om950810x_si_001.pdf (781.84 kB)

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

Download (781.84 kB)
journal contribution
posted on 30.04.1996 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.