Synthesis of a monopentamethylcyclopentadienyl halide complex of calcium. The x-ray crystal structure of [(Me5C5)Ca(.mu.-I)(THF)2]2

Heterofunctionalization catalysis with organometallic complexes of calcium, strontium and barium

“…Work by Hanusa has shown that a number of heteroleptic heavier alkaline earth complexes including halides (McCormick et al 1989;Burkey et al 1994;, acetylides (Burkey & Hanusa 1996), amides (Sockwell et al 1992) and a calcium borohydride ; figure 3; X 1 = I, C ≡ CR, NR 2 , HBR 3 ) may be kinetically stabilized by the application of bulky cyclopentadienyl ligands allowing their synthesis and characterization in the solid state. Many of these compounds, however, have proven unstable in solution and readily undergo Schlenk-like equilibria, and it is notable that little or no further reaction chemistry has been forthcoming from this approach.…”

Alkali and Alkaline Earth Metal Complexes Ligated by an Ethynyl Substituted Cyclopentadienyl Ligand

“…The two bridging iodide anions show a short and a slightly elongated Ca-I bond (Ca1-I1 3.0920(7) Å and Ca1-I1 3.2039(7) Å). The average cyclopentadienyl carbon calcium distances in 3 (2.6948 Å) are comparable to those in [Cp*CaI(THF) 2 ] 2 (2.67 Å) [28]. As a result of the steric demand, the two ethynyl substituents point to opposite directions.…”

Stability of cyclopentadienyl aryloxide complexes of calcium and barium

“…Also unusual is the upfield shift observed for the [Cp*] − resonance in C 6 D 6 (1.79 ppm), when compared to the analogous peak for the metallocene Cp* 2 Ba (1.97 ppm). This contrasts with that of the corresponding mono(ring) complexes of calcium Cp*CaX(thf) n , which have [Cp*] − resonances shifted downfield from the same peak for Cp* 2 Ca [7,8]. C 6 D 6 and THF-d 8 solutions of isolated Cp*Ba(BHT)(thf) allowed to stand for up to 72 h under ambient conditions do not exhibit any noticeable changes in their 1 H NMR spectra.…”

“…Nevertheless, the highly electropositive character of these metals and the lack of valence electrons in their cations are associated with high kinetic lability in many Cp MX compounds [6]. Archetypal examples include Cp CaI(thf) n (Cp = C 5 Me 5 or C 5 Me 4 Et) complexes, which undergo Schlenk-type rearrangement in THF solution to form 2:1:1 mixtures of Cp CaI(thf) n , Cp 2 Ca, and CaI 2 , respectively [7,8]. The position of equilibrium can be shifted somewhat by the solvent (aromatic solvents favor the heteroleptic species) and by the use of "encapsulating" cyclopentadienyl rings such C 5 (i-Pr) 4 H (=Cp 4i ) [1,3], C 5 (SiMe 3 ) 3 H 2 (=Cp 3Si ) [2] and C 5 (t-Bu) 3 H 2 [9], which sterically interfere with the rearrangement process.…”