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

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journal contribution
posted on 30.04.1996, 00:00 by Jason S. Overby, Timothy P. Hanusa
Reaction of 2 equiv of potassium indenide (KInd) with AeI2 (Ae = Ca, Sr, Ba) in THF produces the bis(indenyl) complexes (Ind)2Ae(thf)n (n = 1 for Sr, Ba; n = 2 for Ca) in high yields. The use of potassium 1,3-diisopropylindenide (KInd2i) with the same diiodides produces the analogous complexes (Ind2i)2Ae(thf)n (n = 1 for Ca; n = 2 for Sr and Ba). All the complexes are air-sensitive solids. Single-crystal X-ray diffraction studies were completed for (Ind)2Ca(thf)2, (Ind2i)2Ca(thf), (Ind2i)2Ba(thf)2, and (Ind)2Sr(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)2Ca(thf)2, (Ind2i)2Ca(thf), and (Ind2i)2Ba(thf)2, respectively. The strontium complex is an infinite coordination polymer, [(Ind)2Sr(thf)], 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 η3-configuration. The presence of the two isopropyl substituents on the indenyl ligands makes them effectively as bulky as triisopropylcyclopentadienyl rings.