Organometallic Chemistry
Dr. Marc Walter
Raum 149, Tel.: -5312, e-mail: [email protected]
http://www.tu-braunschweig.de/iaac/
10th
Ferrocene
Colloquium
Braunschweig 2012
Recent Nobel Prizes in the
area of homogeneous
catalysis
2001: Noyori, Sharpless,
Knowles
2005: Schrock, Grubbs,
Chauvin
2010: Heck, Negishi, Suzuki
I. What is “Organometallic Chemistry” ?
A: Complexes with Metal-Carbon--Bonds
B: Complexes with Metal-Carbon- -Bonds
II. Literature - Books
Elschenbroich, "Organometallchemie", Teubner 2003
Elschenbroich/Salzer, "Organometallics", VCH 1992
Shriver, Atkins, "Inorganic Chemistry", Oxford UP, 1999
Shriver, Atkins, Langford, "Anorganische Chemie", Wiley-VCH 1997
Huheey/Keiter/Keiter, "Anorganische Chemie", de Gruyter 1995
Cotton/Wilkinson/Murillo/Bochmann, "Advanced Inorganic Chemistry", Wiley 1999
Riedel (Ed.), "Moderne Anorganische Chemie", de Guyter1999
Carey/Sundberg, "Organische Chemie", VCH, 1995
Hegedus, "Organische Synthese mit Übergangsmetallen", VCH 1995
Togni/Halterman (Eds.), "Metallocenes", Wiley-VCH 1998
Cornils/Herrmann (Eds.), "Applied Homogeneous Catalysis with Organometallic Compounds", WileyVCH 2000
Beller/Bolm, "Transition Metals for Organic Synthesis", Wiley-VCH 1998
Wilkinson/Stone/Abel (Eds.), "Comprehensive Organometallic Chemistry II", Pergamon Press 1995
Brauer/Herrmann (Eds.), “Synthetic Methods of Organometallic and Inorganic Chemistry (8 Volumes,
Thieme, Stuttgart, 1996)
Other Resources
Monographic-Series “Advances in Organometallic Chemistry”
Monographic-Series “Topics in Organometallic Chemistry”
Journals “Organometallics"
Journals “Journal of Organometallic Chemistry"
R. Tereki, "The Organometallic Hypertextbook"
(http://www.ilpi.com/organomet/index.html)
III. History
L. C. Cadet (1760): During experimental work with invisible ink
cobalt salts containing arsenides (CoAs2-3, CoSAs)  formation of
"Dikakodyl" As2Me4 and Dikakodyloxide
Me2As-O-AsMe2
W. C. Zeise (1827): 1st organometallic transition metal complex
contested by J. Liebig: Liebigs Ann. Chem. 1837, 23, 1
William Christopher Zeise
(1789 – 1847)
Molecular structure of
K[PtCl3(C2H4)]H2O
(Inorg. Chem. 1975, 14, 2653)
M. P. Schützenberger (1868): 1st transition metal carbonyl
Classical „not classical" metal carbonyl
 CO as an almost pure -Donor
L. Mond (1890): 1st Binary Transition metal carbonyls
Accidental discovery during attempts to prepare Ammonia-Soda
(Solvay-procedure) by traces of CO decomposition on Nickel
valves. Back reaction affords high purity Nickel
100th Birthday of Metal carbonyls:
J. Organomet. Chem. 1990, 383, 1
Ludwig Mond
(1839 – 1909)
W. Hieber (ab 1928): Development of the chemistry of metal carbonyls
Miller, Tebboth, Tremaine (1948):
Walter Hieber
(1895 – 1976)
Kealy, Pauson (1951):
H
suggested structure:
Fe
H
bereits 1901 (J. Thiele):
Preparation of K+(C5H5)-
1952:
G. Wilkinson, R. B. Woodward
"Sandwich-Structure"
E. O. Fischer
"Double-Cone Structure"
Beginning of modern organometallic chemistry:
- Enormous interest in the last 50 years
- Large structural variety due to different geometries
- Various bonding situations
- Economic interest  homogeneous and heterogeneous
catalysis
- Organometallic chemistry in Organic Synthesis
50th Birthday of Ferrocene:
J. Organomet. Chem. 2002,637-639, 1
1973:
Nobel prize for E. O Fischer and G. Wilkinson
An organometallic bond in everyday life (until recently)
200-D-Mark-Schein mit Paul Ehrlich und Salvarsan
HO
As
As
H2N
OH
NH2
Salvarsan
IV. General Trends for the Transition Metals
Early Transiton Metals
low electronegativities
higher oxidation states
“harder” metal centers
OXOPHILLIC!!
Late Transition Metals
higher electronegativities
lower oxidation states
“softer” metal centers
V. The Bonding in Transition Metal Complexes
9 valence orbitals are available for bonding with organic molecules (ligands):
(n-1) dxz dxy dyz dx2-y2 dz2 (n) s px py pz
Only partial occupation:
Empty orbitals  Metal as an Electron acceptor
Occupied Orbitals  Metal as an Electron donor
(Note: the shading represents occupied orbitals, not the phase!)
3d-Orbitals
Donor/Acceptor-Synergy:
- -Donor bond
s, pz, dz2-AO‘s
(o. Hybride)
s, pz-AO‘s (e.g. PR3, X-)
*-MO‘s (e.g. CO)
-MO‘s
(e.g. C5H5-, Alkene, Alkyne)
dxz, dyz, px, py-AO‘s
(o. Hybrid)
px, py-AO‘s
(e.g. X-, OR-, NR2-)
-MO‘s
(e.g. CO, C5H5-, Alkyne)
- -Donor bond
- -Backbonding
dxz, dyz-AO‘s
(o. Hybride)
px, py, dxz, dyz- AO‘s
(e.g. carbene, PR3)
*-MO‘s
(e.g. CO, alkene, alkyne)
-MO‘s (e.g. H2)
- -Backbonding
dxy, dx2-y2- AO‘s
*-MO‘s
(e.g. C5H5-, Alkyne)
(in addition, also -bonding, e.g. in C8H82--complexes)
Electroneutrality principle:
The metal tries to be uncharged (as a rule of thumb).
0
W(CO)6
+6
W(CH3)6
CO as (weak) -Donor/strong -Acceptor
CH3 as stronger -Donor/weaker -Acceptor
See also for example
[CoL6]3+ L = NH3, F- ...
strongly electronegative Donor atom
Coordination number: 2-8 (4-6 most common)
X see: Angew. Chem. 1994, 106, 2515
18-Electron-Rule: The most important rule, in order to measure the stability of organometal
transition metal complexes; 9 fully occupied orbitals
Compare to the octet rule for main group metals
 TM-d-Electrons +  Bonding electrons = 18 Valence electrons
How to count electrons?
Ni(CO)4
d10 + 4x2 = 18 VE
Fe(CO)5
d8 + 5x2 = 18 VE
Cr(CO)6
d6 + 6x2 = 18 VE
There are two different counting conventions (note these are only formalisms):
Covalent Counting Model
(Neutral Ligand-Method)
Ionic Counting Model
(Electron Pair-Method)
C5H5- 6
C5H5
2 CO 4
2 CO 4
Cl-
Cl
2
5
1
Fe(+II) 6
Fe(0) 8


18
Ionic Counting Model
18
Covalent Counting Model
C5H5- 6
C5H5
Fe(+II) 6
Fe(0) 8
C5H5- 6
C5H5
5


18
18
5
Experimentally found charge distribution: Fe+0,2/C5H5-0,1 strongly covalent;
contrast to: 2 NaCp + FeCl2  Cp2Fe + 2 NaCl
Odd number of bonding electrons  Metal-Metal-Bonding
Mn(0)
5 CO
M-M

Mn(0) 7
5 CO 10

17
OC
O
C
O
C
O
C
Fe
Fe
CO
C
C
O C
C
O
O
O
Fe2(CO)9
Fe(0)
3 CO
3 2-CO
M-M

8
6
3
1
18
7
10
1
18
x- (hapticity)  Number x the carbon atoms coordinated to the metal
x- (nature of bridging)  Number x bridging between metal atoms
Contributions of different ligands to the total electron number of a complex:
(Huheey, Keiter, Keiter, S. 741)
Bonding in metal carbonyl complexes using the VB-Theory:
OC
O
C
O
C
O
C
Fe
Fe
CO
C
C
O C
C
O
O
O
from: Riedel (Hrsg.),
"Moderne Anorganische
Chemie", S. 592
Why is the 18-electron rule obeyed in organometallic chemistry?
MO-Diagram for an octahedral complex ML6 (only -bonding):
t1u*
a1g*
np
dx2-y2, dz2,
ns
eg*
eg
o
t2g
(n-1)d
t2g
dxy, dxz, dyz
ligand field
theory
eg
6 -AO's
(6 LGO's)
t1u
a1g
at complete occupation of the a1g-, t1u-, eg- and t2g-levels 
18 valence-electrons
o is large for strong field ligands
(see spectrochemical series)
e.g. CO, PF3, RNC, Alkyl, Alkene, Alkyne, Arene
 Both good -donors and also good -/-acceptors
Why is CO a strong field ligand?
Aid for the construction of MO diagrams
Symmetry elements, from: Klapötke, Tornieporth-Oetting, “Nichtmetallchemie“, S. 35
Symmetry elements of s-, p- and d-orbitals depending on their point groups, from:
Shriver, Atkins, Langford, “Anorganische Chemie“, Anhang B4
(see also symmetry adapted orbitals/ligand group orbitals)
t2g
eg
Molecular Orbital Diagrams
for SF6
(without d-orbitals)
for transition metal complexes
(only -bonding)
12-22 VE
Schematic representation of d-orbital splittings in a metal -complex:
eg*
eg*
o
o
d
d
t2g
t2g
eg
eg
eg
small E between M- and Lorbitals
(strong -Donor)
 strong orbital interaction
 large d-orbital splittings
eg
large E between M- und Lorbitals
(strong -Donor)
 little orbital interaction 
small d-orbital splittings
- good -Donors  eg* strongly anti-bonding  empty
Schematic representation of d-orbital splitting at the metal through interaction
with a -acceptor ligand:
t2g*
-AO's
eg*
eg*
(LGO's)
o
o
t2g
t2g
Interaction with empty -orbitals
 stabilisation of the t2g-levels
 o < o
- good -Acceptors  t2g strongly bonding  fully occupied
Therefore for these ligands the 18-Electron-Rule is obeyed:
[V(CO)6]-, Fe(PF3)5, CpMn(CO)3, [Fe(CO)4]2-, Ni(CNR)4, HMn(CO)5
CpCo(CO)2, Cp2Fe, [Cp2Co]+, (C6H6)2Cr, [CpMo(CO)3]2
Exceptions due to steric considerations, e.g.:
V(CO)6, Ti(CH2SiMe3)4, Cp2ZrCl2, W(CH3)6
Why is the 18-electron rule in coordination chemisty frequently disobeyed?
Many exceptions, but here are two extreme examples:
Flouride is a good -Donor
 t2g is antibonding
 empty
A relatively weak -Donor
 eg* only weakly antibonding
 Fully occupied
Schematic diagram of the d-orbital splitting at the metal through interaction
with a -donor function:
eg*
eg*
o
o
t2g
interaction with filled  -orbitals
 destabilisation of the t2g-levels
 o > o
t2g*
-AO's
(LGO's)
t2g
MO-diagram for an octahedral complex ML6
only-bonding
only- and -bonding
from: Elschenbroich/Salzer, "Organometallchemie", S.228
-Ligand
orbital groups
-Ligand orbital groups
from: Riedel (Hrsg.), "Moderne Anorganische Chemie", S. 216
Early Transition Metals
Middle Transition
Metals
Late Transition
Metals
16e- and sub-16econfigurations are
common
Coordination
geometries higher than
6 relatively common
18e- configurations are
common
16e- and sub-16econfigurations are common
Coordination
geometries of 6 are
common
Coordination geometries of 5
and lower are common: d8 =
square planar