Homoleptic complexes of group 9 and 10 transition metals with phosphine functionalized N-heterocyclic carbe ligands [Elektronische Ressource] / von Aziza A. Ahmida

Uniac210

Informations

• Publié par: universitat_paderborn
• Publié le: 01 janvier 2009
• Nombre de lectures: 34
• Langue: English
• Poids de l'ouvrage: 3 Mo

Extrait

Anorganische Chemie


Homoleptic complexes of group 9 and 10 transition metals with
phosphine-functionalized N-heterocyclic carbene ligands



Von der Fakultät für Naturwissenschaften
Department Chemie
Der Universität Paderborn


zur Erlangung des akademischen Grades eines
Doktors der Naturwissenschaften
Dr. rer. nat.
genehmigte Dissertation

von
Aziza A. Ahmida
aus Benghazi (Libyen)


Paderborn 2009
I






Date of submission: 23.11.2009
Date of examination: 18.12.2009

1. Referee: Prof. Dr. Gerald Henkel
2. Referee: PD. Dr. Hans Egold


The present work has been carried out during january 2005 and oktober 2009 at the
university of Paderborn, Faculty of Science, Department of Chemistry under
supervision of Prof. Dr G. Henkel.




II

Dedicated to

Spirit of my parents
My brothers and sisters













III Abstract
This dissertation describes the synthesis of phosphane functionalized imidazolium salts and their
use in the preparation of chelating mixed phoshane carbene ligands. The novel ligands were used
for the synthesis of homoleptic complexes of Rh(I), Ir(I), Ni(II) and Pd(II). The reactivity of the
Rh(I) and Ir(I) complexes with respect to small molecules has been investigated and the catalytic
activity of the Pd(II) complexes for Suzuki coupling has been explored as well.
Starting from ethylvinylimidazolium iodide and HPPh the imidazolium ligand precursors E5 and 2
E6 were synthesized in high yield. Their conversion to the aspired mixed phoshane carbene
ligand E7 has been accomplished in situ by deprotonation with K[N(SiMe ) ]. The degree of 3 2
conversion was almost quantitative as the reaction of the resulting solutions with CS giving the 2
thiocarboxylate E8 proved.
In situ generated E7 reacts with 0.5 equivalents [Rh(μ-Cl)(COD)] to give the novel homoleptic 2
Rh(I) complexes cis-E10, trans-E12, cis-E11, trans-E13 in high yields. All new complexes have
been structurally characterized by single crystal X-ray crystallography. NMR spectroscopic
stuidies of the dynamic behaviour of the complexes in solution have proved interconversion of
cis- and trans-isomer at elevated temperatures. A mechanism for this reaction has been proposed.
The oxidative addition of small molecules like O , S , CH I, I to cis-Rh(I) complexes E10 or 2 8 3 2
E11, respectively, afforded novel Rh(III) complexes E14, E15, E16, E17, E19. All new
complexes have been characterized by standard spectroscopic methods and single crystal X-ray
analysis. The complicated solution dynamics of the cis-peroxo-Rh(III) complex E14 was
31
explored in detail by P NMR-spectroscopy. The synthesis of novel cis-Ir(I) complex E20 has
been achieved by reaction of E7 with [Ir(μ-Cl)(COD)] . It reacts with H , O , S , CO, CH I, I 2 2 2 8 3 2
giving the novel Ir(III) complexes, E21, E22, E23, E24, E25, E26. Their structures are described
in detail. The synthesis of novel homoleptic trans-Ni(II) and Pd(II) complexes, E27, E28 and
their structural spectroscopic properties is described as well. The interconversion between cis and
31trans isomers of Pd(II) complex E28 at high temperature was again proved by P NMR
spectroscopy. The catalytic activity of trans-Pd(II) complex E28 with respect to Suzuki coupling
was surveyed.


IV Acknowledgements
First of all thanks to Allah who enabled me to complete this work. I would like to express my
deepest gratitude to my supervisor Prof. Dr. Gerald Henkel for giving me the opportunity of
joining his group and giving me his valuable guidance and continuous encouragement through
out this work.
From the depths of my heart I would like to express my thanks to PD Dr. Hans Egold for fruitful
discussions throughout this work and continous encouragement. He constantally supported this
work with both general advice and detailed comments and proof-reading.
I am grateful to Dr. Ulrich Flörke for his efforts of recording X-ray data and refining the X-ray
structures described in this thesis.
Furthermore, I am gratful to Mr. Jörg Schröder for his useful advice on special working methods
for experiments under inert gas atmosphere.
My gratitude goes to Mrs Karin Stolte for the countless hours of recording 2D NMR spectra and
to Mrs Maria Busse and Mrs Christiane Gloger for carrying out the elemental analyses.
My special thanks goes to my ever helpful colleague Mehmet Özer who always gave me
assistance with any computer related issues.
Also I would like to express my appreciation to Dr Ishtiaq Ahmed for proof-reading.
Thanks to all members of the working group of Prof. Dr. Gerald Henkel. Especially to my
colleague Muhammad Ayaz for the nice working atmosphere in the lab.
Thank you for all friends who have been there for me during my stay in Germany – especially
Intisar Elsharaa and Zuhl Gürbüz.
I gratefully acknowledge the financial support of Libyian Ministry of Higher Education and
German Academic Exchange Service (DAAD).
Finally, a big thank to my family for their invaluable support during these five years.





V Contents
1 Introduction 1
1.1 N-Heterocylic carbenes (NHC) 1
1.2 Hybridisation and structures 3
1.2.1 Singlet vs triplet carbenes 3
1.2.2 Electronic properties of different types of singlet carbenes 3
1.2.3 Mesomeric effects. 4
1.2.4 Carbene containing two π-acceptors substituents 5
1.2.5 Carbenes with two π-donor substituents 5
1.2.6 Carbenes with π-donor and π-acceptor substituents 7
1.3 Synthesis of free carbenes 8
1.4 NHC-carbene complexes 12
1.4.1 Classification of Fischer and Schrock-carbene complexes. 12
1.4.2 Comparsion between NHC-ligands and phosphine ligands 13
1.5 Synthesis of imidazolium salts as educts for the preparation of free
NHC ligands and NHC complexes 14
1.6 Synthetic routes to N-heterocyclic carbene complexes 16
1.6.1 Substitution reaction with free NHCs 16
1.6.2 Reactions of imidazolium salts with small metal complexes comprising
basic ligands 18
1.6.3 Reaction of transition metal complexes with electron rich olefines. 18
1.6.4 Unusual methods 19
1.6.5 Transmetallition reactions 20
1.7 N-heterocyclic carbenes in catalysis 22
1.7.1 Hydrosilylation 23
1.7.2 Hydrogenation 23
1.8 Cross-coupling in homogeneous catalysis 24
1.8.1 Songashira coupling 25
1.8.2 Kumada coupling (Grignard cross coupling) 26
1.8.3 Stille coupling 26
1.8.4 Heck coupling 27
VI 1.8.5 Suzuki coupling 28
2 Aim of work 32
3 Results and discusion 34
3.1 Synthesis of ligand 34
3.1.1 Ligand precursors 34
3.1.2 Properties of the imidazolium salts 35
3.1.2.1 X-ray crystallographic analysis of 3-[2-(diphenylphosphino)ethyl]-1-
Ethylimidazolium-hexafluorophosphate (E6) 37
3.1.3 In situ synthesis of free carbene 3-[2-(diphenylphosphino)ethyl]-1-
ethylimidazol-2-ylidene(E7) 39
3.1.3.1 Identification of imidazol-2-ylidendithiocarboxylate (E8) 39
3.1.3.2 X-ray crystallographic analysis of 3-[2-(diphenylphosphino)ethyl]-1-
ethylimidazol-2-dithiocarboxylate E8 40
3.1.3.3 Electrochemistry of 3-[2-(diphenylphosphino)ethyl]-1-
ethylimidazolium-hexafluorophosphate (E6) 44
3.2 Rhodium complexes 45
3.2.1 Syntheses and characterization of cationic cis and
trans-rhodium(I) complexes with E7 45
3.2.2 Single crystals X-ray structure analyses of cis-[Rh(EtImCH CH PPh ) ]X 2 2 2 2

(X = Cl (E10), PF (E11)) 47 6
3.2.3 Single crystal X-ray structure analyses of trans-[Rh(EtImCH CH PPh ) ]X 2 2 2 2
(X = Cl (E12), PF (E13)) 50 6
3.3 Equilibrium between cis and trans isomers at higher temperatures 54
3.4 Electrochemistry of cis-[Rh(EtImCH CH PPh ) ][PF ] (E11) 58 2 2 2 2 6
3.4.1 Electrochemistry of trans-[Rh(EtImCH CH PPh ) ]Cl, (E12) 59 2 2 2 2
3.5 Synthesis of peroxo complexes 60
2
3.5.1 Synthesis and dynamic behaviour of cis and trans-[Rh(η -
O )(EtImCH CH PPh ) ]X, (X = Cl (E14), PF (E15)) 60 2 2 2 2 2 6
2 + 3.5.2 X-ray crystallographic analyses of cis-[Rh(η -O )(EtImCH CH PPh ) ] 2 2 2 2 2
(E14A, X = Cl or PF ) 64 6
VII h
h
h
h
2 3.5.3 Single crystal X-ray structure analysis of trans-[Rh(η -O ) 2
(EtImCH CH PPh ) ][PF ] E15 66 2 2 2 2 6
3.6 Oxidative addition of small molecules viz, (S CH I, I ) to the cis-rhodium(I) 8, 3 2
complex E11 69
2
3.6.1 Synthesis and structure of cis-[Rh(η -S )(EtImCH CH PPh ) ][PF ] (E16) 69 2 2 2 2 2 6
2 3.6.1.1 Single crystal X-ray structure analyses of cis-[Rh( -S ) 2
(EtImCH CH PPh ) ][PF ]. (E16) 71 2 2 2 2 6
3.6.2 Synthesis of cis-[Rh(CH )(I)(EtImCH CH PPh ) ][PF ] (E17, E18) 74 3 2 2 2 2 6
3.6.3 Synthesis of cis-[Rh(Cl)(I)(EtImCH CH PPh ) ][I ], E19 74 2 2 2 2 3