Asymmetric synthesis of chiral at metal complexes with pentadentate bis(oxazoline) ligands [Elektronische Ressource] / vorgelegt von Michael Seitz

Informations

• Publié par: universitat_regensburg
• Publié le: 01 janvier 2005
• Nombre de lectures: 15
• Langue: Deutsch
• Poids de l'ouvrage: 6 Mo

Extrait

Asymmetric Synthesis of Chiral-at-
Metal Complexes with Pentadentate
Bis(oxazoline) Ligands



Dissertation zur Erlangung
des Doktorgrades der Naturwissenschaften (Dr. rer. nat.)
der Naturwissenschaftlichen Fakultät IV – Chemie und Pharmazie






vorgelegt von
Michael Seitz
aus Passau

2004




















Diese Arbeit wurde angeleitet von Prof. Dr. O. Reiser

Promotionsgesuch eingereicht am: 24.06.2004

Tag der mündlichen Prüfung: 15.07.2004

Prüfungsausschuß: Prof. Dr. G. Schmeer (Vorsitzender)
Prof. Dr. O. Reiser (1. Gutachter)
Prof. Dr. H. Brunner (2. Gutachter)
Prof. Dr. G. Märkl (3. Prüfer)
IIDie vorliegende Arbeit entstand in der Zeit von November 2000 bis Juli 2004 am
Lehrstuhl Prof. Dr. O. Reiser, Institut für Organische Chemie, Universität Regensburg
und im Rahmen eines Auslandsaufenthaltes von Februar bis Mai 2003 in der
Arbeitsgruppe von Prof. Dr. A. S. Borovik am Department of Chemistry, University of
Kansas (Lawrence, USA).






















Ich danke meinem Lehrer,

Herrn Prof. Dr. O. Reiser

für die interessant Themenstellung, die beständige Unterstützung in jeglicher
Hinsicht und das entgegengebrachte Vertrauen.

III

































IV














für Jana


















V Table of Contents


0 Preface 1

1 Introduction 4
1.1 Background 4
1.2 Aim of this Work 9

2. Ligand Synthesis 17
2.1 Synthesis of the Pyridine Units 18
2.2 Synt the Oxazoline Units 19
2.3 Assembly of the Ligands 22

3 Complex Synthesis 25
3.1 Perchlorate Complexes of First-Row Transition Metals 25
3.2 Triflate Complexes of First-Row Transition Metals 27
3.3 Miscellaneous Complexes 28

4 Structural Investigations 32
4.1 General Considerations 32
4.2 Solid State Structures 34
4.3 NMR-Spectroscopy 42
4.4 CD-Spect 47

5 Multinuclear Assemblies 57
5.1 Introduction 57
5.2 Synthesis and Structural Analysis 57

6 Results and Discussion 63
6.1 Comparison by Coordination Geometry 64
6.2 y Ligands 67


VI 7 Summary 70

8 Experimental Section 75
8.1 General 75
8.2 Ligand Synthesis 75
8.3 Complex Synthesis 84

9 Appendix 93
9.1 NMR-Spectra 93
9.2 Crystal Structures – Selected Data 123
9.3 List of Publications 133

10 Acknowledgement 134


Supporting Information (1 CD, ca. 180 MB, only available for group members):
Table of Contents
Thesis (pdf-file)
Crystal Structures (cif-files)
CD Spectroscopy (txt-files)
UV Spectroscopy (Excel-files)
NMR Spectroscopy (Bruker files)
Graphics (various file types)
References (where available, pdf-files)










VII











VIII 0. Preface

Symmetry is one of the most ubiquitous phenomena in our life. Normally, we are so
used to it that we are often not even aware of the impact it has. For example,
symmetry is often associated with beauty, most of the time unconsciously. This is
true not only regarding works of art like Leonardo da Vinci´s “Vitruvian” or the Taj
Mahal (Figure 0.1), but also with respect to the attractiveness of a person.

Figure 0.1. Leonardo da Vinci´s “Vitruvian” and the Taj Mahal

Besides this, symmetry is also a very successful design principle of life in general.
There must be a reason why evolution chose many living things to be symmetric.
Almost every higher organsim exhibits, at least on a macroscopic level, mirror-image
shape. Nobody wonders, of course, why we have two eyes, two ears or two hands.

Figure 0.2. Symmetric Eastern Tiger Swallowtail

Nevertheless, the existence of a mirror-image relationship implies also a very subtle
form of symmetry, namely chirality. The fact, that things can be mirror-images, but
not superimposable, is an every day phenomenon. For example cars, one
1“enantiomer” of which is driving in left-hand traffic countries like the UK, the other one
on the roads of the rest of the world. Or our own body, where normally only one chiral
form is observed, namely those with the hearts on the left side. This brings us to an
astonishing phenomenon in living nature: the homochirality of life.
The “enantiopurity” of humans on a macroscopic level is reflected also in the world
of submiscroscopic dimensions. In general, nature has chosen to predominantely
have one form of chiral molecules. That is why (L)-amino acids or (D)-sugars are
among the most important building blocks for the generation of living systems. Not
only on a molecular, but also on a higher level chirality can be found e.g. in α-helices
of proteins or double-stranded DNA (Figure 0.3).


Figure 0.3. Chiral helices in nature: DNA-model and protein structure

The question of homochirality is probably closely connected to the origin of life itself.
Why nature was able to prefer only one form of enantiomers is still far from being
completely understood, especially because in classical physics it was long believed,
that the equivalence of left and right is a given thing and this was expressed in the
conservation law of parity. Only in the second half of the last century, first steps to
unravel this mystery were made. An important milestone was the spectacular finding
of Yang and Lee in 1956 (Nobel price 1957), that parity is not conserved in the β-
60 [1]
decay of Co. They showed, that in principle left and right need not be equal. And
indeed, nowadays it is possible to determine energy differences of enantiomeric
[2]molecules resulting from parity violation. Nevertheless, the effects are normally too
small to be observable, even on a microscopic level. Since Soai´s report, however,
on an autocatalytic system (Scheme 0.1) that creates enantiopure molecules from
almost racemic mixtures in the 90´s of the last century, we have an impression of
2