A homologous series of base-free organo(alkaline-earth) metallocenes: Synthesis and molecular structures of [1,2,4-(SiMe3) 3C5H2]2(Ca, Sr, Ba)

Melanie J. Harvey, Keith T. Quisenberry, Timothy P. Hanusa, Victor G. Young

Research output: Contribution to journalArticlepeer-review

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Abstract

Bis[1,2,4-tris(trimethylsilyl)cyclopentadienyl] complexes [1,2,4-(SiMe 3)3C5H2]2Ae [(Cp 3Si)2Ae; Ae = Ca (1), Sr (2), Ba (3)] are isolated from the 2:1 reaction of K[Cp3Si] and AeI2 in diethyl ether. Under the same reaction conditions used for the heavier metallocenes the corresponding (Cp3Si)2Be compound was not formed, although calculations suggest that the beryllocene would be sterically feasible. Compound 1 crystallizes as a bent monomer from hexanes (ring centroid-Ca-ring centroid = 166.7°) with two η5-Cp3Si ligands on the calcium atom [Ca-C(av) = 2.63(2) Å]. Metallocene 2, the first crystallographically characterized example of an unsolvated strontocene, is also isolated as a bent monomer (159.4°) from hexanes with two η 5-Cp3Si ligands on the strontium atom [Sr-C(av) = 2.819(2) Å]. Compound 3 crystallizes on sublimation as a coordination dimer in which each barium atom is flanked by two η5-Cp3Si rings [Ba-C(av) = 3.01(2) Å] and one methyl group from a neighboring Cp′ ring; the intermolecular Ba⋯C(methyl)′ distance is 3.275(6) Å. The amount of bending observed in 1-3 and other Group-2 metallocenes varies with the metals, the steric bulk of the cyclopentadienyl ligands, and crystal packing effects, and is not easily predictable. (

Original languageEnglish (US)
Pages (from-to)3383-3390
Number of pages8
JournalEuropean Journal of Inorganic Chemistry
Issue number18
DOIs
StatePublished - Sep 26 2003

Keywords

  • Alkaline-earth metals
  • Metallocenes
  • Solid-state structures

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