ENCAPSULATED ALKALINE-EARTH METALLOCENES .2. TRIISOPROPYLCYCLOPENTADIENYL SYSTEMS, [(C3H7)3C5H2]2AE(THF)N (AE = CA, SR, BA - N = 0-2), AND THE CRYSTAL-STRUCTURE OF [(C3H7)3C5H2]2BA(THF)2

Reaction of 2 equiv of KCp3i (Cp3i = 1,2,4-(C3H7)3C5H2) with AeI2 (Ae = Ca, Sr, Ba) in Et2O, THF, or THF/toluene produces the metallocenes (Cp3i)2Ae(THF)n (n = 0-2) in high yields. Both the monosolvated and base-free (Cp3i)2Ca(THF)n species are isolated as oily materials that partially solidify on long standing, whereas the mono- and disolvated strontium and barium complexes are solids. The base-free strontocene is an oil, and the corresponding barocene is initially isolated as a wax that solidifies on standing for several weeks. These unusual physical properties are apparently related to the inability of certain metal/ligand combinations to pack efficiently in ionic lattices. All the metallocenes sublime or distill at or below 140-degrees-C at 10(-6) Torr. Crystals of (Cp3i)2Ba(THF)2 grown from THF/hexane are monoclinic, space group C2/c, with a = 13.95(1) angstrom, b = 14.577(8) angstrom, c = 18.661(9) angstrom, beta = 104.28(4)-degrees, and D(c) = 1.200 g cm-3 for Z = 4. Least-squares refinement based on 1669 observed reflections led to a final R value of 0.068. The complex possesses a bent metallocene geometry and contains a crystallographically imposed 2-fold rotation axis passing through the barium. The average Ba-C and Ba-O(THF) distances are 3.03(2) and 2.77(1) angstrom, respectively, and the ring centroid-Ca-ring centroid angle is 132-degrees. The i-Pr groups on the side of the metallocene away from the THF have rotated and lie nearly in line with the Cp rings. This allows the Cp3i rings to bend back to accommodate the THF ligands without undue steric crowding.