BIS(TERT-BUTYLCYCLOPENTADIENYL)MAGNESIUM, BIS(TERT-BUTYLCYCLOPENTADIENYL)CALCIUM, BIS(TERT-BUTYLCYCLOPENTADIENYL)STRONTIUM, AND BIS(TERT-BUTYLCYCLOPENTADIENYL)BARIUM METALLOCENES

Bis(tert-butylcyclopentadienyl)metal derivatives, M(t-BuC5H4)2, M= Mg, Ca, Sr, and Ba, have been prepared by metalation using Mg(s-Bu)(n-Bu) or metal vapors for the heavier group 2 elements. The Ca, Sr, and Ba compounds are only sparingly soluble in hydrocarbon solvents and have been characterized by using C-13 CP/MAS NMR spectroscopy with TOSS pulse sequences. Addition of THF (tetrahydrofuran) to these compounds yields THF adducts that have been isolated as [M(t-BuC5H4)2(THF)2] for Ca and Sr. Both have been structurally characterized, along with [Mg(t-BuC5H4)2]. The latter is a regular metallocene: Mg-centroid = 2.00 angstrom, centroid-Mg-centroid = 180-degrees; crystals are monoclinic, space group P2(1)/n, a = 6.270 (4) angstrom, b = 11.213 (3) angstrom, c = 11.932 (7) angstrom, beta = 96.53-degrees, V = 833.6 angstrom 3, Z = 2. The THF adducts are isostructural and are monomeric bent metallocenes, with four coordinate metal centers, assuming the cyclopentadienyl ligands to be unidentate: Ca,Sr-centroid = 2.46, 2.61 angstrom, Ca,Sr-O = 2.40, 2.53 angstrom, centroid-M-centroid = 133.3, 133.1-degrees, O-M-O = 83.2 (2), 83.1 (2)-degrees; crystals are monoclinic, space group P2(1)/n, a = 13.527 (4), 13.793 (3) angstrom, b = 10.057 (4), 10.308 (1) angstrom, c = 20.254 (7), 20.269 (5) angstrom, beta = 106.24 (1), 107.66 (1)-degrees, V = 2445 (1), 2746 (1) angstrom 3, Z = 4 (Ca, Sr values, respectively).