Superbulky metallocene complexes of the heavier alkaline-earth metals strontium and barium

Insight in cyclopentadienyl metal complexes with superbulky ligands: The crystal structure of [CpBIGK]∞

“…This disorder seems to increase with the polarizability of the metal and suggests that the more polarizable metals prefer to be slightly off-center. As pointed out earlier [7,8], induced metal polarization could enforce Cp-metal attraction (4). A similar induced-polarization-model (5) is in use to explain the typically observed bending of heavier alkaline-earth and lanthanide metallocenes [22].…”

“…1 is described. The C-HÁ Á ÁC(p) distances are somewhat longer than those found for the barocene ðCp BIG Þ 2 Ba (2.81 Å [8]) and, therefore, values slightly higher than the usual 2.90 Å cut-off value (i.e. the sum of the van der Waals radii for C and H) have been taken.…”

“…The ligand (4-nBu-C 6 H 4 ) 5 Cp, which we abbreviate as Cp BIG , gave access to various sandwich complexes (1-Ca, 1-Sr, 1-Ba, 1-Yb and 1-Sm) which are well-soluble in hexane at room temperature [7,8]. All complexes crystallize from this solvent isomorphously and their crystal structures show surprisingly ordered nBusubstituents.…”

“…These problems have been circumvented by slight modification of the ligand: substituents in the aryl ring greatly increase the solubility of the organometallic complexes [5][6][7][8]. Also, modification of the synthetic procedures gave access to single crystals of (Ph 5 Cp) 2 Ca, (Ph 5 Cp) 2 Ba and (Ph 5 Cp) 2 Yb [9].…”

“…the sum of the van der Waals radii for C and H; for the smaller metals these distances can be as short as 2.41 Å [7]), (ii) the aryl substituents typically bend out of the Cp-plane away from the metal, however, for large metals like Sm and Ba significant bending towards the metal is observed (3.5(1)°and 5.3(2)°, respectively). This outof-plane bending angle is linearly correlated to the size of the metal [8]. Although C-HÁ Á ÁC(p) hydrogen bonds are generally weak, the presence of 10 such interactions could contribute significantly to the stability of the metallocene.…”