Conformational Control of Polysilanes: Use of CH2 Spacers in the Silicon Backbone
By the reaction of a number of oligosilyl potassium compounds with (trimethylsilyl)chloromethane, derivatives containing the (trimethylsilyl)methyl substituent were prepared. Using X-ray single-crystal structure analysis and UV spectroscopy the conformational properties of some of the compounds were studied. It was found that the (trimethylsilyl)methylated examples exhibit UV absorption properties which correspond to lower energy transitions in comparison to those of analogous trimethylsilylated molecules. The influence of this effect decreases, however, with increasing chain lengths.
Structure, Conformation, and UV Absorption Behavior of Partially Trimethylsilylated Oligosilane Chains
A number of new oligosilane chains containing linear segments with up to 18 silicon atoms were prepared. Employing salt elimination reactions of oligosilylpotassium compounds and oligosilylhalides, we prepared a number of tris(trimethylsilyl)silyl-terminated chains with varying internal segments consisting of dimethylsilylene and bis(trimethylsilyl)silylene units. Single-crystal X-ray diffraction and UV spectroscopic analysis indicate that the oligosilanes thus obtained are conformationally highly constrained due to steric interactions between trimethylsilyl groups. The chains consist of all-transoid-oriented segments, capable of σ-bond electron delocalization, which are separated by cisoid turns.
Polysilane derivatives of the transition metals II. The crystal and molecular structure of [tris(trimethylsilyl)silyl]pentacarbonylmanganese, (Me3Si)3SiMn(CO)5
Abstract The crystal and molecular structures of [tris(trimethylsilyl)silyl]pentacarbonylmanganese, (Me3Si)3SiMn(CO)5, have been determined from three-dimensional X-ray data obtained by counter methods. The compound crystallizes in space group P 1 of the triclinic system, with two molecules in a unit cell of dimensions: a = 9.002(2), b = 9.655(2), c = 15.639(3) A, α = 83.66(1), β = 105.65(1), γ = 114.61(1)°. The observed and calculated densities are 1.20 (±0.03) and 1.23 g-cm−3 respectively. Full-matrix least-squares refinement of the structure has led to a final value of the conventional R factor of 0.059 for the 818 independent reflections having F2 > 3σ(F2). The coordination geometry about the manganese atom is approximately octahedral and, about the silicon atom bonded to the manganese atom, tetrahedral. The relative orientations of carbonyl and trimethylsilyl groups, when viewed down the MnSi bond, appear consistent with minimization of energy due to nonbonded interactions. Two of the equatorial carbonyl groups are displaced out of the equatorial plane towards the silicon ligand by 6°. The SiMn bond is 2.564(6) A long and has no multiple character.