aerobic catalytic oxidative radical reactions radical reactions
TRANSCRIPT
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Aerobic Catalytic Oxidative
Radical Reactions
Lit. seminar
Radical Reactions
Y. Tanaka (D2)
10. 5. 19
Use of Molecular Oxygen in Catalytic Cycle
Cat. ox. Cat. red.
Substrate Product
Cat. ox. Cat. red.
Substrate Product
OxidantByproduct
Oxidant ideal: O2
real: DDQ, CAN, etc…
Catalytic one electrondonor/acceptor
O2 H2O
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Contents
1. Cu-TEMPO catalyst system
2. Organic photo catalyst system
1. Cu-TEMPO catalyzed Aerobic Oxidation of Alcohols
1. Cu-TEMPO catalyst system
2. Organic photo catalyst system
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Cu-TEMPO catalyzed Aerobic Oxidation of Alcohols
CuCl (10 mol %), TEMPO (10 mol %)
DMF, 25 ℃R-OH
R
O
H
Semmelhack et al. J. Am. Chem. Soc. 1984, 106, 3376.
Proposed Reaction Mechanism by Semmelhack
Actual oxidant
Semmelhack et al. J. Am. Chem. Soc. 1984, 106, 3376.
O2 : Oxidize Cu(1)
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Proposed Reaction Mechanism by Sheldon
Actual oxidant
Sheldon et al. Org. Biomol. Chem. 2003, 1, 3232.
O2 : Oxidize TEMPOH
Verification of the Mechanism 1
Cu(1) + TEMPO
Cu(1) + TEMPO
Cu(2) + TEMPOH
N2, rt, 24 h
Cu(1) + TEMPO
Cu(2)
Cu(1)
TEMPO
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Verification of the Mechanism 2
Instantaneously occur in basic H2O (checked by the color)
Verification of the Mechanism 3
Kinetic isotope effect
KIE
Hammet
Compared with
other reactions
Kinetic isotope effect
D
OH
HCu-TEMPO
H
O
D
O+
catalytic under O2: kH/kD = 5.42
Stoichio. under N2: kH/kD = 5.77
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Verification of the Mechanism 3
Hammett plotHammett plot
Verification of the Mechanism 3
R.D.S.
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Verification of the Mechanism 3
cf. Galactose oxidase
Proposed Hydrogen Abstraction Mechanism
By analogy with galactose oxidase
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Proposed Catalytic Cycle
Further Improvement through Condition Optimization
Sheldon et al. Chem. Comm. 2003, 2414.
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Other Examples of Cu-TEMPO Catalyzed Reactions
Vatele SYNLETT 2009, 13, 2143.
Jiao et al. J. Am. Chem. Soc. 2010, 132, 28.
Vatele SYNLETT 2009, 13, 2143.
[Cat] = CuBr2
T = 60 ℃
2. Organic Photo Catalyst System
1. Cu-TEMPO catalyst system
2. Organic photo catalyst system
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Aerobic Photocatalytic Reactions
Floreancig et al.
Fukuzumi et al.
Fukuzumi et al.
Aerobic Oxidation of Toluene with Photo Catalyst
ConditionsConditions
33 mol %
O2, CHCl3, 25℃
Fukuzumi et al. J. Am. Chem. Soc. 2003, 125, 12850.
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Proposed Catalytic Cycle
Photo catalyst
HOMO
LUMO
HOMO
LUMO
HOMO
LUMO
Organic Photo Catalysts
1
2
3 4
5 6
7 8 10
11
9
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Organic Photo Catalysts
One electron reduction potential of ground state
HOMO
LUMO
HOMO
LUMOe−−−−
cf. O2 + e−−−− O2 : −−−−0.72 eV
Organic Photo Catalysts
One electron reduction potential of singlet exited state
HOMO
LUMO
HOMO
LUMOe−−−−
cf. DDQ: +0.56 V
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Organic Photo Catalysts
Fluorescence life time
Fluorescence
Organic Photo Catalysts
Singlet exited energy E0red−E0
red*
Nearly HOMO-LUMO gap
1: 3.81 eV
λmax = 312 nm
8: 3.58 eV 10: 2.75 eV
λmax = 417nm
1 eV = ca. 1200/λ (nm-1) = 23 kcal/mol
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Organic Photo Catalysts
Quenching rate constants
Fluorescence
E0red vs Reactivity
1 3 4
5 6
10
11
0.1 eV difference: ca. 50 times faster reaction 27 89
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Reaction with p-tolunitrile
E0red* = +3.17 V
33 mol %rt
Mercury lamp through
acetophenone –methanol filter
(>300 nm)
254, 365, 405, 436, 546, 577, 579 nm
Reaction with Xylens
33 mol %rt
Xenon lamp through UV cutoff filter (> 310 nm)
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Aerobic Photocatalytic Reactions
Floreancig et al.
Fukuzumi et al.
Fukuzumi et al.
Stichio. Reaction
( )n( )n Stichio.
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Proposed Reaction Mechanism
Floreancig et al. J. Am. Chem. Soc. 2001, 123, 3842.
Catalytic Reaction
Catalytic
Floreancig et al. Org. Lett. 2001, 3, 4123.
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Condition Optimization
NMQ+
Substrate Scope
NMQ+
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Other Examples of This Type Reaction
Floreancig et al. Org. Lett. 2002, 4, 3443.