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Midterm

CHEM 312 Study Guide - Midterm Guide: Ferrocene, Carbene, Bridging Ligand

by mss2

Department
Chemistry
Course Code
CHEM 312
Professor
C Murphy
Study Guide
Midterm

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Chem 312
Spring 2019
Exam III Review Sheet
Formulas you should memorize (in addition to ones from Exams 1 and 2)
k = A
o
-Ea/RT
Formulas you should be able to use but do not have to memorize
σ = e(nμ
e
+ pμ
h
)
Questions
Need to know Hieber Base Reaction? M-CO → MH2? L20 slide 11
assign ox number to this
Definitions and concepts to know
Carbene, carbyne, carbonyl, Cp, Cp*, hydride, ferrocene, metallacyclic intermediate in Grubbs/Schrock
catalysts
Carbene
Carbyne
Carbonyl
Good as a ligand because it is
Strong field, pi acceptor , 18 e- rule usually applies
Complexes are usually themo and oxidatively stable
Spectrally traceable
Commercially available
Can bind with different μ values
Terminal (1M), bridging (2M), facial (3M)
Bonding
CO weak sigma donor
CO strong pi acceptor (pi backbonding)
Cp
Cp*
Hydride
Huge range of acidity
Can measure equilibrium constant
Ferrocene

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good redox by 1 electron. Can go from eclipsed to staggered quickly
because low ΔG
Easy to make
FeCl2 + 2NaCp → FeCp2 + 2 NaCl (in THF)
There can be reactions on the ring that will shift a ring to the side, allowing for a metal to
bind another ligand
Metallacyclic intermediate in Grubbs/Schrock catalysts
μ bridging ligand nomenclature
μ tells you how many metals the ligand is bound to.
the wavenumber of the CO stretch decreases as μ increases
because more pi backbonding into pi* orbital, which weakens the pi bonds. When these bonds
are weakened, they start to have more single bond character and the wavenumber decreases
SAME FOR L LIKE OLEFINS
THIS IS OPPOSITE FOR M-C STRETCHES??
Hapticity (η) ligand nomenclature
η tells how many atoms in the ligand is coordinated
Oxidative addition, reductive elimination, ligand substitution, migratory insertion
Oxidative addition
Add 2 coordination sites to the M complex, increase the oxidation number of the M by 2.
The ligands don't have to go on cis
Favored for
Electron rich, low valent M
Sterically unhindered M
Low X-Y BDE
Easily dissociated L
Can use light to pop off a L to open up a coordination site
Reductive elimination
Favored for
Electron rich ligands
Electron poor metals
Bulky ancillary ligands
Cis disposition of the eliminating ligands is requirement
First step can be ligand dissociation
Ligand substitution
Can be
Associative - like SN2
There needs to be an intermediate where the leaving L is leaving and the
incoming L are attached at the same time.

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Rate dependent on the nature of the incoming L
Dissociative - like SN1
The ligand leaves all by itself and then the incoming L can associate
Rate independent of the nature of the incoming L
For 14 or 16 e- complexes, associative and RDS is ligand association
Migratory insertion
1,1 and 1,2
1,1 - L at 1 position jumps onto another ligand at the 1 position
1,2 - L at position 1 jumps to a 2 position
Migration
Insertion
Usually can't tell which it is.
Beta hydride elimination
Must be H on beta carbon
M needs to have an available site cis to the alkyl group
Catalyst, both homogeneous and heterogeneous, activation energy, TON and TOF
Catalyst: lower the activation energy of a reaction without being used as a reactant itself
Homogeneous catalysts: are in the same phase as the reactant particles
More reactive/higher reaction rates
Limited by lower reaction temperatures
Heterogeneous catalyst: are in a different phase than the reactant particles
Product/catalyst are separated easily
More stable and have a higher reaction temperature
Activation energy: the minimum quantity of energy which the reacting species must possess in
order to proceed from reactants to products
Lowered by the catalyst (the lower the activation energy, the faster the reaction
proceeds)
TON (turnover numbers or turnovers): the number of cycles for which the catalyst is active
(converting reactants to products) before it dies
Units: moles of product per moles of catalyst
TOF (turnover frequency): the rate of catalyzed reactions per mole of catalyst
Units: moles of product per moles of catalyst per time
Hydrogenation: converting liquid vegetable oil into solid or semi-solid fats
Example: margarine
Physisorption and chemisorption
Physisorption: when the adsorbate is barely disturbed by absorption
Comes into close contact with the surface (example: van der waals)
Is higher in energy and further from the surface
Chemisorption: There is a chemical reaction that takes place between the
surface and the adsorbate resulting in the formation of a chemical bond
Forms a chemical bond to the surface
Is lower in energy and closer to the surface
Olefin metathesis, Haber-Bosch process, steam reforming, water-gas shift reaction
Olefins
Olefin metathesis: organic reaction that entails the redistribution of fragments of alkenes by the
scission and regeneration of C=C bonds
Creates fewer undesired by-products and hazardous wastes
Haber-Bosch process: a nitrogen fixation process (N
2
+ H
2
àNH
3
)
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