Main-group Elements (Bi) in Catalysis for Organic Synthesis
Xiaheng ZhangMacMillan Group Meeting
March 18th 2020
XR
LX
R
L
Mechanisms of Activation Mode for Main-group Elements
■ Activation mode of transition metal elements
XR
LX
R
L
M
! donation into empty d-orbital
M
" donation from d-orbital into "∗-orbital
! donation into empty p-orbital " donation from p-orbital into "∗-orbital
■ Activation mode of main-group elements
Activation of Small Molecules by Main-group Elements
Frustrated Lewis pairs activation
Stephan, D. W. et al. Science 2006, 314, 1124.
Activation of H2 by carbenes
iPr2N
Mes2P B
F4
H2 25 oC
> 100 oCMes2P B
F4
H H
Stephan, D. W. et al. Science 2016, 354, aaf7229.
Me
MeMe H2 35
oCiPr2N
Me
MeMe
Frey, G. D.; Lavallo, V.; Donnadieu, B.; Schoeller, W. W.; Bertrand, G. Science 2007, 316, 439.
H H
Catalysis Enabled by Main-group Elements
Frustrated Lewis pairs catalyzed hydrogenation
Chernichenko,K.;Madaraśz,A.;Paṕai,I.;Nieger,M.;Leskela,̈ M.;Repo,T. Nat. Chem. 2013, 5, 718.
FLP catalyzed C-H activation
H2 FLP (5 mol%)
Leǵare,́M.-A.;Courtemanche,M.-A.;Rochette,É.;Fontaine,F.-G. Science 2015, 349, 513.
BuPh
Bu
Ph
H
H
N
B(C6F5)2
Me
Me
FLP (Cat.)
N
Me
HN
Me
BpinH-Bpin FLP (2.5 mol%)N
BH2
R
R
FLP (Cat.)
Catalysis Enabled by Main-group Elements
C-H silylation catalyzed by alkali metal catalyst
Toutov, A. A.; Liu, W.-B.; Betz, K. N.; Fedorov, A.; Stoltz, B. M.; Grubbs, R. H. Nature 2015, 518, 80.
Imine hydrogenation catalyzed by alkaline earth metal catalyst
KOt-Bu (20 mol%)
Harder, S. et. al. Nat. Catal. 2018, 1, 40.
H2 Ca (10 mol%)
N
Me
H
Et3SiHN
Me
SiEt3
MeMe
NMe
MeMe
NMe
H
H
Main-group Elements (Bi) in Catalysis for Organic Synthesis
■ The facts of bismuth
■ Synthesis of organobismuthines
■ The application of organobismuthines in organic synthesis
■ Redox chemistry of bismuth
Outline
Why do people care about bismuth catalysis
Bi
Peptobismol OTC
stomach disorders
■ naturally abundant
■ ‘green element’ even less toxic than NaCl■ widely used in industry, antibiotics, radiopaque bone cements, polymers
electron configuration: 4f145d106s26p3
common oxidation state: +1, +3, +5
Can we discover new reactivity that is unique to bismuth catalysis?
Main-group Elements (Bi) in Catalysis for Organic Synthesis
■ The facts of bismuth
■ Synthesis of organobismuthines
■ The application of organobismuthines in organic synthesis
■ Redox chemistry of bismuth
Outline
Synthesis of organobismuthines
■ Synthesis of trivalent organobismuthines
BiCl3ArMgBr, ArLi or ArBr, CoBr2, Zn
BiAr3
BiCl3 (0.5 eq)BiAr2Cl
BiCl3 (2.0 eq)BiArCl2
■ Synthesis of highly functionalized trivalent organobismuthines
Gagnon, A. et. al. J. Org. Chem. 2016, 81, 5401.
Bi
OH
3
NaBH4 Bi
OH
3
97% yield
BrCH2CO2EtPPh3Bi 3
CO2Et
80% yield
Bi3
Me
99% yield
HO
MeMgBr Bi 3
82% yield
Ph3PCH3It-BuOK
Synthesis of organobismuthines
■ Synthesis of pentavalent organobismuthines
Michaelis, A. Ber. Dtsch. Chem. Ges. 1887, 20, 52.Barton, D. H. R.; Finet, J.-P. Pure Appl. Chem. 1987, 59, 937.
Bi3
Br2
Cl2 or PhICl2
Bi3
Cl
Cl
NaF or AgFBi
3
F
F
K2CO3O3CBi3
RCO2H, H2O2Bi
ROCO
ROCO 5Bi
3
Br
Br
Main-group Elements (Bi) in Catalysis for Organic Synthesis
■ The facts of bismuth
■ Synthesis of organobismuthines
■ The application of organobismuthines in organic synthesis
■ Redox chemistry of bismuth
Outline
Organobismuth as arylation reagents
■ The first arylation reaction using organobismuthines
75% yield
N
MeO
HO NPh3BiCO3
DCMN
MeO
ON
N
MeO
ON
Ph
Barton, D. H. R.; Lester, D. J.; Motherwell, W. B.; Papoula, M. T. B. J. Chem. Soc., Chem. Commun. 1980, 246.
■ The first C-arylation of phenols organobismuthines
OH Ph3BiCO3
TMG
OH
Ph
76% yield
Organobismuth as arylation reagents
■ O-arylation and C-arylation controlled by condition
90% yield 90% yield
91% yield 57% yield
Me
Me
O
Me
BiPh3X
Me
Me
O
Me
Ph
Me
Me
O
MePh
Ph4BiO2CCF3
TMG
basic conditions
Ph4BiO2CCF3
Cl3CCO2H
acidic or neutral conditions
OH
PhOPh
O
PhCO2Et
OPh
CO2Et
Me
Me
OPhMe
Me
OPh
72% yield 58% yield
Barton, D. H. R. et. al. J. Chem. Soc., Chem. Commun. 1980, 827. Barton, D. H. R. et. al. J. Chem. Soc., Chem. Commun. 1981, 503.
Organobismuth as arylation reagents
■ O-arylation of alcohols, diols, aminoalcohols
73% yield
Me
MeOH Ph4BiO2CCF3 or Ph3Bi(OAc)2
DCM or toluene
David, S.; Thieffry, A. J. Org. Chem. 1983, 48, 441. Barton, D. H. R. et. al. J. Chem. Soc., Chem. Commun. 1986, 65.
Me
MeO
Ph
tBu
OPh
OH
OPh
OHMe
88% yield
PhHNOH
51% yield
HO OPhMe Me
99% yield
MeOOPh
86% yield
PhPh
O
OPh
88% yield
HOOPh
80% yield
Organobismuth as arylation reagents
■ O-arylation of tertiary alcohols via Cu catalysis
OH
Me
Me Ph3Bi(OAc)2, Cu(OAc)2, Cy2NMe, O2
DCM or toluene
Ikegai, K.; Fukumoto, K.; Mukaiyama, T. Chem. Lett. 2006, 35, 612. Mukaiyama, T.; Sakurai, N.; Ikegai, K. Chem. Lett. 2006, 35, 1140.
89% yield
EtO2C
O
Me
Me
EtO2CPh
O
Me
Me
EtO2CPh
89% yield
OMe
EtO2CPh
Ph
94% yield
O
Me
EtPh
88% yield
OPh
BnN
Ph
87% yield
O
Me
Me
MePh
50% yield
O
Me
MePhTBSO
O
N
Organobismuth as arylation reagents
■ Cu catalyzed arylation of N, S-nucleophiles
Nu
Me
Me Ph3Bi(OAc)2 or Ar3Bi, Cu(OAc)2, O2
Gagnon, A. et. al. Synthesis 2017, 49, 1707.
96% yield
Nu
Me
MePh
HN
Ph
80% yield 91% yield
Me
Me
HN
OBn
Ph
Ph
O
O NH
HN
O
PhtBu
N
MeO2C
Ph-pMe
87% yield
N
N
Ph
87% yield
N N
N
Ph
60% yield
N NN
N
Ph
87% yield
Ph
S
Ph
84% yield
MeO
Organobismuth as arylation reagents
■ Cu catalyzed arylation of N, S-nucleophiles
Nu
Me
Me Ph3Bi(OAc)2 or Ar3Bi, Cu(OAc)2, O2
Gagnon, A. et. al. Synthesis 2017, 49, 1707.
96% yield
Nu
Me
MePh
HN
Ph
80% yield 91% yield
Me
Me
HN
OBn
Ph
Ph
O
O NH
HN
O
PhtBu
N
MeO2C
Ph-pMe
87% yield
N
N
Ph
87% yield
N N
N
Ph
60% yield
N NN
N
Ph
87% yield
Ph
O
NMe
52% yield
Me3Bi
Cross-coupling using organobismuth
Pd
Rh
CO2EtPh3Bi
CO2EtPh
Pd
Ph3BiN
N Cl
FGN
N Ph
FG
Pd
Ph3BiPO
Ph
EtOH P
OPh
EtOPh
Pd
c-Pr3BiN Cl
CN
N
CN
Gagnon, A.; Duplessis, M.; Alsabeh, P.; Barabé, F. J. Org. Chem. 2008, 73, 3604.
Wang, T.; Sang, S.; Liu, L.; Qiao, H.; Gao, Y.; Zhao, Y. J. Org. Chem. 2014, 79, 608.Kawamura, T.; Kikukawa, K.; Takagi, M.; Matsuda, T. Bull. Chem. Soc. Jpn. 1977, 50, 2021.
Gagnon, A. J. Org. Chem. 2016, 81, 5401.
O
Ph3Bi
O
Ph
Li, C.-J. et. al J. Am. Chem. Soc. 2001, 123, 7451.
OPh3BiCl2, PBu3
OPh
Krische, M. J. J. Am. Chem. Soc. 2004, 126, 5350.
Bi redox chemistry is unclear with rare examples
Main-group Elements (Bi) in Catalysis for Organic Synthesis
■ The facts of bismuth
■ Synthesis of organobismuthines
■ The application of organobismuthines in organic synthesis
■ Redox chemistry of bismuth
Outline
Bi(III)/Bi(V) redox activation
Jurrat, M.;Maggi, L.;Paṕai,I.;Lewis, W.;Ball, L. T. Nat. Chem. 2020, 12, 260.
SO O
Bi X B(OH)2 SO O
Bi OH
[O]OH
ortho-Arylation of phenols via Bi(III)/Bi(V) redox activation
OH
HO
iPr
Me
Liganasantibacterial, cyctotoxic
OH
CO2H
NH
N
NN
OAr
Pharmaceuticalsaplastic anemia
N
N
OH
Cl
Agrochemicalsherbicide
Bi(III)/Bi(V) redox activation
■ Current approaches for the preparation of 2-hydroxybiaryls
Jurrat, M.;Maggi, L.;Paṕai,I.;Lewis, W.;Ball, L. T. Nat. Chem. 2020, 12, 260.
H
OH
R
H
O
R
H, X, Li
PG, DG
H, X, Li OR
OH
R
2-hydroxybiaryls
OBiPh3XPh4BiO2CCF3
TMG
basic conditions
Ph4BiO2CCF3
Cl3CCO2H
acidic or neutral conditions
OH
Ph
OPh
■ Barton’s pioneer discovery
■ O or C arylation is highly dependent on the nature of the organobismuth and reaction conditions■ multistep synthesis of arylbismuth reagents, transfer one of the aryl groups in the organobismuth■ lack of systematic studies of mechanism which impedes practical exploration of the method
Bi(III)/Bi(V) redox activation
Jurrat, M.;Maggi, L.;Paṕai,I.;Lewis, W.;Ball, L. T. Nat. Chem. 2020, 12, 260.
SO O
Bi X B(OH)2 SO O
Bi OH
[O]OH
ortho-Arylation of phenols via Bi(III)/Bi(V) redox activation
■ one-pot boron-to-bismuth transmetallation ■ commercially available starting materials■ completely prevents the formation of O-arylated products■ operates under air in non-anhydrous conditions
Bi(III)/Bi(V) redox activation for ortho-Arylation of phenols
Jurrat, M.;Maggi, L.;Paṕai,I.;Lewis, W.;Ball, L. T. Nat. Chem. 2020, 12, 260.
■ Reaction design
SO O
Bi X
SO O
Bi
B(OH)2
B-to-Bi transmetallation
mCPBA
Bi(III) to Bi(V) oxidationBi
OOH
SO
O
O
Cl
OH
phenol deprotonation
Bi
OO
SO
O
O
Cl
HO
arylated product
exocyclicaryl group
Bi(III)/Bi(V) redox activation for ortho-Arylation of phenols
Jurrat, M.;Maggi, L.;Paṕai,I.;Lewis, W.;Ball, L. T. Nat. Chem. 2020, 12, 260.
SO O
Bi OTs SO O
Bi
B-to-Bi transmetallation
B(OH)2
(1.1 equiv.)
K2CO3 (1.2 equiv.)
PhMe/water (99/1), 60 oC, 2h
SO O
Bi F
SO OLi Li
SO OnBuLi
ArBiBr2BiBr3 Ar3Bi
■ Transmetallation to universal bismacyclic precursor
TsOH
Bi(III)/Bi(V) redox activation for ortho-Arylation of phenols
Jurrat, M.;Maggi, L.;Paṕai,I.;Lewis, W.;Ball, L. T. Nat. Chem. 2020, 12, 260.
SO O
Bi OTs SO O
Bi
B(OH)2
(1.1 equiv.)
K2CO3 (1.2 equiv.)
PhMe/water (99/1), 60 oC, 2h
■ Transmetallation to universal bismacyclic precursor
>99% yield
SO O
Bi NMe2
>99% yield
SO O
Bi CN
>99% yield
SO O
Bi
F3CO
>99% yield
SO O
Bi
Me
Me
Me
>99% yield
SO O
Bi
>99% yield
SO
BiNBoc
>99% yield
SO
Bi
>99% yield
SO
BiN
O
Me
MeN
OMe
NH
Bi(III)/Bi(V) redox activation for ortho-Arylation of phenols
Jurrat, M.;Maggi, L.;Paṕai,I.;Lewis, W.;Ball, L. T. Nat. Chem. 2020, 12, 260.
SO O
Bi OTs SO O
Bi
B(OH)2
(1.1 equiv.)
K2CO3 (1.2 equiv.)
■ One-pot, Bi(V)-mediated arylation of phenols and naphthols
69% yield
OH
OH
mCPBA, r.t., 10 min
OH
77% yield
OHMeO
OMe
F
59% yield
OH
F
Br
OH
Me
Me Me
89% yield
OH
87% yield
Br
OH
59% yield
OHN
93% yield
p-F
OH
90% yield
p-F
HN
N
SMe
Bi(III)/Bi(V) redox activation for ortho-Arylation of phenols
Jurrat, M.;Maggi, L.;Paṕai,I.;Lewis, W.;Ball, L. T. Nat. Chem. 2020, 12, 260.
SO O
Bi OTs SO O
Bi
B(OH)2
(1.1 equiv.)
K2CO3 (1.2 equiv.)
■ One-pot, Bi(V)-mediated arylation of phenols and naphthols
OH
OH
mCPBA, r.t., 10 min
+
SO O
Bi OmCBAcOH elution
SO O
Bi OAc
B(OH)2
96%
Bi(III)/Bi(V) redox activation for ortho-Arylation of phenols
Jurrat, M.;Maggi, L.;Paṕai,I.;Lewis, W.;Ball, L. T. Nat. Chem. 2020, 12, 260.
SO O
Bi OTs SO O
Bi
B(OH)2
(1.1 equiv.)
K2CO3 (1.2 equiv.), 1h
■ Mechanistic studies for the reaction
FF
SO O
Bi OH H2OS
O OBi O
S
O
O
Bi
>99%
K2CO3,PhMe/water
30 minr.t., 99%
B(OH)2
F
isolated
plausible pre-transmetallation intermediate
Bi(III)/Bi(V) redox activation for ortho-Arylation of phenols
Jurrat, M.;Maggi, L.;Paṕai,I.;Lewis, W.;Ball, L. T. Nat. Chem. 2020, 12, 260.
■ Reaction design
SO O
Bi X
SO O
Bi
B(OH)2
B-to-Bi transmetallation
mCPBA
Bi(III) to Bi(V) oxidationBi
OOH
SO
O
O
Cl
OH
phenol deprotonation
Bi
OO
SO
O
O
Cl
HO
arylated product
exocyclicaryl group
Bi(III)/Bi(V) redox activation for ortho-Arylation of phenols
Jurrat, M.;Maggi, L.;Paṕai,I.;Lewis, W.;Ball, L. T. Nat. Chem. 2020, 12, 260.
SO O
Bi
■ Mechanistic studies for the reaction
F1) mCPBA, PhMe2) DBU
Bi
OO
SO
O
Bi
SO
O
F
F
(X-ray)
Bi(V) dimer
Bi(V) dimermCPBA
Bi
OmCBOH
SO
O
mCPBA
Bi
OmCBOmCB
SO
O
mCBA/Bi = 1.3 2NMR ratio
HO
F
PhOHPhOH
Bi(III)/Bi(V) redox activation for ortho-Arylation of phenols
Jurrat, M.;Maggi, L.;Paṕai,I.;Lewis, W.;Ball, L. T. Nat. Chem. 2020, 12, 260.
SO O
Bi
■ Mechanistic studies for the reaction
F1) mCPBA, PhMe2) DBU
Bi
OO
SO
O
Bi
SO
O
F
F
(X-ray)
Bi(V) dimer
Bi(V) dimermCPBA
Bi
OmCBOH
SO
O
mCPBA
Bi
OmCBOmCB
SO
O
mCBA/Bi = 1.3 2NMR ratio
HOPhOH
Fk > 40 M-1S-1
PhOH
Bi(III)/Bi(V) redox activation for ortho-Arylation of phenols
Jurrat, M.;Maggi, L.;Paṕai,I.;Lewis, W.;Ball, L. T. Nat. Chem. 2020, 12, 260.
SO O
Bi
■ Mechanistic studies for the reaction
F
d0-PhOH (5.0 eq)d5-PhOH (5.0 eq)
OH
F
mCPBA, PhMe, r.t.
kH/kD = 1.03
SO O
Bi F
OH
F
mCPBA, PhMe, r.t.
kH/kD = 0.83
OH
D
H
Bi(III)/Bi(V) redox activation for ortho-Arylation of phenols
Jurrat, M.;Maggi, L.;Paṕai,I.;Lewis, W.;Ball, L. T. Nat. Chem. 2020, 12, 260.
SO O
Bi
■ Mechanistic studies for the reaction
F
Bi
OmCBOH
SO
O
Bi
OmCBO
SO
O
FF
k > 40 M-1S-1k > 1.6 M-1S-1RDS
PhOH
-H2O
OH
F
PhOH, mCPBA
PhMe, r.t.
mCPBA
What about Bi(III)/Bi(V) redox catalysis?
Planas, O.; Wang, F.; Leutzsch, M.; Cornella, J. Science. 2020, 367, 313.
■ Fluorination of arylboron via Bi(III)/Bi(V) redox catalysis
Bpin F
Bi
SON
F3C
BF4
Bi(III) (10 mol%)NaF (5.0 eq), CDCl3, 90 oC
NCl Cl
F
BF4 (1.0 eq)
90% yield
F
TMS
71% yield
F
Ph
77% yield
F
Me
55% yield
FMeO
36% yield
FCl
84% yield
FMe
Me
Br
45% yield
F
Me
F
49% yield
Fluorination of arylboron via Bi(III)/Bi(V) redox catalysis
Planas, O.; Wang, F.; Leutzsch, M.; Cornella, J. Science. 2020, 367, 313.
■ Proposed mechanism for Bi(III)/Bi(V) redox catalysis
BY2F
Bi
SON
F3C
X
C-F bond formation
Bi
SON
F3C
F-X
OA
Bi
SON
F3C
PhF
X
RETM
electrophile
Fluorination of arylboron via Bi(III)/Bi(V) redox catalysis
Planas, O.; Wang, F.; Leutzsch, M.; Cornella, J. Science. 2020, 367, 313.
■ Proof of concept study
Bi
SOO
Me
XeF2 (1.0 eq)
CHCl3, 0 oC
>95% isolated
Bi
SO
O
Me
F F
FBi
SOO
Me
F
X-ray
Bi
SOO
F
Me
F110 oCCDCl3
45% yieldreductive elimination
from Bi(V) center
Fluorination of arylboron via Bi(III)/Bi(V) redox catalysis
Planas, O.; Wang, F.; Leutzsch, M.; Cornella, J. Science. 2020, 367, 313.
■ Ligand effect for the reductive elimination
Bi
SOO
Me
XeF2 (1.0 eq)
F
45% yield
then 110 oC
Bi
SON
F3C
Bi
SON
Me
XeF2 (1.0 eq)
F
28% yield
then 110 oC
XeF2 (1.0 eq)
F
94% yield
then 110 oC
Fluorination of arylboron via Bi(III)/Bi(V) redox catalysis
Planas, O.; Wang, F.; Leutzsch, M.; Cornella, J. Science. 2020, 367, 313.
■ Kinetic analysis of the reductive elimination
Bi
SON
F3C
XeF2 (1.0 eq) F 110 oCBi
SON
F3C
F
F
R
R
R
Fluorination of arylboron via Bi(III)/Bi(V) redox catalysis
Planas, O.; Wang, F.; Leutzsch, M.; Cornella, J. Science. 2020, 367, 313.
■ Mechanism study of the reductive elimination
FBi
SO
NCF3
F
F slower decay in the presence of Bu4NF
CD3Cl, 90 oC, 6hBi
SON
F3C
F
F
C-F bond R.E.
94% yield
proposed cationic intermediates
Bi
SON
F3C
PhF
FB F
F F
fast dissociation of labile BF4- ligand
CD3Cl, 60 oC, 5min
NMR, HRMS
Bi
SON
F3C
F
BF4
C-F bond R.E. F
85% yield
1.0 eq BF3·Et2OCH3Cl, -45 oC
5 min>99% yield
Fluorination of arylboron via Bi(III)/Bi(V) redox catalysis
Planas, O.; Wang, F.; Leutzsch, M.; Cornella, J. Science. 2020, 367, 313.
■ Fluoropyridinium as fluorinating reagent
CD3Cl, 60 oC, 2hBi
SON
F3C
F
BF4
F
85% yield
Bi
SON
F3C
NCl Cl
F
BF4
(1.2 eq)
Bi
SO
NF3C
F
N ClCl BF4
ligand exchange
Fluorination of arylboron via Bi(III)/Bi(V) redox catalysis
Planas, O.; Wang, F.; Leutzsch, M.; Cornella, J. Science. 2020, 367, 313.
■ Transmetallation of arylborone to Bi
Bi
SON
F3C
BF4
Bi
SON
F3C
Ph-B, KF, MeCN, 90 oC
B(OH)2
95% yield
Bpin
67% yield
B
72% yield
O
O
Me
Me
PhB
80% yield
OB
OB
O
Ph
Ph
Fluorination of arylboron via Bi(III)/Bi(V) redox catalysis
Planas, O.; Wang, F.; Leutzsch, M.; Cornella, J. Science. 2020, 367, 313.
■ Merging element steps together for Bi(III)/Bi(V) redox catalysis
Bi
SON
F3C
BF4
Bi
SON
F3C
Ph-B, KF, MeCN, 90 oC
CD3Cl, 60 oC, 2hBi
SON
F3C
NCl Cl
F
BF4
(1.2 eq)F
85% yield
Fluorination of arylboron via Bi(III)/Bi(V) redox catalysis
Planas, O.; Wang, F.; Leutzsch, M.; Cornella, J. Science. 2020, 367, 313.
■ Merging element steps together for Bi(III)/Bi(V) redox catalysis
Bi
SON
F3C
BF4
Bi
SON
F3C
Ph-B, KF, MeCN, 90 oC
Bpin F
Bi
SON
F3C
BF4
Bi(III) (10 mol%)NaF (5.0 eq), CDCl3, 90 oC
NCl Cl
F
BF4 (1.0 eq)
First Bi(III)/Bi(V) redox catalysis
What about Bi(I)/Bi(III) redox catalysis?
Wang, F.; Planas, O.; Cornella, J. JACS 2019, 141, 4235.
■ Bi(I) catalyzed transfer hydrogenation
Bi(I) (1 mol%)NH3BH3 (1.0 eq), H2O (1.0 eq)
THF, 35 oCN
NPh
PhN
NPh
Ph
H
H
N
BiN
tBu
tBu
Bi(I) catalyst
N
BiN
tBu
tBu
H
H
via Bi(III) hydride
What about Bi(I)/Bi(III) redox catalysis?
Wang, F.; Planas, O.; Cornella, J. JACS 2019, 141, 4235.
■ Bi(I) catalyzed transfer hydrogenation
Bi(I) (1 mol%)NH3BH3 (1.0 eq), H2O (1.0 eq)
THF, 35 oC
97% yield
NN
PhPh
NN
PhPh
H
H
N
BiN
tBu
tBu
Bi(I) catalyst
NN
H
H
Me
Me
99% yield
NN
H
H
CF3
F3C
98% yield
NN
H
HBr
99% yield
NN
H
H
NMe2
I
98% yield
NN
H
H
Me
Me
Me
MeNN
H H
99% yield
Transfer hydrogenation via Bi(I)/Bi(III) redox catalysis
Wang, F.; Planas, O.; Cornella, J. JACS 2019, 141, 4235.
■ Bi(I) catalyzed transfer hydrogenation of nitroarenes
Bi(I) (1 mol%)NH3BH3 (1.0 eq)
dioxane, 35 oC
97% yield
N
BiN
tBu
tBu
Bi(I) catalyst
NO2 N
H
Me
OH
N
H
Me
OH
88% yield
N
H
I
OH
67% yield
N
H
OH
82% yield
N
H
OH
75% yield
N
H
OH
22% yield
N
H
OH
Me
Me
Transfer hydrogenation via Bi(I)/Bi(III) redox catalysis
Wang, F.; Planas, O.; Cornella, J. JACS 2019, 141, 4235.
Bi(I) (1 mol%)NH3BH3 (1.0 eq), H2O (1.0 eq)
THF, 35 oCN
NPh
PhN
NPh
Ph
H
H
N
BiN
tBu
tBu
H
H
via Bi(III) hydride
Effect of water
Transfer hydrogenation via Bi(I)/Bi(III) redox catalysis
Wang, F.; Planas, O.; Cornella, J. JACS 2019, 141, 4235.
Bi(I) (1 mol%)Dn-NH3BH3 (1.0 eq), D2O
THF, 35 oC
NN
PhPh
NN
PhPh
H
H
N
BiN
tBu
tBu
H
H
via Bi(III) hydride
KIE experiments
Both N-H and B-H bonds are cleaved in the rate-determining step
Transfer hydrogenation via Bi(I)/Bi(III) redox catalysis
Wang, F.; Planas, O.; Cornella, J. JACS 2019, 141, 4235.
Bi(I) (1 mol%)NH3BH3 (1.0 eq), H2O
THF, 35 oC
Competition experiment study
■ azoarenes are not participating in the RDS of this transformation
■ Bi(I) and AB are both involved in the RDS
NN
H
H
Me
Me
NN
Me
Me
Bi(I) (1 mol%)NH3BH3 (1.0 eq), H2O
THF, 35 oC
NN
H
H
F
F
NN
F
F
Product 1:1 ratio observed
Transfer hydrogenation via Bi(I)/Bi(III) redox catalysis
Wang, F.; Planas, O.; Cornella, J. JACS 2019, 141, 4235.
■ Stoichiometric study for Bi(III)—H species
PhSiH
■ Bi(I) and H2 was detected during the reaction■ proton is from hydridic sources
N
BiN
tBu
tBu
H
H
putative Bi(III) hydrideintermediate
NN
PhPh
H
H
NN
PhPh
H
H
NN
PhPhN
BiN
tBu
tBu
F
F
N
BiN
tBu
tBu
Cl
Cl
NaBH3CNN
NPh
Ph
71% yield
98% yield
Transfer hydrogenation via Bi(I)/Bi(III) redox catalysis
Wang, F.; Planas, O.; Cornella, J. JACS 2019, 141, 4235.
■ Mass-spectrometry study for Bi(III)—H species
N
BiN
tBu
tBu
H
H
putative Bi(III) hydrideintermediate
N
BiN
tBu
tBu
20 mol%
NH3BH3 (1.0 equiv)
ND3BD3 (1.0 equiv)
N
BiN
tBu
tBu
H
HRMS-ESI
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