Inorganic Chemistry 2 Chapter 4 - Yazd
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1 Reaction Mechanisms of d-Metal Complexes مپلکس هایکنش های کی واکانيسم ها م فلزاتd Inorganic Chemistry 2 Chapter 4 1 Alireza Gorji [email protected] Department of Chemistry, Yazd University [email protected] 2 [email protected] Content 1 2 3 4
Transcript of Inorganic Chemistry 2 Chapter 4 - Yazd
2/9/2015
1
Reaction Mechanisms of d-Metal
Complexes
مکانيسم های واکنش های کمپلکس های
dفلزات
Inorganic Chemistry 2
Chapter 4
1
Alireza [email protected]
Department of Chemistry, Yazd [email protected]
Content
1
2
3
4
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Time Scale
Thermodynamics Kinetics
G = H -T S G‡ = H‡ -T S‡
G° = -RTlnK G ‡ = -RTlnk
G
G
Reaction Coordinate
G‡
G
Reaction Coordinate
Large K → yield=100% Large k → fast reaction
Kinetics vs. Thermodynamics
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Thermodynamics Kinetics
A
G<0
G
B
A is unstable
ناپايدار
G>0
G
Reaction Coordinate
B
A
A is stable
پايدار
G‡ is small
GA is labile
واکنش پذير
A
B
A is inert
بی اثر
G‡ is large
G
Reaction Coordinate
A
B
A is unstable ناپايدار
A
G
Reaction Coordinate
labile
inert
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Thermodynamics Kinetics
G / H / S / K G‡ / H‡ / S‡ / k
Stable پايدار
Unstable ناپايدار
Inert بی اثر
Labile واکنش پذير
Spontaneousخودبخودی
nonspontaneous غيرخودبخودیFast سريع
Slow آهسته
Acid
Base
Electrophile
Nucleophile
Reaction Mechanisms
Intimate
Mechanism
Stoichiometry
Mechanism
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G
Reaction Coordinate
Stoichiometry Mechanism
Intimate
Mechanism
rds
1- Substitution Reaction
MLnX + Y MLnY + X
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Characteristic lifetimes for exchange of water molecules in aqua complexes
–Labile:
• s-block elements: Large e.g. Na+, K+, Ba2+ etc…
• d-block elements: 1st row, distorted geometries, d10
• f-block
– Inert:
• s-block elements (only a few are relatively ‘inert’); Small e.g. Be2+, Mg2+
• d-block elements: d3 and d6 in Oh high-field, e.g. CrIII, CoIII. Second and third row.
Lability & Inertness
Labile complexes Fast substitution reactions (< few min)
Inert complexes Slow substitution reactions (>h)
a kinetic concept
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L
M
L L
L
L
X
L
M
L L
L
L
X
L
M
L L
L
L
G
Ea
LFAE = LFSE(sq pyr) - LFSE(oct)
1- Substitution Reaction
MLnX + Y MLnY + X
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Stoichiometry Mechanisms
Stoichiometry Mechanisms in Substitution Reaction
Dissociative InterchangeAssociative
D IA
ML5X + YML5Y + X X=Leaving group
Y=Entering group
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D
Dissociative Mechanism in Substitution Reaction
ML5X ML5 + X slow
ML5 + Y ML5Y fast
rate = k1 [ML5X]
k1
k2
A
Associative Mechanism in Substitution Reaction
ML5X + Y ML5XY slow
ML5XY ML5Y + X fast
k1
k2
rate = k1 [ML5X][Y]
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Fast equilibrium
K1 = k1/k-1
k2 << k-1
For [Y] >> [ML5X]
Interchange Mechanism in Substitution Reaction
I
Intimate Mechanisms in Substitution Reaction
associative activation (a)
dissociative activation (d)
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Intimate Mechanisms in Substitution Reaction
d
a
Dd
Aa
Da
a
d
Ad
da
IdIa
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a d
A Aa Ad
D Da Dd
I Ia Id
Mechanisms in Substitution Reactions
Determination of Stoichiometry Mechanisms
1. Detection of intermediate by fast
spectroscopy and ultrafast spectroscopy.
2. Synthesis and isolation of intermediate.
3. Stereochemistry of reaction.
A & D
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Determination of Intimate Mechanisms
Experimental evidence a d
Sensitivity to entering group
Sensitivity to leaving group
trans effect
cis effect
Increasing of steric hindrance on cis ligands - +
Increasing of positive charge on complex + -
S‡ > 0
V‡ > 0
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Substitution reaction in square planar complexes
ML3X + Y ML3Y + X
M = Pt
Substitution of square planar Pt2+ complexes
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rate = k1 [S][PtA3X] + k2[Y][PtA3X]
rate = k1[PtA3X] + k2[Y][PtA3X]
rate = (k1 + k2[Y])[PtA3X]
If [Y] >> [PtA3X] rate = kobs[PtA3X]
kobs = (k1 + k2[Y])
solvent pathway
nucleophile
pathway
rate = k1 [S][PtA3X] + k2[Y][PtA3X]
rate = k1[PtA3X] + k2[Y][PtA3X]
rate = (k1 + k2[Y])[PtA3X]
If [Y] >> [PtA3X] rate = kobs[PtA3X]
kobs = (k1 + k2[Y])
slope = k2
k1
kobs
[Y]
k1 = solvent pathway
k2 = nucleophile pathway
rate law for square planar Pt2+ complexes
k2 nucleophile a
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[PtA2Cl2] + Y [PtA2ClY] + Cl
Y Donor atom
npt
Cl- Cl 3.04
C6H5SH S 4.15
CN- C 7.00
(C6H5)3P P 8.79
CH3OH O 0
I- I 5.42
NH3 N 3.06
The trans effect
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trans labilization
G
Reaction Coordinate
-acceptor-donor
Mechanism of the trans effect
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Selective synthesis using the trans effect
Cl
PtCl Cl
Cl
NH3 NH3
PtCl Cl
Cl
NH3
NH3
PtH3N NH3
NH3
NH3
PtH3N NH3
Cl
Cl- Cl
-
Cl-
Cl-
NH3
Cl
PtCl Cl
Cl
PPh3
PtCl Cl
Cl
PPh3 Py
Cl-
Cl-
Cl
PtCl Cl
Cl
PPh3Py
PtCl Cl
Cl
Py
Cl-
Cl-
NH3
PPh3
PtCl
Py
Cl
NH3Pt
Cl
H3N
Cl
NH3
PtCl NH3
Cl
PPh3PtCl
Py
Cl
2- -
2+ +
2- -
2- -
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ML5X + Y ML5Y + X
Substitution reaction in octahedral complexes
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The Eigen-Wilkins mechanism
ML5X + Y ⇌ ML5X‖Y fast
ML5X‖Y ⇀ ML5Y +X slowk
KE
rate = k[ML5X‖Y]
[ML5X‖Y]= KE[ML5X][Y]
rate = k KE[ML5X][Y]
if [Y]>>[ML5X] [Y]0 ≅ [Y][ML5X]0= [ML5X]+ [ML5X‖Y]= [ML5X](1+ KE[Y])
rate = k KE[ML5X]0[Y]/ (1+ KE[Y])
rate = k KE[ML5X]0[Y] 0/ (1+ KE[Y] 0)
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rate = k KE[ML5X]0[Y] 0/ (1+ KE[Y] 0)
k
Id
The Fuoss-Eigen equation
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Leaving group effects
Rate is independent of the nature of L
Entering group effects
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Rate is dependent on the nature of L
Entering group effects
Steric effects
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The effect of overall charge
[CoL5Cl]2+ + H2O [CoL5OH2]3+ + Cl- k1
[CoLL4Cl]+ + H2O [CoLL4OH2]2+ + Cl- k2
L = amine k1/ k2=1/1000
Activation Energetics
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Octahedral Substitution and ΔV‡
Octahedral Substitution General Rules
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Stereochemistry in Octahedral Substitution
The cis effect
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Base catalyzed hydrolysis of amines
Dissociative Conjugate Base (DCB) Mechanism
DCB
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Isomerization Reactions
Isomerization of chelates
1- Bond breaking
2- Twist
•Bailar Twist (C3)
•Ray-Dutt Twist (C3)
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Isomerization via bond breaking
Isomerization via Twist
Bailar Twist (C3)
Ray-Dutt Twist (C3)
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2- Redox reactions
Ox + Red ⇌ Red + Ox
Electron Transfer
Reaction
1- in electrochemical cell
2- in chemical reaction
Classification of Redox Mechanisms
• Non complementary electron transfer
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[Co(NH3)6]3+ + [Cr(OH2)6] 2+ [Co(OH2)6]2+ + [Cr(OH2)6] 3+ + 6NH3
Outer Sphere Electron Transfer OSET
L LI I
OSET: t2gt2g > t2geg > egeg
[FeIII(Phen)3]3+ + [FeII(CN)6]
4- [FeIII(Phen)3]2+ + [FeIII(CN)6]
3-
[FeIII(Phen)3]3+ + [CrII(OH2)6]
2+ [FeIII(Phen)3]2+ + [CrII(OH2)6]
3+
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• Characteristics: Electrons are transferred between the species (reductant
oxidant) without changes in their co-ordination spheres.
• Requirements: Redox reaction must be much faster than substitution
reactions.
– Slow substitution inert metal centers:
• d-block: d6 high-field e.g. high field Co3+, Fe2+; second and third
row d-elements (large CFSE).
– Ligands:
• Ideally, unable to bridge
• -acceptors
Outer Sphere Electron Transfer OSET
[FeIII(Phen)3]3+ + [FeII(CN)6]
4- [FeIII(Phen)3]2+ + [FeIII(CN)6]
3-
[Fe(CN)6]4- + [IrCl6]
2- [Fe(CN)6]3- + [IrCl6]
3-
[Co(NH3)5Cl]2+ + [Ru(NH3)6]2+ [Co(NH3)5Cl]+ + [Ru(NH3)6]
3+
Reactions ca. 100 times faster
than ligand exchange
(coordination spheres remain the same)
rate = k [A][B]
Ea
A B+
A B
A' B'+
G
"solvent cage"
Tunneling
mechanism
Outer Sphere Electron Transfer OSET
The metal ligand distances are different before and after electron transfer.
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OSET Mechanism
Rudy Marcus, 1992
Nobel Prize in Chemistry
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Reaction profile for OSET
[Fe(OH2)6]2++[Fe*(OH2)6]
3+[Fe(OH2)6]3+ +[Fe*(OH2)6]
2+
K = 3.0 M-1s-1 Ea = 32 kJ/mol
Exchange Reaction
G‡IS
G‡OS
G‡ET
Marcus Theory
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The Marcus equation
[Co(bipy)3]2++[Co(terpy)3]
3+ [Co(bipy)3]3++[Co(terpy)3]
2+ K=3.57
: (T=273 K)ثابت سرعت واکنش زير را حساب کنيد
[Co(bipy)3]2++[*Co(bipy)3]
3+ [Co(bipy)3]3++[*Co(bipy)3]
2+ k11=9.0 M-1s-1
[Co(terpy)3]2++[*Co(terpy)3]
3+ [Co(terpy)3]3++[*Co(terpy)3]
2+ k22=48.0 M-1s-1
k12=[(9.0 M-1s-1)(48.0 M-1s-1)(3.57)(1)]1/2
k12=39.0 M-1s-1
1- change of spin
2- change of symmetry
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را در شرايط زير حساب کنيدOSETثابت سرعت يک واکنش تک الکترونی
T=273 K, k11=9.0 M-1s-1, k22=48.0 M-1s-1, E= 1.0 v
ΔG=-n f E
ΔG=- (1)(96500)(1.0)= -96500
ΔG=-RT lnK
lnK = -96500/(8.314 273)
K = 2.91 1018
k12=[(9.0 M-1s-1)(48.0 M-1s-1)(2.91 1018 )(1)]1/2
k12=9.0 3.6 10 M-1s-1
Evidence for the Marcus equation
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Inner Sphere Electron Transfer ISET
ISET: t2gt2g < t2geg < egeg
• Inner-Sphere Mechanism Requires:
1. Labile metal complexes
2. Ligand capable of bridging
3. Ligand capable of receiving/delivering e-
Bridging ligands in ISET
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Reactions much faster
than outer sphere electron transfer
(bridging ligand often exchanged)
Ox-X + Red Ox-X-Redk1
k2
k3
k4
Ox(H2O)- + Red-X+
Ea
Ox-X Red+
Ox-X-Red
G
Ox(H2O)- + Red-X+
ISET mechanism
Rate = k[Ox-X][Red] k= (k1k3/k2 + k3)
ISET mechanism
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ISET and Linkage Isomerism
Summary
OSET: t2gt2g > t2geg > egeg
ISET: egeg > eg t2g > t2gt2g
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3- Oxidative Addition and Reductive Elimination
Oxidative Addition
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Oxidative Addition and Reductive Elimination
4-Photochemistry
Ground State A A* Excited Stateh
A +heat +luminescence Products
Photophysics Photochemistry
Quantum yield =
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Photochemistry
Photochemistry
Supramolecular photochemistry
Interamolecular photochemistry
Intermolecular photochemistry
A A* h
h
Ligand Field Transition
Charge Transfer Transition
Intervalence Transition
Intermetallic Transition
…..
Photochemistry
1- Ligand Field Transition
[Co(NH3)5Br]2++H2O [Co(NH3)5OH2]3++Br- Photosubstitution
2- Charge Transfer Transition
[Fe(C2O4)3]3- [Fe(OH2)6]
2++CO2 Photoredox
3- Intervalence Transition Photoredox
[R—MII—X—MIII—R] [R—MIII—X—MII—R] R+ + [MII—X—MII—R]
4- Interligand Transition
[Cr(acac)2(NH3) (N3)] N2 + …. Photoredox
5- Intermetallic transition
[ N2 + …. Photodissociationh
h
h
h
h
