SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF HEXA(CYCLOHEXYL)FERROCENE, [1,2,4-(C6H11)3C5H2]2FE

1,2,4-tricyclohexylcyclopentadiene can be formed from the phase-transfer catalyzed addition of cyclohexyl bromide to cyclopentadiene. Reaction of two equivalents of its lithium salt with FeCl2 in THF produces the corresponding substituted ferrocene. Crystals of orange [1,2,4-(C6H11)3C5H2]2Fe grown from toluene are monoclinic, space group C2/c, with a = 16.386 (4) Angstrom, b = 12.142 (3) Angstrom, c = 21.003 (3) Angstrom, beta = 107.38 (1), and D(calcd) = 1.131 g cm-3 for Z = 4. Least-squares refinement based on 1291 observed reflections led to a final R value of 0.049. The molecule possesses a classic sandwich geometry with staggered rings and a crystallographically imposed two-fold rotation axis passing through the metal center. Despite the presence of six cyclohexyl rings, the cyclopentadienyl ligands can orient themselves around the iron to avoid unfavorable inter-ring steric interactions. As a result, the average Fe-C ring distance of 2.06 (1) angstrom in hexa(cyclohexyl)ferrocene is not significantly longer than the corresponding distance in ferrocene itself.