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Triply-Bonded Dimolybdenum(III) Hexaalkoxides Towards Model Catalysts [Elektronische Ressource] / Jian-Gong Ma. Betreuer: Matthias Driess

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Triply-Bonded Dimolybdenum(III) Hexaalkoxides Towards Model Catalysts vorgelegt von M. Sc. Chemie Jian-Gong Ma aus Jilin (China) Von der Fakultät II – Mathematik und Naturwissenschaften der Technischen Universität Berlin Institut für Chemie zur Erlangung des akademischen Grades Doktor der Naturwissenschaften - Dr. rer. nat. - genehmigte Dissertation Promotionsausschuss: Vorsitzender: Prof. Dr. Reinhard Schomäcker (TU Berlin) 1. Gutachter: Prof. Dr. Matthias Driess (TU Berlin) 2. Gutachter: Prof. Dr. Thomas Braun (HU Berlin) Tag der wissenschaftlichen Aussprache: 27-04-2011 Berlin 2011 D 83 DISSERTATION by M. Sc. Chemistry Jian-Gong Ma from Jilin (China)J.-G. Ma, Y. Aksu, L. J. Gregoriades, J. Sauer, M. Driess, “Activation of C–H Bonds Mediated by Mo ≡Mo Moieties in Heterobimetallic Zn/O/Mo Clusters”, Dalton Trans. 2010, 39, 103. J.-G. Ma, S. Krackl, Y. Aksu, M. Driess, “Facile Access to Homo- and Heteroleptic, Triply-Bonded Dimolybdenum Hexaalkoxides with Unsaturated Alkoxide Ligands”, Eur. J. Inorg. Chem. 2011, 11, 1725. The work described in this thesis has been carried out under the guidance and supervision of Prof. Dr. Matthias Driess at the Institut für Chemie der Technischen Universität Berlin between February 2007 and February 2011. I would like to give my sincere appreciation to Prof. Dr.

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Triply-Bonded Dimolybdenum(III) Hexaalkoxides Towards
Model Catalysts

vorgelegt von
M. Sc. Chemie
Jian-Gong Ma
aus Jilin (China)

Von der Fakultät II – Mathematik und Naturwissenschaften
der Technischen Universität Berlin
Institut für Chemie
zur Erlangung des akademischen Grades

Doktor der Naturwissenschaften
- Dr. rer. nat. -
genehmigte Dissertation

Promotionsausschuss:

Vorsitzender: Prof. Dr. Reinhard Schomäcker (TU Berlin)
1. Gutachter: Prof. Dr. Matthias Driess (TU Berlin)
2. Gutachter: Prof. Dr. Thomas Braun (HU Berlin)

Tag der wissenschaftlichen Aussprache: 27-04-2011

Berlin 2011
D 83 DISSERTATION










by
M. Sc. Chemistry
Jian-Gong Ma

from Jilin (China)J.-G. Ma, Y. Aksu, L. J. Gregoriades, J. Sauer, M. Driess, “Activation of C–H Bonds
Mediated by Mo ≡Mo Moieties in Heterobimetallic Zn/O/Mo Clusters”, Dalton Trans.
2010, 39, 103.

J.-G. Ma, S. Krackl, Y. Aksu, M. Driess, “Facile Access to Homo- and Heteroleptic,
Triply-Bonded Dimolybdenum Hexaalkoxides with Unsaturated Alkoxide Ligands”,
Eur. J. Inorg. Chem. 2011, 11, 1725.
The work described in this thesis has been carried out under the guidance and
supervision of Prof. Dr. Matthias Driess at the Institut für Chemie der Technischen
Universität Berlin between February 2007 and February 2011.


I would like to give my sincere appreciation to Prof. Dr. Matthias Driess for his
continuous guidance, suggestions, discussion and encouragement throughout the
course of my thesis.
I am grateful to Prof. Dr. Thomas Braun for his acceptance of the second
commentatorship.
I am grateful to Prof. Dr. Reinhard Schomäcker for his acceptance of the chairman.
I would like to thank Dr. Yilmaz Aksu for his help, suggestions and stimulating
discussions during the course of my Ph. D work.
I owe my special thanks to my colleague Dipl. Chem. Sebastian Krackl for his
friendship and help. In addition, I am very grateful to Dr. Shenglai Yao, Dr. Yun
Xiong and Dipl. Chem. Wenyuan Wang for their help during my stay in Berlin. Also I
want to say thanks to all the members in the research group of Prof. Driess for their
help and kindness.
Acknowledgements are given to Prof. Dr. Joachim Sauer and Dr. Laurence J.
Gregoriades for cooperations and DFT calculations.
Last but not least, acknowledgements are given to Ms. Marina Borowski and Dr.
Elisabeth Irran for X-ray crystal structure determinations and solutions, Ms. Sigrid
Imme for CHN and IR measurements, Dr. Heinz-Jürgen Kroth, Dr. Jan-Dirk Epping
and Mr. Manfred Dettlaff for NMR measurements.
I heartfully thank my parents, Prof. Dr. Peng Cheng and my wife Yiwei Lv for years
of selfless support and encouragement.
This work was supported by the Cluster of Excellence “Unifying Concepts in
Catalysis” sponsored by the Deutsche Forschungsgemeinschaft (DFG). TABLE OF CONTENTS
1. INTRODUCTION.................................................................................................... 1
2. MOTIVATION ......................................................................................................... 9
3. RESULTS AND DISCUSSION ............................................................................. 11
3.1 Synthesis and Characterization of Homoleptic Triply-bonded Dimolybdenum Complexes
Mo L (L = NMe , NEt and OR) .................................................................................................... 11 2 6 2 2
3.2 Heteroleptic Triply-bonded Dimolybdenum Complexes .................................................................. 18
3.2.1 State of Knowledge ................................................................................................................ 18
3.2.2 Synthesis of the Heteroleptic Triply-bonded Dimolybdenum Hexaalkoxide
tMo (O Bu) (ONe) (7) ........................................................................................................... 19 2 2 4
t3.2.3 Molecular Structure of Mo (O Bu) (ONe) (7) ....................................................................... 23 2 2 4
3.3 Selective Oxidation of the Homoleptic and Heteroleptic Triply-bonded Dimolybdenum
Hexaalkoxides ................................................................................................................................. 25
3.3.1 State of Knowledge ................................................................................................................ 25
3.3.2 Oxidation of the Homoleptic Complex Mo (ONe) (5) by DEHA ......................................... 28 2 6
t3.3.3 Oxidation of the Homoleptic Complex Mo (O Bu) (4) by DEHA ........................................ 34 2 6
3.3.4 Mechanistic Details of the Reaction between Mo (ONe) (5) and DEHA ............................. 37 2 6
V3.3.5 Molecular Structures of Mo (O)(ONe) ( μ -ONe) (8) and MoO (ONEt ) (11) .................. 40 2 5 2 3 2 2 2
V3.3.6 Theoretical Investigation of Mo (O)(ONe) ( μ -ONe) (8) ................................................... 42 2 5 2 3
t3.3.7 Oxidation of the Heteroleptic Complex Mo (O Bu) (ONe) (7) ............................................. 44 2 2 4
t3.3.8 Molecular Structure of Mo ( μ -O)( μ -ONe) (ONe) (O Bu) (12) .......................................... 45 2 2 2 2 4 2
t3.3.9 Theoretical Investigation of Mo ( μ -O)( μ -ONe) (ONe) (O Bu) (12) .................................. 47 2 2 2 2 4 2
3.3.10 Comparison of the Oxidation of the Homoleptic and Heteroleptic Triply-bonded
Dimolybdenum Complexes ................................................................................................... 49
3.3.11 Catalytic Activity of Mo (O)(ONe) ( μ -ONe) ( 8) and 2 5 2 3
tMo ( μ -O)( μ -ONe) (ONe) (O Bu) (12) .............................................................................. 49 2 2 2 2 4 2
3.4 Heterobimetallic Mo ≡Mo/O/Zn Clusters ......................................................................................... 53
3.4.1 State of Knowledge ................................................................................................................ 53
3.4.2 Synthesis of the Asymmetric Mo ≡Mo/O/Zn Clusters Containing a “MoO Zn ” Cubane ...... 54 4 3
i3.4.3 Molecular Structures of [Mo (MeZn) ( μ -Me)( μ -CH ) (OR) ] Clusters .............................. 58 2 6 2 3 2 2 7
3.4.4 Theoretical Investigation of [Mo (MeZn) ( μ -Me)( μ -CH ) (OR) ] Clusters ........................ 61 2 6 2 3 2 2 7
3.4.5 Synthesis of the Symmetric Mo ≡Mo/O/Zn Cluster ................................................................ 66
3.4.6 Molecular Structure of [Mo (MeZn) ( μ -CH )( μ -CH ) (OR) ] (15) ..................................... 70 2 6 2 2 3 2 2 6
3.4.7 Theoretical Investigation of [Mo (MeZn) ( μ -CH )( μ -CH ) (OR) ] (15) ............................. 71 2 6 2 2 3 2 2 6
3.5 Reduction of the [Mo ≡Mo] Center in Triply-bonded Dimolybdenum Hexaalkoxides and the
Synthesis of a Lewis-Base-Free Mo Mo/Li Cluster ..................................................................... 76
3.5.1 State of Knowledge ................................................................................................................ 76
3.5.2 Synthesis of the Lewis-Base-Free Heterobimetallic Mo Mo/Li Cluster ............................. 77
n3.5.3 Molecular Structure of Li Mo Bu (16) ................................................................................ 80 4 2 8
n3.5.4 Theoretical Investigation of Li Mo Bu (16) ........................................................................ 83 4 2 8
4. SUMMARY AND CONCLUSION ....................................................................... 86
5. EXPERIMENTAL SECTION .............................................................................. 92
5.1 General Procedures ........................................................................................................................... 92
5.2 Physical Measurements .................................................................................................................... 92
5.3 Starting Materials ............................................................................................................................. 93
5.4 Synthesis of the Mo (NR ) and Mo (OR) ...................................................................................... 94 2 2 6 2 6
t5.5 Synthesis of Mo (O Bu) (ONe) (7) ............................................................................................... 100 2 2 4
V5.6 Synthesis of Mo (O)(ONe) ( μ -ONe) (8) .................................................................................... 101 2 5 2 3
5.7 Synthesis of Mo(O)(ONe) (10) and Mo(O) (ONEt ) (11) ........................................................... 102 4 2 2 2
t5.8 Synthesis of Mo ( μ -O)( μ -ONe) (ONe) (O Bu) (12) ................................................................... 104 2 2 2 2 4 2
c5.9 Synthesis of [Mo (MeZn) ( μ -Me)( μ -CH ) (OR) ] (R = Ne (13), Hex (14)) ............................... 105 2 6 2 3 2 2 7
c5.10 Synthesis of [Mo (MeZn) ( μ -CH )( μ -CH ) (O Hex) ] (15) ...................................................... 107 2 6 2 2 3 2 2 6
n5.11 Synthesis of Li Mo Bu (16) ....................................................................................................... 108 4 2 8
6. REFERENCES ..................................................................................................... 109
7. APPENDIX ........................................................................................................... 116
7.1 Crystal Data and Refinement Details ............................................................................................. 116
7.2 Density Functional Theory (DFT) Calculations Data ..................................................................... 163
iiAbbreviations
ABBREVIATIONS

br broad IR infrared
nBu n-Butyl LUMOLowest Unoccupied
Molecular Obital
tBu tert-butyl M metal
B3LYP Becke’s three-parameter hybrid MHz Megahertz
functional using the Lee, Yang and
Parr correlation “functional”
Celsisus degree Mp melting point
ca. about m multiplet
Cp cyclopentadienyl Me methyl
calc. calculated min minute(s)
d doublet ml milliliter(s)
ρ density mmol millimole(ar)
DEPT Distortionless Enhancement by m/z mass/charge
Polarisation Transfer
DFT density functional theory MS mass spectrometry
δ chemical shift Ne neopentyl
EI electron impact ionization NMR Nuclear Magnetic
Resonance
Et ethyl Ph phenyl
equiv. equivalent(s) ppm parts per million
ig gram(s) Pr iso-propyl
h hour(s) R organic substituent
cHex cyclohexyl r. t. room temperature
Hz Hertz TMS tetramethylsilane
HOMO Highest Occupied Moleclar Obital t triplet
K Kelvin X halogen

iiiIntroduction
1. INTRODUCTION

Molybdenum exhibits a remarkable ability to form metal-metal bonds in most of
its oxidation states. Quite abundant molybdenum dimers and clusters, which contain a
Mo −Mo bond with bond-order ranging from 1 to 5, have been synthesized and
1,2 studied. A very attractive kind of these are triply-bonded dimolybdenum complexes
1a,2-7since they are very well established and show a rich chemistry. One of the main
systems described in the literature contains mono-anionic ligands in the form of
Mo L (L = R, OR, NR ...). The first confirmed structure of a triply-bonded 2 6 2
dimolybdenum complex is Mo (CH SiMe ) , which was reported by Wilkinson in 2 2 3 6
3 1971. The latter compound contains the shortest Mo −Mo triple-bond (2.167 Å)
known until now. The intermetallic distance of a Mo −Mo triple-bond falls within the
range of 2.167-2.263 Å, depending on the nature of the attached ligands. The
constitution of the Mo −Mo triple-bond in Mo L complexes can be described as 2 6
2
2follows: Letting the z axis be coincident with the Mo −Mo axis, both metal d Z
orbitals may interact to form σ and σ* Mo −Mo molecular orbitals. d and d may xz yz
3form π and π* orbitals. In oxidation state +3, each Mo atom has a d configuration and
2 4thus a Mo −Mo triple-bond with the configuration of σ π can be formed, as shown in
2Fig. 1.



Fig. 1. The constitution of the Mo −Mo triple-bond in Mo L complexes. 2 6

Among Mo L complexes, triply-bonded dimolybdenum hexaalkoxides, 2 6
Mo (OR) , have been reported to show a specifically rich and diverse chemistry, most 2 6
1Introduction
2,4-10of which were investigated in the groups of Chisholm and Cotton.
In solution, N- and/or P-containing Lewis base ligands (L) can associate to the
triply-bonded dimolybdenum hexaalkoxides, Mo (OR) , to give the corresponding 2 6
adducts in the form of Mo (OR) L, as illustrated in Scheme 1 (Lewis-base 2 6 2
association reaction).



Scheme 1. Adduct formation of triply-bonded dimolybdenum hexaalkoxides with N
and/or P-containing Lewis-bases L.

For instance, the compound Mo (ONe) (HNMe ) has been isolated during the 2 6 2 2
4synthesis of Mo (ONe) from Mo (NMe ) . A number of P-containing donor ligands, 2 6 2 2 6
such as PMe , PMe Ph, PPh and Me PCH CH PMe , have also been reported to 3 2 3 2 2 2 2
2coordinate to the Mo (OR) complexes. 2 6



Scheme 2. Mo −OR bond insertion reaction of triply-bonded dimolybdenum
hexaalkoxides with CO . 2

i tMo (OR) -type (R = Me Si, Pr, Bu, Ne) compounds can also react with CO via 2 6 3 2
2Introduction
5a Mo −OR bond insertion reaction in hydrocarbon solvents (Scheme 2), which results
in complexes of the type Mo (OR) (O COR) . A corresponding structure is shown in 2 4 2 2
5bFig 2.



t t 5b Fig. 2. Molecular structure of Mo (O Bu) (O CO Bu) .2 4 2 2

The relative progress of CO insertion depends on the type of the OR ligand and 2
i tfollows the order NeO > PrO > BuO, which may be accounted to the different steric
congestion of the attached substituents. The reverse reaction namely the loss of CO , , 2
have been observed at 340 K.



i i 6Fig. 3. Molecular structure of Mo (O Pr) (OC(O Pr)NPh) . 2 4 2

The reactions of triply-bonded dimolybdenum hexaalkoxides with alkyl- and
3