Other Ligands—Chapter 6
P- donor ligands
Figure 6-13 Tolman’s Ligand Cone Angle
Organometallic Chemistry
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Organometallic Chemistry
How about stability??
Organometallic Chemistry
Decomposition pathway for ethyl groups: β- elimination
Alpha and gamma- elimination are less favored.
Organometallic Chemistry
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The M-H Bond Functionality:
Synthetic Routes
H
M- + H+
M
No change in M
oxidation state; This
is β-elimination
M• + H•
Oxidation state of M increases
by 1; can result from H2
addition to M2 dimers.
MH
Formal oxidation of M changes
oxidation state by 2; electron
withdrawing ligands stabilize
+
M
+
H
M oxidation state is
unchanged; electron donating
ligands stabilize
The M-H Bond Functionality: Reactivity
H
M- + H+
M
No change in M
oxidation state; reverse
is β-elimination
M• + H•
Oxidation state of M
reduced by 1; can yield H2
or initiate radical rxns
MH
Formal reduction of M
oxidation state by 2; electron
Withdrawing ligands stabilize
+
M
+
H
M oxidation state is
unchanged; electron donating
ligands stabilize
Acidity of MCO Hydrides
HM(CO)n + OH-
H2O + M(CO)n-
Ka
HCo(CO)4
~2
HCo(CO)3PPh3
1 × 10-7
HMn(CO)5
8 × 10-8
HRe(CO)5
very weak
H2Fe(CO)4
3 × 10-5 ; 1 × 10-14
CpCr(CO)3H
10-13.3
CpMo(CO)3H
10-13.9
CpW(CO)3H
10-16.1
Inorganic Chemistry Chapter 1: Table 22.6
© 2009 W.H. Freeman
Hydride Transfer Reactivity
HM(CO)n- + RX
XM(CO) +
RH
Rate = k2[HM-][RX]
Organometallics, 1984, 3, 646
Suppose one protonates the anionic
metal hydride of HW(CO)5- . Is it
possible that the resultant H2 would
remain bound to the metal?
Heinekey, JACS, 2005, 850-851;
Heinekey, JACS, 2006, 2615-2620
The η2-Dihydrogen as Ligand Story
Kubas, JACS, 1984, 10, 451.
Every Molecule Has a Story: The η2-H2 Complexes
H H
R3P
OC
W
C
O
CO
PR3
++
H H
P
P
Fe
C
N
H
H H
+
H
R3P
Ir
N
PR3
C
P
P
+ H+ - H+
H
R3P
HCO
W
PR3
C
O C
O
- stability towards H2 dissociation
- oxidative addition to dihydride
Kubas, LANL
+
H
P
P
Fe
P
P
C
N
H
- strong acid
- CNH ligand
Morris, U. Toronto
+
H H
R3P
H
Ir
PR3
N
C
- resonance forms
- H/D exchange
Crabtree, Yale
The η2-H2 Complexes
- Typically d6, Oh structures of Cr0, Mo0, W0, FeII, RuII, IrIII.
- Bonding: Delicate Balance Required for Stability
M
H
H
H
H
M
M
H
H
Morris, U. Toronto
σ - donor
Kubas, LANL
σ* acceptor
M2+(H-)2
- Examples of η2-H2 complexes
H H
CO
R3P
W0
PR3
OC
C
O
Kubas
++
H H
P
P
FeII
C
N
H
Morris
P
P
Crabtree, Yale
H H
+
Ph3P III H
Ir
N
PPh3
C
Crabtree
H2
IrIII
The η2- Dihydrogen as Ligand Story
Kubas, JACS, 1984, 10, 451.
Metal Carbonyl Anions: Nucleophilicity
{M}CO− + RX
RM(CO) + X−
Rate = k [MCO][RX]
Anion
CN
Anion
Product
CN
Relative
nucleophilicity
CpFe(CO)2̄
5
CpFe(CO)2R
6
7.0 x 106
CpRu(CO)2̄
5
CpRu(CO)2R
6
7.5 x 106
CpNi(CO)ˉ
4
CpNi(CO)R
5
5.5 x 106
Ru(CO)5̄
5
Ru(CO)5R
6
2.5 x 104
CpW(CO)3̄
6
CpW(CO)3R
7
~500
Mn(CO)5̄
5
Mn(CO)5R
6
77
CpMo(CO)3̄
6
CpMo(CO)3R
7
67
CpCr(CO)3̄
6
CpCr(CO)3R
7
4
Co(CO)4̄
4
RCo(CO)4
5
1
V(CO)6-
6
RV(CO)6
7
<< 1
Fe(CO)42-
4
RFe(CO)4-
5
>> 7.0 x 106
Another electron rich metal center: Also reacts with
Organic Electrophiles: Vaska’s Complex
Illustration from page 140
Organometallic Chemistry
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Synthesis of Fischer Carbene
Organometallic Chemistry
Organometallic Chemistry
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Figure 6- 5 Bonding in Carbyne Complexes
Organometallic Chemistry
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Schrock vs. Fischer Carbene
Organometallic Chemistry
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Fischer vs. Schrock Carbene
Schrock gets an idea:
Other Organic Ligands
Illustration from page 150
Organometallic Chemistry
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Inorganic Chemistry Chapter 1: Figure 22.17
© 2009 W.H. Freeman
Acidity of MCO Hydrides
HM(CO)n + OH-
H2O + M(CO)n-
Ka
HCo(CO)4
~2
HCo(CO)3PPh3
1 × 10-7
HMn(CO)5
8 × 10-8
HRe(CO)5
very weak
H2Fe(CO)4
3 × 10-5 ; 1 × 10-14
CpCr(CO)3H
10-13.3
CpMo(CO)3H
10-13.9
CpW(CO)3H
10-16.1
The η2-Dihydrogen as Ligand Story
Kubas, JACS, 1984, 10, 451.
The η2-H2 Complexes
- Typically d6, Oh structures of Cr0, Mo0, W0, FeII, RuII, IrIII.
- Bonding: Delicate Balance Required for Stability
M
H
H
H
σ - donor
H
M
M
H
H
σ* acceptor
M2+(H-)2
- Examples of η2-H2 complexes
H H
CO
R3P
W0
PR3
OC
C
O
Kubas
++
H H
P
P
FeII
C
N
H
Morris
P
P
H H
+
Ph3P III H
Ir
N
PPh3
C
Crabtree
Every Molecule Has a Story: The η2-H2 Complexes
H H
R3P
OC
W
C
O
CO
PR3
++
H H
P
P
Fe
C
N
H
H H
+
H
R3P
Ir
N
PR3
C
P
P
+ H+ - H+
H
R3P
HCO
W
PR3
C
O C
O
- stability towards H2 dissociation
- oxidative addition to dihydride
Kubas
+
H
P
P
Fe
P
P
C
N
H
+
H H
R3P
H
Ir
PR3
N
C
- strong acid
- CNH ligand
- resonance forms
- H/D exchange
Morris
Crabtree