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Organometallic Chemistry
between organic and inorganic (?) 2/22/2019 Introduction to Organometallic Chemistry
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Why Organometallic Chemistry ?
Main use in organic synthesis and (homogeneous) catalysis. Using metals, you can make complicated organic structures that would be hard to make otherwise. This is because, compared to "standard organic chemistry", metals display new and unusual reaction types. To understand the "rules" you have to be able to "count electrons". The "18-electron rule"... 2/22/2019 Introduction to Organometallic Chemistry
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Introduction to Organometallic Chemistry
Organic Chemistry more or less covalent C-X bonds rigid element environments fixed oxidation states ?Organometallic Chemistry? Inorganic / Coordination Chemistry primarily ionic M-X bonds variable and often fluxional environments variable oxidation states 2/22/2019 Introduction to Organometallic Chemistry
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Organometallic Chemistry vs. Organic Chemistry
Many similarities Many differences Both can be “understood" You don’t have to learn everything by heart, but some basic knowledge is required to get anywhere. 2/22/2019 Introduction to Organometallic Chemistry
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Organometallic Chemistry
There are many metals ! The chemistry of Fe is not much more complicated than that of C, but after that there are 80 more metals... Generalization is important. We concentrate on the M side of the M-C bond, and on how to tune its reactivity. Applications: synthesis, catalysis, materials, pharmaceuticals. 2/22/2019 Introduction to Organometallic Chemistry
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Introduction to Organometallic Chemistry
2/22/2019 Introduction to Organometallic Chemistry
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Introduction to Organometallic Chemistry
Organic Chemistry Chemistry of C-X bonds C-C / C-H : nearly covalent Cd+-Xd- : polar (partly ionic) SN1, SN2 and analogous additions/eliminations Electrocyclic reactions Woodward-Hoffmann rules 2/22/2019 Introduction to Organometallic Chemistry
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Introduction to Organometallic Chemistry
Organic Chemistry Carbon is tetrahedral, trigonal or linear Reactive intermediates / transition states: 2/22/2019 Introduction to Organometallic Chemistry
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Organometallic Chemistry: Main group metals
s and p orbitals. 8-e rule, usually. Metal is the "d+" side of the M-C bond. "Umpolung" of the organic fragment. 2/22/2019 Introduction to Organometallic Chemistry
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Organometallic Chemistry: Main group metals
More electropositive and larger: higher coordination numbers, regardless of the number of electrons. “Early" groups and not very electropositive: lower coordination numbers. 2/22/2019 Introduction to Organometallic Chemistry
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Organometallic Chemistry: Main group metals
Multiple bonds relatively weak and reactive. C-C 85 C=C 150 N-N 40 N=N 100 P-P 50 P=P 75 2/22/2019 Introduction to Organometallic Chemistry
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Organometallic Chemistry: Transition metals
s, p and d orbitals 18-e rule, sometimes 16 e other counts relatively rare 2/22/2019 Introduction to Organometallic Chemistry
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Organometallic Chemistry: Transition metals
Metal is usually "d+" Metals are sterically saturated 2/22/2019 Introduction to Organometallic Chemistry
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Organometallic Chemistry: Transition metals
Often ligands capable of donating 2-8 electrons Preference for p-system ligands Bonds relatively weak Catalysis ! 2/22/2019 Introduction to Organometallic Chemistry
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“Forbidden” reactions ?
2/22/2019 Introduction to Organometallic Chemistry
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Reactivity of the M-C bond
Polar Þ reactive towards e.g. Water: Me3Al explodes with water; Me4Sn does not react. Oxygen: Me2Zn inflames in air; Me4Ge does not react. Carbonyl groups: MeLi adds at -80°C, Me3Sb not even at +50°C. 2/22/2019 Introduction to Organometallic Chemistry
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Oxidation and hydrolysis: large driving force
Al-C 65 As-C 55 Si-C 74 Al-O 119 As-O 72 Si-O 108 Al-Cl Si-Cl 91 2/22/2019 Introduction to Organometallic Chemistry
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Type of reactions in organometallic chemistry (1)
Ligand dissociation / coordination 2/22/2019 Introduction to Organometallic Chemistry
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Type of reactions in organometallic chemistry (2)
Metal as a ligand 2/22/2019 Introduction to Organometallic Chemistry
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Type of reactions in organometallic chemistry (3)
Insertion b-elimination 2/22/2019 Introduction to Organometallic Chemistry
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Type of reactions in organometallic chemistry (4)
Oxidative addition / Reductive elimination 2/22/2019 Introduction to Organometallic Chemistry
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Type of reactions in organometallic chemistry (5)
s-bond metathesis 2/22/2019 Introduction to Organometallic Chemistry
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Type of reactions in organometallic chemistry (6)
Redox reactions Homolysis 2/22/2019 Introduction to Organometallic Chemistry
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Type of reactions in organometallic chemistry (7)
Reactivity of coordinated ligands 2/22/2019 Introduction to Organometallic Chemistry
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Factors governing structure and reactivity of organometallic compounds
M-C, M-X bond strengths Electronegativity of M Number of (d) electrons Coordination number Steric hindrance 2/22/2019 Introduction to Organometallic Chemistry
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Trends in the periodic table
Main group metals: left and down: more electropositive down: higher oxidation states less stable Transition metals: middle: strongest preference for 18-e 2nd and 3rd row: strong preference for paired electrons (low-spin states) down: higher oxidation states more stable 2/22/2019 Introduction to Organometallic Chemistry
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Techniques of Organometallic Chemistry
Xray diffraction Þ structure Þ bonding NMR Þ structure en dynamic behaviour (calculations) IR MS EPR Not: GC LC 2/22/2019 Introduction to Organometallic Chemistry
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