TY  - THES
AB  - Within this dissertation various compounds with interesting properties regarding chemical structure have been synthesised und characterised. The conversion of chloro and alkoxy substituted silanes in the presence of lithiated 1,3,5-trimethyl-1,3,5-triazacyclohexane to corresponding silane derivates could be achieved. Besides the usage of various alkoxy and alkyl substituents compounds with double substitution of the silicon atom with TMTAC units have been synthesised, which facilitates access to crystalline products. In sum thirteen silane derivatives could be isolated and spectroscopically characterised.
These include the compounds [MeN(CH2NMe)2CH]2Si(OMe)2 and [MeN(CH2NMe)2CH]2SiMe2, which were further analysed by X-ray diffraction of the crystalline state. The crystal structure of [MeN(CH2NMe)2CH]Si(OEt)3 and the parent heterocycle 1,3,5-trimethyl-1,3,5-triazacyclohexane could also be determined by means of X-ray diffraction of crystals obtained via low temperature zone melting. On the basis of the solid state structure of TMTAC it was feasible to confirm results from dipole measurements, NMR experiments in the liquid state and of quantum chemical calculations. These earlier contributions postulated that the exocyclic methyl groups in TMTAC adopt an aee conformation. In contrast [MeN(CH2NMe)2CH]2Si(OMe)2 prefers the seemingly energetic unfavourable aae conformation.
In spite of the large number of successfully synthesised mono- and di-substituted silanes, a threefold substitution at silicon could not be achieved. Quantum chemical calculations could illuminate the reasons for the failure to prepare of those silanes. For the compounds [MeN(CH2NMe)2CH]3SiMe and [MeN(CH2NMe)2CH]3SiH it is the overload with bulky substituents, which inhibits the formation of a such silanes substituted with three TMTAC units.
The reactivity of above compounds was explored with respect to metallation and hydrolysis. The reaction of [MeN(CH2NMe)2CH]2SiMe2 and [MeN(CH2NMe)2CH]SiMe2Ph with n-butyllithium resulted selectively in the deprotonation of the silicon bound methyl group. The lithiation product {[MeN(CH2NMe)2CH]2SiMe(CH2Li)}2 as was shown by determination of its crystal structure contains two monomers bridged by a [Li2C2]-square in the centre of the molecule. Hydrolysis of [MeN(CH2NMe)2CH]SiR3 (R = Me, Et, Ph) with hydrochloric acid resulted in the formation of the silanoles Et3SiOH, Ph3SiOH and Me2PhSiOH, rather than yielding the expected formylsilanes.
Furthermore the reactions of neutral TMTAC with the halosilanes SiF4, SiCl4 and SiBr4 have been investigated.
These resulted on the one hand a hydride abstraction of TMTAC and on the other hand [eta]3-coordinated siliconium complexes. In detail TMTAC and tetrafluorosilane react to give the cation [MeN(CH2NMe)2CH]+, which crystallises with the counterion [SiF5]-. In contrast, tetrachlorosilane as well as tetrabromosilane react with TMTAC preferably to afford the tridentate complexes [{(MeNCH2}3)SiCl3]+ Cl- and [{(MeNCH2}3)SiBr3]+ Br-. The silicon atom in these compounds shows a coordination number of six and is surrounded by its substituents in a distorted trigonal-antiprismatic manner.
The reaction of lithiated N,N-diethylhydroxylamine, lithiated N,N-dimethylaminoethanol and 2-[(dimethylamino-N-)benzyl-lithium with disilane derivates did not lead to the expected formation of substituted disilanes. Instead cleavage of the Si-Si bonds was observed resulting in the formation of Cl3SiONEt2, Cl3SiOCH2CH2NMe2 and products with the composition X3Si(C6H4)CH2NMe2 (X = OMe, Cl, F).
This leads to the conclusion that Si-Si bond in a disilane with electronegative substituents is unstable by presence of strong bases, which were employed in the above reactions. Besides the information of the decomposition of hexachlorodisilanes obtained by these reactions, experiments for the determination of the electron density of the unexpected but literature-known product Cl3SiCH2CH2NMe2 have been performed and could be analysed on the basis of the quantum theory of atoms in molecule (QTAIM). According to that a bond-critical point (BCP) between the atoms Si(1) und N(1) was found in the solid structure indicating a dative bond [Si···N: 2.065(1) Å]. The electron density at the BCP is 0.442(18) eÅ-3. This and other topology indicators describe the Si···N bond as closed shell-interaction, that means a predominantly ionic interaction.
In an excursion project the crystal structures of pentafluoropyridine (PFP) and 2,3,5,6-tetrafluoropyridine could be determined. The structural results could be compared to literature data obtained for high-pressure phases and the gasphase (microwave spectroscopy). Tetrafluoropyridine shows an interesting three-dimensional structure with TFP-chains.
DA  - 2010
KW  - Silicium , Silanderivate , Halogensilane , Alkoxysilane , Lithiierung , Cyclohexan , Trimethyltriazacyclohexane (TMTAC) , Donor , Akzeptor , Hyperkonjugation , Hyperkoordination ,
LA  - ger
PY  - 2010
TI  - Reaktivität von 1,3,5-Trimethyl-1,3,5-triazacyclohexan und dessen metallierter Form gegenüber Halogen- und Alkoxysilanen
UR  - https://nbn-resolving.org/urn:nbn:de:hbz:361-17671
Y2  - 2024-11-25T04:04:29
ER  -