FORMATION AND REACTIONS OF MONO(PERALKYLCYCLOPENTADIENYL) AND BIS(PERALKYLCYCLOPENTADIENYL) COMPLEXES OF CALCIUM AND BARIUM - THE X-RAY CRYSTAL-STRUCTURE OF [(ME4ETC5)CA(MU-NSIME2CH2CH2SIME2)]2

The reaction of K(Me4EtC5) and CaI2 in THF forms the colorless metallocene (Me4EtC5)2Ca(THF) in high yield. Both it and Cp*2Ca(THF)2 (Cp* = Me5C5) can be used in a variety of reactions to form mono(peralkylcyclopentadienyl) complexes of calcium, in which disproportionation via Schlenk equilibrium plays a smaller than expected role. Thus, (Me4EtC5)CaI(THF)2 reacts with K[OC6H2-t-Bu2-2,6-Me-4], K[Otamp] (Otamp = 2,4,6-tris[(dimethylamino)methyl]phenoxide) or KNSiMe2CH2CH2SiMe2 to produce (Me4EtC5)Ca(OC6H2-t-Bu2-2,6-Me-4), (Me4EtC5)Ca(Otamp), and [(Me4EtC5)Ca(mu-NSiMe2CH2CH2SiMe2)]2. These compounds represent the first mixed cyclopentadienyl amide or aryl oxide complexes of the heavy alkaline-earth metals to be described. Crystals of [(Me4EtC5)Ca(mu-NSiMe2CH2CH2SiMe2)]2 grown from toluene are monoclinic, space group P2(1)/a, with a = 17.846 (4) angstrom, b = 12.405 (2) angstrom, c = 18.140 (3) angstrom, beta = 97.32 (1)-degrees and D(calcd) = 1.160 g cm-3 for Z = 4. Least-squares refinement on the basis of 2200 observed reflections measured at -172-degrees-C led to a final R value of 0.057. The compound crystallizes in the form of a dimer containing a planar [Ca-N-]2 ring. The two shorter Ca-N distances average 2.41 (1) angstrom, and the two longer Ca-N' distances average 2.48 (1) angstrom. The average Ca-C(ring) distance is 2.70 (3) angstrom. Cp*2Ca(THF)2 (Cp* = Me5C5) reacts with LiN(SiMe3)2 and LiCH(SiMe3)2 in THF to form a precipitate of LiCp* and generate the hydrocarbon-soluble mono(pentamethylcyclopentadienyl) complexes Cp*CaE(THF)3 (E = N(SiMe3)2, CH(SiMe3)2). Mixing THF solutions of Cp*2Ba(THF)2 with LiN(SiMe3)2 or LiCH(SiMe3)2 does not form LiCp*, and the hydrocarbon-insoluble organoborates Li[Cp*2BaE](THF)2 (E = N(SiMe3)2, CH(SiMe3)2) can be isolated from the reaction mixtures in near quantitative yield.