The CBC Method of electron counting

Report
Five slides about…
Consider…
The ‘ionic’ method says
2 Cp6e- each
 2 Me2e- each
 Ligand total 16e
(-1 each)
(-1 each)
-4
So Ti+4 (d0) since it is neutral
 16e- exception?
 Problem…is this really a +4 metal interacting
with four anions?

The ‘covalent’ method says
2 Cp
5e- each
 2 Me
1e- each
 Ligand total 12e
So Ti0 (d4) since it is neutral
 16e- exception?
 Problem…assuming the d-electrons are nonbonding how is this diamagnetic?

CBC ligand classification

L
 Ligand donates two electrons
 CO, phosphines, alkenes

X
 Ligand donates one electron
 H, halides, alkyl

Z
 Ligand donates zero electrons
 boranes
How to count? [MLlXxZz]

Total electron count
 From ligands: 2l + x
 From metal: m
 m + 2l + x

Valence number (VN) for the metal = x + 2z

Ligand bond number (LBN) for the metal = l + x + z

dn count for metal = m - VN
Current example
X
H3C•
L
L2X
X
Counting
Metal is classified as ML4X4
 Electron count: 4 + 10 + 2 = 16
 VN: 4
 LBN: 8
 dn: 0

What have we learned?
Electrons: 16
 VN: 4
 Classification: ML4X4

Ti
0
Electron Count
8
ML2
Valence
1
2
10
MLX2
12
13
ML4
ML3X
ML2X2
MLX3
MX4
6%
11
ML3
ML2X
3
4
9
ML4X
ML2X3
<1%
http://www.columbia.edu/cu/chemistry/groups/parkin/mlxz.htm
16
ML4X2
1%
18
ML7
1%
ML6X
<1%
ML5X2
1%
ML4X3
5%
ML3X4
6%
17
ML6
2%
ML5X
ML3X3
<1%
ML2X4
7%
15
ML5
ML3X2
MLX4
1%
14
ML6X2
4%
ML5X3
9%
ML4X4
49%
ML5X4
4%
A different view
60
Ti
50
%
40
30
20
10
0
6
7
8
9
10 11 12 13 14 15 16 17 18
Electron Count
http://www.columbia.edu/cu/chemistry/groups/parkin/mlxz.htm
What about valence?
VN: 4 is not saying it is +4
 Gives the d0 count

16
14
Ti
12
%
10
8
6
4
2
0
0
http://www.columbia.edu/cu/chemistry/groups/parkin/mlxz.htm
1
2
Valence Number
3
4
What is LBN?
Not coordination number
 Number of sites on the metal
 LBN: 8 while CN: 12

70
Ti
60
50
%
40
30
20
10
0
2
3
http://www.columbia.edu/cu/chemistry/groups/parkin/mlxz.htm
4
5
6
7
Ligand Bond Number
8
9
Further readings

M.L.H. Green J. Organomet. Chem. 1995,
500, 127-148.

G. Parkin, in Comprehensive
Organometallic Chemistry III, Volume 1,
Chapter 1; R.H. Crabtree and D.M.P.
Mingos (Eds), Elsevier, Oxford, 2006.

http://www.columbia.edu/cu/chemistry/grou
ps/parkin/cbc.htm

similar documents