Transcript Oxidative addition, reductive elimination Heck reaction, Suzuki coupling Concerted addition

Oxidative addition,
reductive elimination
Heck reaction, Suzuki coupling
Concerted addition
LnM
+ X Y
LnM
X
Y
X
LnM
Y
Often with H2, alkanes, R3SiH, O2
Stepwise
X
LnM + X Y
LnM X Y
LnM
Y
Often with HX, R3SnX, alkyl acyl and allyl halides
and an electron-rich metal (IrI, RhI, Pd(0))
5/23/2016
Oxidative Addition, Reductive Elimination
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Oxidative addition,
reductive elimination
Sometimes radical mechanism:
RIrCl(CO)L2X
Test:
RX
• Formation R-R
• CIDNP
• Br
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R
IrCl(CO)L2
RIrCl(CO)L2
M
Oxidative Addition, Reductive Elimination
2
Oxidative addition,
reductive elimination
Promote oxidative addition:
• Strongly basic metal fragment
• Concerted: weak, apolar s bond
• Stepwise: polar bond,
good leaving group
• C-H: arene > alkane
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Oxidative Addition, Reductive Elimination
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The Heck reaction
"Pd"
ArX +
Ar
R
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Oxidative Addition, Reductive Elimination
+ HX
R
4
The Heck reaction
H+
Ar
R
H
Pd
ArX
Pd
ox add
+
Ar
Ar
Pd
X
subst
+
R
-elim
Ar
+
Pd
X-
ins
Pd
R
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R
Ar
R
Oxidative Addition, Reductive Elimination
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Suzuki and Stille coupling
RX + ArB(OH)2
RX + ArSnR'3
"Pd"
"Pd"
RAr + XB(OH)2
RAr + XSnR'3
R = aryl or vinyl
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Oxidative Addition, Reductive Elimination
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Suzuki and Stille coupling
RX
Pd
RAr
ox add
red elim
R
R
Pd
Pd
Ar
X
subst
EX
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ArE
Oxidative Addition, Reductive Elimination
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Reductive elimination
Usually easy for:
• H + alkyl / aryl / acyl
• alkyl + acyl
• SiR3 + alkyl etc
Often slow for:
• alkoxide + alkyl
• halide + alkyl
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Oxidative Addition, Reductive Elimination
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Hydrogenation (1)
H
H
M
H
coord
red elim
H
H
M
H
M
H
ins
ox add
H2
M
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H
Variation:
direct s-bond metathesis
of M-R with H2
Oxidative Addition, Reductive Elimination
9
Hydrogenation (2)
M
H2
ox add
coord
M
M
H
H
ins
red elim
H
H
M
H
5/23/2016
(what is wrong
with this cycle?)
H
Oxidative Addition, Reductive Elimination
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