Tutorial II
(Organometallics and Catalysis)
Organometallic Chemistry
The chemistry of compounds that contain at least one metal–carbon bond.
Main Group Organometallic Compounds -
• R-Mg-X
• R-Li
• [(CH3)2As]2O
Transition Metal Organometallic Compounds -
• K[PtCl (C H )] Zeise's salt
3 2 4
• Ir(PPh3)3(CO)Cl Vaska’s complex
• (PPh3)3RhCl Wilkinson’s catalyst
• (Cp)2Fe Ferrocene
• R2CuLi Gillman reagent
F-block Organometallic Compounds -
• (C8H8)2U
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The rule is based on the fact that the valence orbitals of
transition metals consist of five d orbitals, one s orbital and
three p orbitals which can collectively accommodate 18
electrons as either bonding or nonbonding electron pairs.
When a metal complex has 18 valence electrons, it is said to
have achieved the same electron configuration as the
noble gas in the period.
Origin of 18 electron rule
• Inert gas configuration.
• No electron in the antibonding orbitals.
Complexes having π interaction
Electron Count
• To count electrons one must:
– note any overall charge on the metal complex.
– know the charges of the ligands bound to the metal center.
– know the number of electrons being donated to the metal
center from each ligand.
– Add up the electron counts for the metal center and ligands.
Electron Count
• Hence, it is unsaturated complex and undergo
reactions.
Problems
Q. Calculate the total valencne electrons in the
following complexes (a –c) and comment on stability
of the complexes:
Problems
Q. Calculate the total valencne electrons in the
following complexes (a –c) and comment on stability
of the complexes:
Problems
Q.For each of the given complexes (i-iii), (a) determine the
number of electrons; (b) Find out the oxidation state of the
metal, (c) count the total electron present in each complex.
Problems
Q. For each of the given complexes (i-iii), (a) determine the
number of electrons; (b) Find out the oxidation state of the
metal, (c) count the total electron present in each complex.
• Among the above complexes which one can act as oxidizing
agent?
Problems
Q. Determine the value of “n” in the following
stable organometallic complexes.
(a) Na2{Fe(CO)n}
(b) MnBr(CO)n
(c) RhBr2(CO)n(PPh3)2(CH3)
Problems
Q. Determine the value of “n” in the following
stable organometallic complexes.
(a) Na2(Fe(CO)n
(b) MnBr(CO)n
(c) RhBr2(CO)n(PPh3)2(CH3)
Ans: (a) n=4 (b) n=5 (c) n=1
Bonding mode in Metal-carbonyls
Important reactions in Organometallic Chemistry
Oxidative Addition
Reductive Elimination
Migratory Insertion Reaction
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Oxidative Addition Reaction
Addition of ligand occurs on the metal followed by the oxidation
of metal.
(Simple addition)
(Oxidative addition)
In oxidative addition reaction’s oxidation state, coordination
number and electron count of metal is increased by two units.
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Key points for Oxidative Addition Reaction :
The metal should have non-bonding electron density.
e.g.- TiCl4 will not undergo oxidative addition
reaction.
The two unit higher oxidation state of metal should be
stable and energetically accessible.
The metal should be coordinatively unsaturated.
e.g.- Square planer complexes will undergo fast
oxidative addition reaction in compare to
octahedral complexes.
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Stereo Chemistry of Oxidative Addition Reaction :
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Key point for Reductive Elimination Reaction :
The two eliminating groups must be cis in geometry
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Migratory Insertion Reaction
A cisoidal anionic and neutral ligand on metal complex couple
together to generate a new coordinated anionic ligand.
There is no change in oxidation state or d-electron count of the
metal center.
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Catalysis
The catalyst lowers the activation barrier for a transformation,
by introducing a new reaction pathway. However, it will not
affect the thermodynamics of the process.
Homogeneous Catalysis
Heterogeneous Catalysis
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Olefin Hydrogenation using Wilkinson’s Catalyst
• RhCl(PPh3)3 was the first highly active homogeneous
hydrogenation catalyst and was discovered by Geoffrey
Wilkinson.
Problems
Q. What are the expected products?
Ques – Calculate the total valance electrons for the following
complexes –
1. WMe6 (12 e-)
2. CH3Mn(CO)5 (18 e-)
3. [PtCl3(C2H4)]- (16 e-)
4. [Ir(PPh3)2(CO)Cl] (16 e-)
5. V(CO)6 (17 e-)
6. Rh(PPh3)3Cl (16 e-)
7. [(η5-C5H5)RuCl(CO)(PPh3)] (18 e-)
8. [W(CO)3(SiMe3)(Cl)(NCMe)2] (18 e-)
9. Pd(PPh3)4 (18 e-)
10. [(η5-Cp)2Ti(η1-Cp)2] (16 e-)
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Ques – Calculate the total valance electrons for the following
complexes –
1. [(η5-Cp)(η3-Cp)W(CO)2]
2. [WCl6]2-
3. [TcF6]2-
4. [OsCl6]2-
5. [PtF6]-
6. [Co(H2O)6]2+
7. [Ni(en)3]2+
8. [Zn(NH3)6]2+
9. [VCl6]2-
10.[Cr(NCS)6]3-
