Insight in Structures of Superbulky Metallocenes with the Cp^BIG Ligand: Theoretical Considerations of Decaphenyl Metallocenes

Abstract

The structures of a series of decaphenyl metallocenes (Ph 5 Cp) 2 M, which model superbulky metallocenes, are calculated by means of density functional theory including a semi-empirical correction for dispersion interactions (DFT+D). Through a detailed investigation of the calcocene it is shown that the interactions between the phenyl substituents of the two cyclopentadienyl ligands lead to a preference of S 10 symmetrical structures and that dispersion interactions contribute to the overall stability of superbulky metallocenes. Whereas

Physical Properties of Superbulky Lanthanide Metallocenes: Synthesis and Extraordinary Luminescence of [EuII(CpBIG)2] (CpBIG=(4‐nBu‐C6H4)5‐Cyclopentadienyl)

“…These non-classical C À H···C hydrogen bridges [12] are significantly shorter than the sum of the van der Waals radii for C and H. Although the energy involved in such interactions is quite low and close to the van der Waals limit of about 2-5 kcal mol À1 , [12,13] the presence of ten of these attractors could strongly contribute to the stability of such metallocenes. [7] For metallocenes with large metals, these attractions result in an unusual out-of-plane bending of ring substituents towards each other (Figure 1 b) and a linear correlation between metal size and out-of-plane bending could be deduced. [5] The highly favourable S 10 symmetric conformer has been calculated to be 5-6 kcal mol À1 lower in energy than the alternative D 5 symmetric isomer, in which the rings interact by means of a side-on p-stacking model (Figure 1 c).…”

“…The aryl rings of the Cp BIG ligand are engaged in CH⋅⋅⋅π interactions with the aromatic system of the aryl rings on the neighboring Cp BIG ligand (Figure 1 a). These non‐classical CH⋅⋅⋅C hydrogen bridges12 are significantly shorter than the sum of the van der Waals radii for C and H. Although the energy involved in such interactions is quite low and close to the van der Waals limit of about 2–5 kcal mol −1 ,12, 13 the presence of ten of these attractors could strongly contribute to the stability of such metallocenes 7. For metallocenes with large metals, these attractions result in an unusual out‐of‐plane bending of ring substituents towards each other (Figure 1 b) and a linear correlation between metal size and out‐of‐plane bending could be deduced 5.…”

“…[3] For this reason we recently reintroduced the superbulky metallocene ligand (4-nBuphenyl) 5 C 5 , [3b] which we have abbreviated throughout our work as Cp BIG . [4][5][6][7] Introduction of this ligand in lanthanide (Ln) chemistry led to surprising observations. Whereas half-sandwich complexes can be obtained simply by reaction of tris-A C H T U N G T R E N N U N G (benzyl)lanthanide precursors (Ln = Y, Dy, Nd, Tm) with Cp BIG H (Scheme 1), the attempted syntheses of such complexes for Yb and Sm instead led to spontaneous reduction of the lanthanide metal and the isolation of Ln II metallocenes.…”

“…[5] The highly favourable S 10 symmetric conformer has been calculated to be 5-6 kcal mol À1 lower in energy than the alternative D 5 symmetric isomer, in which the rings interact by means of a side-on p-stacking model (Figure 1 c). [7] This explains why decaarylmetallocenes crystallise exclusively as the S 10 symmetric conformer.…”

“…2 However, the development of the chemistry of the ligand in its simplest form (Ph 5 Cp) has been plagued by the complete insolubility of nearly all its complexes 3. For this reason we recently reintroduced the superbulky metallocene ligand (4‐ n Bu‐ phenyl) 5 C 5 ,3b which we have abbreviated throughout our work as Cp BIG 4–7…”