FU Berlin Digitale Dissertation
Sven Kleinhenz : Homoleptic Methylcompounds from Elements of the 4th and 5th Subgroup Homoleptische Methylverbindungen von Elementen der 4. und 5. Nebengruppe
|Abstract| |Table of Contents| |More Information|

Abstract By reacting the transition metals Ti, Nb and Ta with dimethylzinc and methyllithium it was possible to synthesise and structurally characterise the following substances: TiCl3(CH3)·O(C2H5)2, TiCl2(CH3)2, TiCl(CH3)3, TiCl(CH3)3·O(C2H5)2, Li[Ti(CH3)5, Ti(CH3)4·O(C2H5)2,], Li[Ti(CH3)5·Ti(CH3)4], Ta(CH3)5, Li[Nb(CH3)6], Li[Ta(CH3)6] Because tetramethyltitanium is an electronless strong lewisacid, it was not possible to obtain it without diethylether coordination. The crystal structure of tetramethyltitanium-diethylether is a trigonal pyramide, with ether in the axial position. In a ,mixed? compound from tetramethyltitanium and pentamethyltitanate, [Ti(CH3)4-Ti(CH3)5]1-, the two molecules are bonded over a ,agostic? interaction of a methylgroup. Results of ab initio calculations show that this molecule would be 58 kJ mol-1 more stable than the free tetramethyltitanium and pentamethyltitanat. The ether complex of Ti(CH3)4 would be 11,8 kJ mol-1 more stable than the free tetramethyltitanium. The pentamethyltitanate´s crystal structure is a strong distorted tetragonal pyramid. An ab initio calculation showed that the tetragonal pyramidal geometry has a lower energy, 10,5 kJ mol-1, than the trigonal pyramidal. The structures of partly methylated titaniumcompounds have all a distorted octahedral coordination. In the crystal the molecules are associated via chlorine bridges (trichlormethyltitanium, chlortrimethyltitanium and dichlordimethyltitanium). Also a solvent molecule can be bonded to the titanium to get a sixfolded coordination. In the fifthfold coordinated compounds, Ti(CH3)4·O(C2H5)2, TiCl(CH3)3·O(C2H5)2 the most electronegative ligands occupy the apical positions. Pentamethyltantalum has a tetragonal pyramidal geometry, just like the ab initio calculations predicted it. The hexamethyllates from tantalum and niobium have a trigonal prismatic structure, they are only very light distorted compared with Hexamethyltungsten.

Table of Contents Download the whole PhDthesis as a zip-tar file or as zip-File For download in PDF format click the chapter title Titelblatt und Inhaltsverzeichnis 1 Einleitung 2 Allgemeiner Teil 2.1 Einführung 2.2 Darstellung und Eigenschaften von Pentamethyltantal 2.3 Darstellung und Eigenschaften von Lithiumhexamethyltantalat und -niobat 2.4 Darstellung und Eigenschaften von Hexaphenyl- und Hexatoloyltantalat 2.5 Darstellung und Eigenschaften von Titanmethylverbindungen 3 Praktischer Teil 3.1 Verwendete Geräte - Allgemeine Einfhrung 3.2 Vorhandene Substanzen 3.3 Synthesen 4 Zusammenfassung - Summary 5 Anhang 5.1 Abkürzungen 5.2 Aus dieser Arbeit bereits erfolgte Publikationen 6 Literatur

More Information:
Online available:	http://www.diss.fu-berlin.de/1998/24/indexe.html
Language of PhDThesis:	german
Keywords:	Niobium; Tantalum; Titanium; Methylcompounds ;structure calculation
DNB-Sachgruppe:	30 Chemie
Date of disputation:	23-Nov-98
PhDThesis from:	Department Chemie, Freie Universität Berlin
First Referee:	Prof. Dr. Konrad Seppelt
Second Referee:	Prof. Dr. F. Ekkehardt Hahn ( Münster)
Contact (Author):	kleinhen@chemie.fu-berlin.de
Contact (Advisor):	seppelt@chemie.fu-berlin.de
Date created:	10-Dec-98
Date available:	07-Jul-99

 

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