History and Devt of Organometallic compounds.pdf

Organometallic chemistry is an important branch of chemistry
Organometallic compounds play crucial role in physiological and chemical reactions now a days

1. J
1 · 1 WHAT IS ORGANOMETALLIC CHEMISTRY?
Organometallic chemistry deals with molecules that contain a metal-carbon bond. While
many chemists prefer -to say that for a compound to be classified as an organometallic
compound, the type of metal-carbon bonding in a molecule should be covalent or partially
covalent in nature, the scientific community as well as journals publishing articles in
organometallic chemistry take a more liberal view. The leading journals of the field define
an 'organometallic, compound as one in which-there is a bonding :interaction (ionic or
covalent, localised or delocalised) between one or more carbon atoms of an organic group
or molecule and a main group,-transition, lanthanide or actinide metal atom (or atoms).
Following longstanding tradition, organic derivatives of the metalloids such as boron,
silicon, germanium, arsenic and tellurium are also included in this definition. It is also
understood that the element to which carbon is bound is more electropositive than carbon
in organometallic compounds.
Based on the periodic table, one can broadly classify organometallic chemistry further into
transition metal, main group metal and lanthanide/actinide based organometallics. Among
these the most well developed, mechanistically understood and widely utilised in catalysis is
transition metal organometallic chemistry. Therefore, the focus of this book will be mostly on
transition metal organometallic chemistry.
Traditional chemists do not agree to classifying metal cyanide complexes as organometallic
while many refer to molecules such as the well known Wilkinson's cata~yst as organometallic
even though such molecules lack the required metal-carbon bond. While the latter is formally
incorrect, it is convenient to use when the molecule in question has reaction chemistry that is
derived from or will lead to an organometallic intermediate/s or product/s.
The importance of organometallic chemistry lies in its diversity and versatility as an area
which bridges conventional organic and inorganic chemistry and provides a common platform
for organic and inorganic chemists to come together and derive the benefits of both fields. This
branch of chemistry plays a vital role in the economy of developed nations as about a third of all
chemicals produced nowadays use organometallic catalysis. The applications of organometallic

2. 2 Basic organometallic chemistry
compounds in organic synthesis, industrial catalysis and materials chemistry have increased the
importance of this branch of chemistry.
Interestingly, the way chemists look at organometallic compounds differs according to their
basic background. Both inorganic and organic chemists, who are the key players in this field,
agree that the industrial importance of homogeneous catalysts has played a very important role
in the development and application of organometallic compounds. ·I
1. 2 A BRIEF HISTORY OF ORGANOMETALLIC CHEMISTRY
Important developments and events in the history of organometallic chemistry are given below.
1760 Discovery of 'Cadets fuming liquid', the first main group organometallic compound. In
a Paris military pharmacy, Cadet, while working on inks based on cobalt salts prepared
from cobalt minerals containing arsenic, discovered a fuming liquid, also called cacodyl
(malodorous) oxide.
As
2
03 + 4 CH3COOK [(CH3)2AsfaO
1827 . Discovery of Zeise's salt, K[PtCl
3
C
2
H
4
], first transition metal organometallic compound.
W C Zeise, a Danish pharmacist, reflu4ed K
2
PtC1
4
in ethanol and obtained an unusual
compound which was called Zeise's_salt; it was characterised later as the first organ0metallic
olefin (n) complex. The choice of platinum was fortunate as many noble metal alkene
complexes are air and moisture stable.
K [ ~l>~-~~H2]
CH2
1849 Edward Frankland made diethylzinc. Frankland, who was a student of Robert Bunsen
(Marburg, Germany), while attempting to make ethyl radicals hit upon Et2Zn (a
pyrophoric liquid) and ethylzinc iodide (solid). Frankland also coined the term
'organometallic'.
3 C
2
H
5
1 + 3 Zn • (C2H5)2Zn + C2HsZnl + Znl2
1852 Frankland used methyl halides and sodium amalgam to make dimethyl mercury. Later
on, alkyl tra_nsfer reactions using R Zn and R Hg were used by many to make more
main group organometc;lllic compo~nds. In the same year Lowig and Schweizer in
Zurich prepared tetraethyllead using Na/Pb alloy and in 1863 Friedel and Craft used
alkylzinc reagents for making organochlorosilanes. .
2 CH3X + 2 Na/Hg • (CH3)2Hg + 2 NaX
SiCl4 + m/2 ZnR2 • RmSiCl4-m + m/2 ZnCl2
1868 Schiitzenberger made the first metal carbonyl compound, [PtCl/CO)]
2
•
PtC1
2
+ CO • [PtCl2(CO)fa + cis PtCl2(C0)2

3. Introduction 3
1890 Ludwig Mond, the founder of the British chemical company ICI made Ni(CO) , the first
binary metal carbonyl; it is used in the refining of nickel.
4
1899
1900
1912
1917
Ni + 4 CO ___ .,.. Ni(C0)4
1 bar, 25°C
colourless gas : bp 42°C
The Barbier reaction was introduced by Philippe Barbier, a teacher of Victor Grignard.
Although less verstile than the Grignard reaction, it allows the reaction to be carried out
in one pot and even in the presence of water.
Br i Zn/ THF/H20
I + / ""--/ "--..
,....,....,.~...., H NH4CI, 5 h
OH
Grignard replaces Zn with Mg in the Barbier reaction. The Grignard reagents are much
more versatile and have more applications than organozinc reagents.
0
~+
R/"--MgBr
MgBr +
---:X,R~ h~
V Grignard and P Sabatier received the Nobel Prize for the Grignard reagent and Sabatier's
method of hydrogenation-using metal powders.
Wilhelm Schlenk prepared the first alkyllithium derivatives by transalkylation of
organomercury compounds. The synthetic capabilities of lithium derivatives eventually
replaced Grignard reagents as the primary anionic reactive intermediates.
2 Li + R
2
Hg 2 Rli + Hg
2 Etli + Me2Hg 2 Meli + Et2HQ
1921 Thomas Midgley working for GE motors introduced tetraethyllead as an antiknock
additive in gasoline.
1930 K Ziegler introduced the pr.eparation of organolithium compounds by a simpler route
which was further finetuned by Gilman. This encouraged wider use of organolithium
compounds.
1938
2 Li + PhCH20Me
RX + 2 Li
PhCH2Li + MeOLi
R Li + LiX (most common procedur_e)
Otto Roelen discovered hydroformylation (the Oxo process), the first use of an
organometallic compound in homogeneous catalysis.
[Co]
+ H2 + CO
0
R~H

4. 4 Basic organometallic chemistry
1939 W Reppe discovered nickel catalysed acetylene trimerisation.
R
RY)'R
R~R
3 R-----==--R
[Ni]
R
1943 E G Rochow discovered the direct synthesis of organochlorosilanes which initiated the
large scale production of silicones.
2 CHsCI + Si (Cu) ---•-(CHs)2SiCl2 (~ 80%)
300°c
1951 Two groups independently prepared ferrocene and suggested a sigma bonded structure.
The sandwich strt1:cture was proposed by Wilkinson, Fisher and Woodward.
Fe~+ Cp
Miller, Teqboth and Tremaine
F~Gls + CpMgBr
Kei;l,IY and Pauson.
195S~ E ()_ ·Fisher and-W Hafner prepared bis(benzene)chromium by a rational synthesis
-although F Hein -had possibly made the same by a reaction of CrC13 and PhMgBr in
1955
1959
1919. -
I -
Cr
<©
K Ziegle~ and G Natta developed olefin polymerisation at low pressure using mixed metal
catalysts (transition metal halide /AlR
3
).
First stabilisation of cyclooutadiene by complexation to a metal.
[(C4Me4)NiCl2l2
1961 Discovery ofVaska's complex which reversibly binds oxygen.
trans lrCl(CO)(PPh3)2
1963 Nobel prize for Ziegler and Natta.
1964 E O Fischer prepared the first metal carbene complex.
co
oc, I /co /CH3
W=C
oc/6o bcH3
1

5. Introduction 5
1965 Wilkinson and Coffey used (PPh
3
)
3RhCl as a homogeneous catalyst in the hydrogenation
of alkenes.
1968 W~llia~ S Knowles discovered a~ymmetri~ catalysis, whereby complexes containing
chiral_ hgan~s catalyse the conversion of ac_hiral substrates to chiral products with high
enantlomenc excess. The first such system involves the asymmetric hydrogenation of a.-
acetamidocinnamic acid derivatives using a rhodium catalyst.
MeOX)k~ COOH Ho~COOH
I Rh(DIPAMAPt I ..:::· .
h NHAc -------11- h H
AcO H
2
, HsO+ HO NH2
L-DOPA
(S-DOPA)
1972 R F Heck discovered the palladium catalysed substitution of vinylic hydrogen atoms
with aryl halides which opens up diverse palladium based cata_lysis reactions in organic
chemistry.
1973 E O Fischer prepared the first metal carbyne complex.
QC CO ,,
1-Cr=C-R
oc/ bo
1973 Nobel Prize for E O Fisher and G Wilkinson for their work on metal san<;lwich
compounds.
1976 M F Lappert prepared the first main group element dimetallenes by making the first
tin-tin double bonded compound.
[(Me3Si)2CH]2Sn = Sn[CH(SiMe3)2l2
1979 Suzuki and Miyaura published their first paper on Suzuki coupling of aryl boronic acids
· using palladium catalysts.
Q-Q
R
1980 Walter Kaminsky made zirconocene based catalysts exclusively for iso and syndiotactic
polypropylene.
... Cl
'Cl
M ,..Cl
Me 'Cl
, 1981 Robert West made the first stable compound having a silicon-silicon double bond.
(1,3,5-Me3CsH2)4Si2

6. I
1.
I
I
6 Basic organometallic chemistry
1981 Richard Schrock discovered a molybdenum based catalyst for olefin metathesis.
N
· II H
Mo=C""
F3C'}-/
CF3
1991 J M Hawkins made the first fullerene based organometallic compound which was also
the first structurally characterised fullerene derivative C
60
(OsO
4
){4-t-BuPy)
2
• Later on,
a host of organometallic compounds with direct metal-carbon bonds with 11
2-bonding
were discovered.
1992
1997
-0X
o" );I -
lo=Os=o
/ '
o ~n
0x
Robert Grubbs prepared his ruthenium based olefin metathesis catalyst (first generation
Grubbs catalyst).
C C Cummins showed the C atom as a ligand in an organometallic compound.
1997 GM Robinson synthesised the salt Na
2
[ArGaGaAr] and postulated a gallium-gallium
triple bond.
2001 W S Knowles received the Nobel prize for asymmetric hydrogenation along with KB
Sharpless and R Noyori.
2002 E Nakamura prepared 'bucky ferroce~es' -molecular hybrids of ferrocene and fullerene
-by treatment of C
60
HMe
5
or C
70
HMe
3
with [FeCp(CO)
2
]
2
•

7. Me 0
,,,fi II
/c, /co
l;e, .,,Fe~
OC C
II
0
PhCN, 180 °C, 8 h
Introduction 7
2004 A Sekiguchi prepared the first Si-Si triple bonded molecule and carried out its structural
characterisation.
(Me3Si)2HC
_)-Si-.._ . /CH(SiMe3)2
Pri / Si==si............. . _
(Me3Si)2HC s~ iPr
CH(SiMe3)2
2004 E Carmona prepared the first Z!} (I) organometallic compound.
Zn2(Cp*)2
2005 Yves Chauvin (France), Robert H Grubbs (Caltech) and Richard R Schrock (MIT), USA
received the Nobel prize for olefin metathesis.
2005 Philip Power prepared the first stable organometallic compound with a possible quintuple
bond (five fold metal-metal bond)
Ar-Cr Cr-Ar
2006 Peter C Vollhardt prepared hexaferrocenyl benzene (thought of as an impossible
molecule).
0-Fe
F~
Q
1 1 IAADnDTA1Jrs:-ns:-0Rr.ANOMF'TAI I IC" COMPOUNDS