A Theoretical Study of the Half-Sandwich Silicon(II) Cation [(Me5C5)Si]+ and of the Cationic Complex [(Me5C5)Si (DME)]+

Abstract

Ab-initio calculations have been performed for the half-sandwich cation [(Me 5 C 5 )Si] + and its DME complex [(Me 5 C 5 )Si(DME)] + . For these cations, the ground state energies, the complexation energy, the frontier orbitals, the vertical singlet-triplet excitation energies, and the natural atomic charges have been calculated. In both cations, the "lone-pair" at silicon does not represent the HOMO. The nature of the weak dative O → Si bond can best be described in terms of electrostatic and attractive dispersion interactions. The DME coordination destabilizes the cluster orbitals and slightly enhances the positive charge at silicon.

The Pentamethylcyclopentadienylsilicon(II) Cation as a Catalyst for the Specific Degradation of Oligo(ethyleneglycol) Diethers

“…The long SiF distances (>3.34 Å) are in accord with an ionic structure. The structural parameters of the [Cp*Si(dme)] + cation calculated at the ab initio MP2/TZVPP level are nearly identical to those found experimentally for the cation in compound 7 ; the weak SiO bonding is based on purely electrostatic and van der Waals type interactions 19…”

The Pentamethylcyclopentadienylsilicon(II) Cation: Synthesis, Characterization, and Reactivity

“…According to theoretical calculations, the electron density of the FeSi bond in 13 is mainly located at iron (74.2 %) and less at silicon (25.8 %). Following the population analysis, a charge of + 0.216 is remaining at the Cp*Si fragment (for comparison: +0.99 in [Cp*Si] + 55).…”

“…The two SiO interactions cause a reduction of the covalent character of the Cp*Si bond. As a result, the positive charge at silicon (+1.11 in 17 , +0.96 in 1 ) and the negative charge at the Cp* fragment (−0.21 in 17 , +0.04 in 1 ) is slightly increased 55…”

The Pentamethylcyclopentadienylsilicon(II) Cation as a Catalyst for the Specific Degradation of Oligo(ethyleneglycol) Diethers

“…Despite the instability of complex 7, we could ascertain its structure by X-ray analysis ( Figure 1). [18] The DME molecule coordinates rather weakly in an asymmetric bidentate fashion to the silicon atom, and the Cp* ligand shows some deviation from h 5 bonding towards h 3 bonding. The average SiÀC [19] Interestingly, the complex [Cp*Si(dme)] + B(C 6 F 5 ) 4 À (7) decomposed in CD 2 Cl 2 solution within several days, whereby the DME molecule was transformed into dimethyl ether and 1,4-dioxane [see Eq.…”

“…Crystals of the air-sensitive ionic complex [Cp*Si( [12]crown-4)] + B(C 6 F 5 ) 4 À (8) were obtained from a solution of 6 and [12]crown-4 in a CH 2 Cl 2 /hexane mixture. An X-ray analysis of 8 [18] shows that four oxygen atoms of the crown ether molecule are weakly coordinated to the silicon atom of the Cp*Si unit; the latter shows only small deviations from h 5 bonding, but longer Si À C distances (average value 2.191 ) compared with the situation in the etherfree Cp*Si + cation (2.147 ; see Figure 1). Such a halfsandwich-like crown ether coordination to a silicon atom is thus presented herein for the first time.…”