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

Abstract

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.

Capillary isotachophoresis for the analysis of ionic liquid entities

“…Cyclopentadienyl complexes of Ca, Sr, and Ba always crystallize as contact ion pairs in which the two carbanions are directly bound to the metal atom 10. Indenyl11 and fluorenyl12 complexes also form contact ion pairs. What are the driving forces for the formation of the SSIP [Ca 2+ (thf) 6 ][Me 3 Si(fluorenyl − )] 2 ?…”

“Alkaline-Earth Metals in a Box”: Structures of Solvent-Separated Ion Pairs

“…Cyclopentadienyl complexes of Ca, Sr, and Ba always crystallize as contact ion pairs in which the two carbanions are directly bound to the metal atom. [10] Indenyl [11] and fluorenyl [12] complexes also form contact ion pairs. What are the driving forces for the formation of the SSIP [Ca 2 (thf) 6 ][Me 3 Si(fluorenyl À )] 2 ?…”

Bis(allyl)calcium

“…In contrast to the widely employed organomagnesium and organolithium compounds,1, 2 the σ and π complexes of the heavier alkaline earth metals calcium, strontium, and barium3 have not achieved their full potential. Whereas the chemistry of cyclopentadienyl (Cp) calcium compounds is fairly well developed, that of Cp‐free alkyl,4 alkynyl,5 aryl,6 benzyl,7 indenyl,8 and fluorenyl9 calcium compounds has just begun unfolding. Allyl calcium compounds of unknown structure were first mentioned in a patent as polymerization initiators for vinylic monomers 10.…”