Synthesis and characterization of new oligosilane derivatives of iron and molybdenum

By use of salt elimination, the transition metal substituted oligosilanes (η⁵-C₅Me₄Et)Fe(CO)₂SiMe₂SiMe₂Cl 1, (η⁵-C₅Me₄Et)Mo(CO)₃SiMe₂SiMe₂Br 2, (η⁵-C₅Me₄Et)Fe(CO)₂(SiMe₂)₆(CO)₂Fe(η⁵-C₅Me₄Et) 3 and (η⁵-C₅Me₄Et)Fe(CO)₂(SiMe₂)₆Br 4 were prepared and characterized. Compound 1 is well crystallized from pentane and its structure has been determined by X-ray diffraction analysis.     

Oligosilyl-Quecksilber und -Alkalimetallverbindungen

Oligo-silyl-mercury compounds (Si _{nR 2n+1})₂Hg (R=aryl, halogens) are synthesized from the siliconmonohydrides by reaction with (t-Bu)₂Hg and characterized. Treatment of the Silyl-mercury compounds with Na/K- alloy yields the corresponding alkali metal derivatives. Both reactions are very well suitable for the synthesis of oligosilanes.

Herrn Prof. Dr.K. Komarek zum 60. Geburtstag gewidmet.     

An Electrochemical Strategy to Synthesize Disilanes and Oligosilanes from Chlorosilanes**

Silanes are important compounds in industrial and synthetic chemistry. Here, we develop a general approach for the synthesis of disilanes as well as linear and cyclic oligosilanes via the reductive activation of readily available chlorosilanes. The efficient and selective generation of silyl anion intermediates, which are arduous to achieve by other means, allows for the synthesis of various novel oligosilanes by heterocoupling. In particular, this work presents a modular synthesis for a variety of functionalized cyclosilanes, which may give rise to materials with distinct properties from linear silanes but remain challenging synthetic targets. In comparison to the traditional Wurtz coupling, our method features milder conditions and improved chemoselectivity, broadening the functional groups that are compatible in oligosilane preparation. Computational studies support a mechanism whereby differential activation of sterically and electronically distinct chlorosilanes are achieved in an electrochemically driven radical-polar crossover mechanism.     

Über α,ω-übergangsmetallsubstituierte Oligosilane

Summary Methyloligosilanes withn=3, 4, 5 and 6 with dicarbonyl-cyclopentadienyl-iron- and tricarbonyl-triphenylphosphane-cobalt-groups in terminal positions were synthesized for the first time and characterized by NMR, IR, and MS. The NMR spectra were discussed in detail.

Herrn Prof. Dr. h.c. Ulrich Wannagat zum 70. Geburtstag gewidmet.     

Synthesis of di- and trisilanes with potentially chelating substituents

Silylenes 2 or 4, generated by thermolysis of cyclotrisilanes 1 and 3, were inserted into the SiCl or SiH bonds of monosilanes to yield a variety of disilanes, which can be further functionalized subsequently. In a few cases, trisilanes are accessible by the reaction of 1 with disilanes. The reaction of a metalated silane with a chlorosilane is an alternative method for the formation of SiSi bonds, which turned out to be especially useful for the synthesis of bulkily substituted disilanes. Some of the new dichlorodi- and trisilanes themselves serve as thermal precursors of silylenes 2 or 4, the extrusion of which can be catalyzed by 1 or 3 in certain cases.     

Oligosilane‐ and Oligosiloxane‐bridged Phosphines – Synthesis,Structures, and Metalation

The range of molecular silicon phosphorus compounds has been extended by some new species containing oligosilane ((R₂Si)_n; n ≥ 2) or oligosiloxane ((R₂SiO)_mSiR₂; m ≥ 1) fragments bound to phosphorus atoms. Primary and secondary compounds of these types allow for the synthesis of metal derivatives. Such metalated species usually form oligomers and exhibit a versatile structural chemistry with cyclic, polycyclic, and cage‐like patterns. The main results obtained in the field of oligosilane‐ and oligosiloxane‐bridged phosphines will be presented below and the structures of the metal derivatives will be discussed. Moreover, the synthesis of an inorganic ligand on the basis of siloxane‐bridged phosphines will be presented. This compound opens up a new chapter in host‐guest chemistry.     

Siliciumverbindungen mit starken intramolekularen sterischen Wechselwirkungen,XXIX Octacyclohexylcyclotetrasilan

Reductive halogen elimination from 1,4-dichlorooctacyclohexyltetrasilane gives octacyclohexylcyclotetrasilane (4) in high yield. The X-ray structure analysis of4 reveals a folded Si₄-framework with an angle of 27.6° between the two halves of the puckered ring corresponding to a Si-Si bond lengthening tod=239.1 pm. All cyclohexyl rings assume a chair conformation.