Syntheses and X-ray Structures of Anionic Sodocene Sandwiches

Abstract

While, the lithocene anion (Cp2Li-) can simply be generated by reacting 2 equiv of CpLi with PPh4Cl in THF, the attempted synthesis of the sodocene anion under similar reaction conditions results in the crystallization of [Cp-][PPh4 +]. The structure consists of “naked” Cp anions pinched between metaphenyl hydrogens of the phosphonium cations. An ansa-sodocene anion in which the two Cp rings are bridged by a −C(Me)2−C(Me)2− chain is obtained by reaction of Me4C2(C5H4Na)2 with 1 equiv of PPh4Cl in THF. Its crystal structure shows a disordered ansa-sodocene anion containing a sandwiched sodium cation solvated by a THF molecule. Unbridged Cp2Na- was obtained by pushing the (CpNa + Cp-) ⇄ Cp2Na- equilibrium to the sodocene anion side. Cell dimensions, space group symmetry, and the molecular structure of [Cp2Na-][PPh4 +] are remarkably similar to that of [Cp2Li-][PPh4 +]. The anion can be described as a centrosymmetric (η5,η5)Cp2Na- sandwich (average C−Na = 2.630(3) Å) with approximate D 5 d symmetry.

[Cp3Ba]−: The First Structurally Characterized Barate Complex

“…This was also observed in the structures of the lithocene [1] and sodocene [4] anions (Figure 3). These interactions can be regarded as CH´´´Cp hydrogen bonds between the C dÀ ± H d dipole and the negatively charged p-electron system of the Cp ring.…”

“…[4] This is due to the much higher acidity of a tetrabutylphosphonium group compared to a tetraphenylphosphonium group.…”

Can C−H⋅⋅⋅C(π) Bonding Be Classified as Hydrogen Bonding? A Systematic Investigation of C−H⋅⋅⋅C(π) Bonding to Cyclopentadienyl Anions

“…Figure 11 shows that an off-centre C À H donor slightly directs itself to the edge of the Cp ring, which suggests that the CÀH´´C angles should also be considered. The angles for each CÀH´´´C and CÀH´´´Cp c contact, together with their average value hYi, are given in [24,14,25] Anionic alkali metallocenes can also function as donors in CÀH´´´Cp À hydrogen bonding. Detailed analyses of their crystal structures show that networks of intermolecular bonding do indeed exist (Figure 12).…”

Construction of double- and triple-decker sandwich compounds from half-sandwich compounds: a theoretical assessment

“…This conclusion is the same as that drawn from the dissociation energies. [28][29][30] c. M-side and M-middle mean the distances of M to the center of the above and the middle ring…”

“…Due to their special structures, properties, and extensive applications, a variety of binuclear and multinuclear metallocenes have been intensively studied experimentally and theoretically since the identification of the ferrocene (Cp 2 Fe) structure in 1952 [4,6,[23][24][25][26][27][28][29][30]. Frenking et al reported the geometries and metal-ligand bond dissociation energies of an inverted sandwich [E-Cp-E'] + complex (E, E'= group 13 element; Cp =cyclopentadienyl) [31].…”