 1,3-diisopropylindenide (KInd<sup>2i</sup>) with the same diiodides produces the analogous complexes (Ind<sup>2i</sup>)<sub>2</sub>Ae(thf)<i><sub>n</sub></i> (<i>n</i> = 1 for Ca; <i>n</i> = 2 for Sr and Ba). All the complexes are air-sensitive solids. Single-crystal X-ray diffraction studies were completed for (Ind)<sub>2</sub>Ca(thf)<sub>2</sub>, (Ind<sup>2i</sup>)<sub>2</sub>Ca(thf), (Ind<sup>2i</sup>)<sub>2</sub>Ba(thf)<sub>2</sub>, and (Ind)<sub>2</sub>Sr(thf); these represent the first structurally characterized indenyl complexes of the heavier alkaline-earth metals. The calcium and barium compounds are monomeric, with bent metallocene geometries and average Ae−C distances of 2.73(3), 2.69(2), and 3.03(4) Å for (Ind)<sub>2</sub>Ca(thf)<sub>2</sub>, (Ind<sup>2i</sup>)<sub>2</sub>Ca(thf), and (Ind<sup>2i</sup>)<sub>2</sub>Ba(thf)<sub>2</sub>, respectively. The strontium complex is an infinite coordination polymer, [(Ind)<sub>2</sub>Sr(thf)]<sub>∞</sub>, with both terminal (Sr−C = 2.94 Å (av)) and bridging (Sr−C = 3.07 Å (av)) indenyl ligands. Although the individual Sr−C bond distances differ as much as 0.25 Å, there is no clear indication of slippage toward an η<sup>3</sup>-configuration. The presence of the two isopropyl substituents on the indenyl ligands makes them effectively as bulky as triisopropylcyclopentadienyl rings.