What is ORGANOMETALLIC Chemistry ?
Strict Definition = Compounds containing metal-carbon bonds
(often extended to include M-Si, M-Ge, M-H etc. due to
similarities with M-C)
Tobin Marks
(Northwestern)
Br
OC
OC
Cl
CO
CO
Mn
Ni
Ta
CH3
Cl
Th
Cl
CO
C6 F5 B(C6 F5)3
Deryn Fogg
(U Ottawa)
Don Tilley
UC Berkeley
W
Cl
Cy 2
P
P
Cy2
Ru
Cl
Cl
Cl
Ru
ON
Cy2
P
P
Cy2
H
W
P
P
Peter
Legzdins
(UBC)
Si
H
Differences between 1st, 2nd and 3 rd row TMs
(1) Ionic Radii – 1st row small (Ti4+ 0.745 Å), 2nd and 3rd row larger but similar
to one another (Zr4+ = 0.860 Å, Hf4+ = 0.850 Å).
(2) Higher oxidation states more accessible down a group (d-orbitals further from
the nucleus) (MnO 4- = good oxidant, ReO 4- = poor oxidant).
(3) 1st row TMs have smaller ligand field splitting energies à High Spin
complexes possible, less likely to obey 18-electron rule.
(4) 1st row TMs exhibit more 1-electron redox processes (e.g. Fe II/III or CoI/II)
while 2-electron processes (RhI/III, Pt0/II/IV) dominate in 2nd row TM chemistry.
(5) 1st row TMs are less prone to M-M bonding.
(6) 1st row TM chemistry involves more paramagnetic complexes à
paramagnetic chemistry quite challenging (no NMR), so less well understood.
(7) Spin-orbit coupling much less significant for 1 st row TM complexes à allows
simple interpretation of UV-Vis spectra and magnetic moment measurements.
(8) Ligands less labile for 3rd row TM complexes compared with 2 nd row TM
complexes – 2nd row TM complexes often best for catalysis.
Electron Counting for simple molecules
Whenever you see a metal complex, work out:
(a) Metal oxidation state (organic chemistry knowledge will help assign the
correct charges to the ligands).
(b) dn Electron configuration (remember, all valence electrons are delectrons)
(c) Electron count for the complex
Chris Cummins (MIT)
Me3Si
I
OC
Ph 3P
Ir
PPh 3
OC
Cl
OC
(Vaska's compound)
Mn
Me 3Si
CO
CO
Br
Hg
Me
Me3C
SiMe3
Si
CMe 3
U
N CMe
3
N
N
CO
Ar
Ar
Ar
Ir+ = d 8
Cl- = 2
2 x PPh 3 = 2 x 2 = 4
CO = 2
Total = 16
Mn + = d 6
I- = 2
5 x CO = 5 x 2 = 10
Total = 18
Hg2+ = d10
Br- = 2
Me - = 2
Total = 14
U4+ = d/f2
3 x NR2- = 3 x 2 = 6
SiR3- = 2
Total = 10
Alternative methods for electron counting
Ph
OC
Ph3P
Ir
PPh3
Cl
Cl
K NC
Au
CN
PH recommends
this method
Method A
assign charge to metal
Method B
ligands and metal neutral
Ir 3+ = d6
2 x Cl- = 2 x 2 = 4
Ph- = 2
2 x PPh3 = 2 x 2 = 4
CO = 2
Total = 18
Ir = d9
2 x Cl = 2 x 1 = 2
Ph = 1
2 x PPh3 = 2 x 2 = 4
CO = 2
Total = 18
Au+ = d10
2 x CN- = 2 x 2 = 4
Total = 14
Au = 11 electrons
2 x CN = 2 x 1 = 2
1- charge = 1
Total = 14
IMPORTANT: whichever method
you use, be consistent !!!
Electron Counting Practice – Tougher Examples
Me2
Si
B
I
B
Rh
Rh
I
Rh
I
B
O
C
Ru
Rh
I
OC
Ru
C
O
CO
B
SiMe2(C 5H4)22- is just two Cpanions joined together
Borole = dianionic version of Cp
Q = How should the µ3-I ligands be counted ?
-
Q = How should the Ru-Ru
bond be counted ?
Q = how should the bridging
carbonyls be counted ?