Organometallic ChemistryCHEM 310, Spring 2009
Lectures:Monday, Tuesday and Friday
Course Instructor : G. Maguireoffice: RM 329email: [email protected]. 1113
Course Evaluation:Tests 10%Practicals 25 % Final Exam 65 %
Course outline (first half):
Organometallics:
1. Introduction (types and rationale)
2. Molecular orbital (bonding) of CO, arrangement “in space”or ligand types (hapticity)
3. 16 and 18 electron rule (learning to count)
4. Synthesis, steric effects and reactivity - Wilkinsons catalyst (part 1)
5. Characterisation IR nmr etc.
6. Applications (oxidative addition β elimination)
7. Transition metals in biology
Course objectives:
To recognize organometallic ligands and compounds Knowledge of fundamental organometallic reactionsKnowledge of a variety of organometallic based catalytic reactions, including a mechanistic understanding including enzymatic reactions
To describe the synthesis and general properties of organometallic compounds
An introductory understanding of Bio-inorganic chemistry
Learning outcomes:
On completion of this unit, you should be able to/have:
What is organometallic chemistry?
Chemistry: structures, bonding and properties of molecules.
Organometallic compounds: containing direct metal-carbon bonds. Either σ or π bonds can occur
Main group:
(AlMe3)2
Structuresσ bonds and 3c-2e (or even 4c-2e) bonds
Chem 210
Synthesisthe first M-C bond
Reactivitynucleophilic and basicauxiliaries in organic synthesissource of organic groups for transition metals
Strong preference for σ-donor groups but Cp is often π-bound (deceptively like with transition metals)
Electropositive metals: often 3c-2e or 4c-2e hydrides/alkyls
Cp2Mg Cp2Fe
(Me3Al)2(MeLi)4
As a Nucleophile
Addition to polar C=X bonds(C=O, C=N, CºN)
Substitution at sp2 carbon(often via addition)
R MOδ+
O
R
M
R MO
OR'δ+
O
OR'R
M O
R- MOR'
Substitution at sp3 carbon does occurbut is far less easy and often has a multistep
mechanism
Substitution at other elements:often easy for polar M-X bonds(Si-Cl, B-OMe)
MeMgBr + B(OMe)3 BrMgMe
OMeB(OMe)2 MeOMgBr + MeB(OMe)2 Me3B
As a baseMore prominent in polar solvents think of free R- acting as base
Elimination
mechanism can be more complex than this
Metallation
chelate effect more important than inductive effect!
R M
H
X+ RH + MX
R MMe2N
H
Me2N
M
+ RH
β-hydrogen transfer
mainly for Al:for more electropositive elements, deprotonation and nucleophilic attackare fasterfor less electropositive elements, often no reaction
Al H
O OHAl
2
3
3
Chemistry: structures, bonding and properties of molecules.
Transition metal compounds
Some compounds do not contain metal-carbon bond, but they are usually included in the field of organometallic chemistry. They include:
• Metal hydride complexes, e.g.
• N2-complexes, e.g.
• Phosphine complexes, e.g.
In general, metals in organometallic compounds include:
• main group metals• transition metals • f-block metals
In this course, transition metals are our main concern.
Exercise. Which of the following compounds is an organometallic compound?
a) OCH3
TiCH3O OCH3
OCH3
b)
NH3
CuH3N NH3
NH3
2+
Cl Pt
Cl
Clc) CH2
CH2
-
d)O Pt O
O
O
Me
Li
Li
Li
MeMe
Me
Lie) CoCo
Co
P
Co
P COCO
COCO
OC
OC
OCOC
C O
CO
Ph
Ph
f)
A brief history of organometallic chemistry
1) Organometallic Chemistry has really been around for millions of years
Naturally occurring Cobalimins contain Co—C bonds
Vitamin B12
2) Zeise’s Salt synthesized in 1827 = K[Pt(C2H4)Cl3] • H2OConfirmed to have H2C=CH2 as a ligand in 1868Structure not fully known until 1975
3) Ni(CO)4 synthesized in 1890
4) Grignard Reagents (XMgR) synthesized about 1900
Accidentally produced while trying to make other compoundsUtility to Organic Synthesis recognized early on
5) Ferrocene synthesized in 1951Modern Organometallic Chemistry begins with this discovery (Paulson and Miller)
1952 Fischer and Wilkinson
Nobel -Prize Winners related to the area:
Victor Grignard and Paul Sabatier (1912)Grignard reagent
K. Ziegler, G. Natta (1963) Zieglar-Natta catalyst
E. O. Fisher, G. Wilkinson (1973) Sandwich compounds
K. B. Sharpless, R. Noyori (2001) Hydrogenation and oxidation
Yves Chauvin, Robert H. Grubbs, Richard R. Schrock (2005) Metal-catalyzed alkene metathesis
Common organometallic ligands
M H M C M CC M M
HH
MHX
M
M
M PR3
M CO M CNR
M CS M NO
M N2
M M MM
M
M C
M C
Why organometallic chemistry ?a). From practical point of view:
* OMC are useful for chemical synthesis, especially catalytic processes, e.g. In production of fine chemicals
In production of chemicals in large-scalereactions could not be achieved traditionally
* Organometallic chemistry is related to material sciences. e.g. Organometallic Polymers
Pt CPBu3
PBu3
C C Cn
Pt CPBu3
PBu3
C C C
n
Small organometallic compounds: Precursors to films for coating (MOCVD)
(h3-C3H5)2Pd -----> Pd film
CH3C≡C-Au-C≡NMe -----> Au film
Luminescent materials
* Biological Science. Organometallic chemistry may help us to understand some enzyme-catalyzed reactions.
R
H
H
R
e.g. B12 catalyzed reactions.
b). From academic point of view:* Organometallic compounds display many unexpected
behaviors- discover new chemistry- new structures e.g.
MM
M
H
HM
H
SiR3M
M C M CM
C C C C
H3N: M
New reactions, reagents, catalysts, e.g.Ziegler-Natta catalyst, Wilkinson catalystReppe reaction, Schwartz's reagentSharpless epoxidation, Tebbe's reagents………………..