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Encapsulated alkaline earth metallocenes. 3: Structural influences on phase transformations alkaline earth complexes

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Abstract

Reaction of two equivalents of KCp3i (Cp3i ≡ 1,2,4-(i-Pr)3C5H2) with MgBr2 in Et2O produces the base-free metallocene (Cp3i)2Mg in high yield; the similarly prepared organocalcium complex (Cp3i)2Ca, although initally isolated as an oil, forms a crystalline solid on standing for several months. Crystals of (Cp3i)2 CA are tetragonal, space group P42/n, with a = 18.147(4), c = 15.996(4) Å, Å and Dcalc = 1.066 g cm−3 for Z = 8. Lease-squares refinement based on 2044 reflections led to a final R-value of 0.072. The complex possesses a metallocene geometry that is slightly bent; the average Ca–C distance is 2.62(2) Å and the right centroid–Ca–ring centroid angle is 169.7°. Comparison of these complexes with previously reported alkaline earth metallocenes suggests that the volatility of the metallocenses depends primarily on the degree of aggregation in the solid state, whereas the melting point of the nonomeric compounds varies with the asymmetry and ligan flexibility in the complex.

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