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Complexes of alkenes, alkynes, and dienes
Created by Margaret L. Scheuermann, Princeton University; Abby R. O’Connor, The College of New Jersey, [email protected].
Copyright Scheuermann and O’Connor, 2014. This work is licensed under the Creative Commons Attribution-NonCommercialShareAlike 3.0 Unported License. To view a copy of this license visit http://creativecommons.org/about/license/
History & Utility
First example
Popular starting materials and precatalysts:
W. C. Zeise, Annalen der Physik, 1831, 21, 497.
Review: Hunt. Platin. Met. Rev. 1984, 28, 76.
Catalytic intermediates:
Alkene hydrogenation^*
Alkene dimerization/ oligomerization/ polymerization^*
Olefin metathesis^*
Mizoroki-Heck^*
Wacker Oxidation^
Hydrofunctionalization- Hydroboration/ hydosilylation^/ hydrocyanation^/
hydroamination^/ hydroformylation^/ etc.
^ significant industrial use; * Nobel Prize
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z
x
Orbital Overlap- Octahedral Example
Olefin along z axis
y
Olefin
C-C σ*
Olefin along x (or y) axis
M-olefin σ*
M-olefin σ*
dx2-y2
dz2
M-olefin π*
M-olefin π
M-olefin π*
C-C π*
M-olefin π
C-C π
Dxy (or
dyz or
dxz)
dxz
(or dyz)
C-C σ
M-olefin σ
M-olefin σ
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Types of π-bound ligands
Extremes
Less backbonding
into π*… electron
poor metal center
More backbonding
into π*… electron
rich metal center
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Properties
Electron rich metal centers tend to form
more stable olefin complexes
• late metals
• Low oxidation states
• high d-electron counts
• low overall charge
Rotation around metal-olefin bond
Orientation determined by steric and electronic factors
Bond lengths and angles
NMR
•As backbonding increases so do geometry differences
•C-C bonds get longer
• When backbonding is minimal
(electron poor metal center) 1H and
13C shifts resemble free olefin
• sp2 becomes more sp3-like
• sp becomes more sp2-like
• can help relieve ring strain
Buchwald. JACS
1986, 165, 7441.
• When backbonding is significant
(electron rich metal center) 1H and 13C
resonances shift upfield- smaller δ
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Synthesis & Reactivity
Ligand substitution*
β-hydride elimination*
Displacement by ligand substitution*
Insertion*
α
β
R = H, alkyl, aryl
Reduction
* Often present in catalytic cycles
Nucleophilic attack*
(when metal center is a poor π donor)
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