organometallic chemistry chem 310, spring 2009cheminnerweb.ukzn.ac.za/files/chem310part1.pdf · in...

Organometallic ChemistryCHEM 310, Spring 2009

Lectures:Monday, Tuesday and Friday

Course Instructor : G. Maguireoffice: RM 329email: maguireg@UKZN.AC.ZAext. 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………………..