Transcript No Slide Title

Standard Organometallic
Reaction Types
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Ligand dissociation/association
Insertion/elimination
Oxidative addition/reductive elimination
s-bond metathesis
Isomerization
Nucleophilic or electrophilic attack at metal
Nucleophilic or electrophilic attack at ligand
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Reaction Types
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Less Common Reaction Types
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Hapticity changes
Single-electron oxidation/reduction
Bond homolysis
Electrocyclic reactions
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Reaction Types
2
What else is there?
• Most organometallic reactions can be written
in terms of series of these standard reactions.
• Whether they really go like that is not always
certain.
• When looking for an acceptable mechanism,
try to restrict yourself to the "standard steps".
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Reaction Types
3
Ligand dissociation/association
• Electron count changes by -/+ 2
• No change in oxidation state
• Dissociation easiest if ligand stable on its own
(CO, olefin, phosphine, Cl-, ...)
• Steric factors important
M
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M
Br
Reaction Types
+ Br4
Insertion/elimination
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Migratory insertion!
The ligands involved must be cis.
Electron count changes by -/+ 2
No change in oxidation state
Olefins: 1,2-insertion, b-elimination
CO, RNC: 1,1-insertion, a-elimination
Et
Zr
Zr
Me
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Rh
Rh
CO
Reaction Types
Et
5
O
Oxidative addition/
reductive elimination
• Electron count changes by +/- 2
(assuming the reactant was not yet coordinated)
• Oxidation state changes by +/- 2
• Mechanism may be complicated
H
R3P
R3P
Rh
Me
PR3 H2 R3P
H
R3P
Rh
PR3 MeBr
R3P
Cl
R3P
Cl
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Rh
PR3
Cl
Br
Reaction Types
6
s-bond metathesis
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Requires an empty site
Electron count does not change
Oxidation state does not change
Can often be viewed as an acid-base reaction
Cp2Sc Me + H2
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Me
Cp2Sc H
H
Reaction Types
Cp2Sc
H + CH4
7
Isomerization
• Movement of ligands around the metal
• No change in electron count, oxidation state
• Common for 3- and 5-coordinate species,
less usual for 4-coordinate complexes,
hardly ever for 6-coordinate octahedral
complexes
Me
Me
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Reaction Types
8
Nucleophilic or electrophilic
attack at metal
• Nucleophilic:
– requires an empty site
– is basically ligand association
• Electrophilic:
– requires a metal-centered lone pair
– no change in electron count
– usually +2 in oxidation state
Cp2WH2 + H+
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Reaction Types
Cp2WH3+
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Nucleophilic or electrophilic
attack at ligand
• Nucleophilic:
– requires an electron-poor ligand atom
(acidic proton, coordinated C=X bond)
Cl
• Electrophilic:
H2O
Pd
Cl
Cl
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+ OH
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H2O
Pd
Cl
OH
– requires a ligand-centered electron pair
(usually a lone pair, ligand p-bond, or M-C s-bond)
– often reduces electron count by 2
Cp2ZrMe2 + Ph3C+
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Reaction Types
Cp2ZrMe+ + Ph3CMe
10
Hapticity changes
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Often indenyl, dienes; sometimes for Cp
Changes electron count
Does not change oxidation state
Is usually a way for a system
to "make room" for another reaction
or to avoid counts above 18-e
Mo CO
CO
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Reaction Types
Mo CO
CO
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Single-electron
oxidation/reduction
• Changes both electron count
and oxidation state by 1
• Usually by an added oxidant/reductant
or electrochemically
• Oxidized and reduced species typically differ
widely in reactivity
Cp2TiCl2
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Na
[Cp2TiCl2-]
Reaction Types
- Cl-
Cp2TiCl
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Bond homolysis
• Requires a weak M-C bond
• Typically for:
– heavier main-group metals
– first-row transition metals in high oxidation states
Bz2Hg
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
BzHg + Bz
Reaction Types
13
Electrocyclic reactions
• Can often be written as insertions
or oxidative additions
• Most common for complexes bearing two
coordinated alkenes or alkynes
and in olefin metathesis
• Usually change both electron count and
oxidation state
L2Ni
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Reaction Types
L2Ni
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