Post on 24-Apr-2018
The Chemistry of Frustrated Lewis Pairs
MacMillan Group Meeting
4 December 2013
Tracy Liu
B
RR
R
NR
RR
B
RR
R
NR
RR
B
RR
R
NR
RR B N
R
RR R
RR
BRR
RNR
RR B N
R
RR R
RR
BRR
RNR
RR B N
R
RR R
RR
H2H H
BRR
RNR
RR B N
R
RR R
RR
BRR
RNR
RR B N
R
RR R
RR
H2H H
heat
0
20
40
60
80
100
2000 2006 2009 2012
Num
ber
of P
ublic
atio
ns
■ 289 total publications in FLP chemistry
■ Leading Academics:Douglas W. Stephan, University of Toronto, CanadaGerhard Erker, Westfälische Wilhelms-Universität Münster, GermanyImre Pápai, Chemical Research Cent. of the Hungarian Acad. of Sciences, Hungary
Rapid Emergence of FLP Chemistry
N
Me
Me
BF3 BMe3No ReactionN
Me
Me
BF3
Brown, H. C.; Schlesinger, H. I. JACS, 1942, 64, 325-329.
1942 - Brown makes an interesting observation
The Advent of FLP Chemistry
N
Me
Me
BF3 BMe3No ReactionN
Me
Me
BF3
Brown, H. C.; Schlesinger, H. I. JACS, 1942, 64, 325-329.
1942 - Brown makes an interesting observation
The Advent of FLP Chemistry
Wittig, G.; Benz, E. Chem. Ber., 1959, 92, 1999-2013.
F
Br
Mg
PPh3BPh3
PPh3
BPh3
No formation of classical Lewis Acid/Base adduct
1942 - Brown makes an interesting observation
The Advent of FLP Chemistry
1959 - Wittig finds PPh3 and BPh3 does not form an adduct
Tochtermann, W. ACIE, 1966, 5, 351-371.
[Ph3C-]Na+
BPh3
Ph3C
BPh3
and Ph3C BPh3
no observation of polybutadiene
1942 - Brown makes an interesting observation
The Advent of FLP Chemistry
1959 - Wittig finds PPh3 and BPh3 does not form an adduct
1966 - Tochtermann reports Ph3C-
and BPh3 trap across olefins;coining of the term "FLP"
1942 - Brown makes an interesting observation
The Advent of FLP Chemistry
1959 - Wittig finds PPh3 and BPh3 does not form an adduct
1966 - Tochtermann reports Ph3C-
and BPh3 trap across olefins;
2006 - Stephan finds FLPscan reversibly split H2
coining of the term "FLP"
PH
Me
Me
Me
2
+
FF
FF
B(C6F5)2(Me3C6H2)2PF
H
FF
FF
B(C6F5)2(Me3C6H2)2PH
H
B(C6F5)3
Me2SiHCl
Welch, G. C.; San Juan, R. R.; Masuda, J. D.; Stephan, D. W. Science, 2006, 314, 1124-1126.
Welch, G. C.; San Juan, R. R.; Masuda, J. D.; Stephan, D. W. Science, 2006, 314, 1124-1126.
1942 - Brown makes an interesting observation
The Advent of FLP Chemistry
1959 - Wittig finds PPh3 and BPh3 does not form an adduct
1966 - Tochtermann reports Ph3C-
and BPh3 trap across olefins;
2006 - Stephan finds FLPscan reversibly split H2
coining of the term "FLP"
FF
FF
B(C6F5)2(Me3C6H2)2PH
H
heatFF
FF
B(C6F5)2(Me3C6H2)2PH2
Welch, G. C.; San Juan, R. R.; Masuda, J. D.; Stephan, D. W. Science, 2006, 314, 1124-1126.
1942 - Brown makes an interesting observation
The Advent of FLP Chemistry
1959 - Wittig finds PPh3 and BPh3 does not form an adduct
1966 - Tochtermann reports Ph3C-
and BPh3 trap across olefins;
2006 - Stephan finds FLPscan reversibly split H2
coining of the term "FLP"
FF
FF
B(C6F5)2(Me3C6H2)2PH
H
heatFF
FF
B(C6F5)2(Me3C6H2)2PH2
Greb, L.; Ona-Burgos, P.; Schirmer, B.; Grimme, S.; Stephan, D. W.; Paradies, J. ACIE, 2012, 51, 10164-10168.
1942 - Brown makes an interesting observation
The Advent of FLP Chemistry
1959 - Wittig finds PPh3 and BPh3 does not form an adduct
1966 - Tochtermann reports Ph3C- and BPh3 trap across olefins;
2006 - Stephan finds FLPscan reversibly split H2
coining of the term "FLP"2007 - FLPs catalytically
perform hydrogenations
Ph
NtBu
B(C6F5)2(tBu)2P
(5 mol %)1 atm H2 Ph
HNtBu
98%
Ph Ph
B(C6F5)3 (20 mol %)
5 bar H299%
Ph Ph
Me(C6F5)Ph2P (20 mol %)
Chase, P.A.; Welch, G. C.; Jurca, T.; Stephan, D. W. ACIE, 2007, 46, 8050-8053.
Mömming, C. M.; Otten, E.; Kehr, G.; Frölich, R.; Grimme, S.; Stephan, D. W.; Erker, G. ACIE, 2009, 48, 6643-6646.
1942 - Brown makes an interesting observation
The Advent of FLP Chemistry
1959 - Wittig finds PPh3 and BPh3 does not form an adduct
1966 - Tochtermann reports Ph3C- and BPh3 trap across olefins;
2006 - Stephan finds FLPscan reversibly split H2
coining of the term "FLP"2007 - FLPs catalytically
perform hydrogenations
2008 - FLPs reversiblybind CO2
tBu3P + B(C6F5)3
CO2, 25 ºCO
O
(tBu)3P B(C6F5)3
-CO2, 80 ºCvacuum, 5 hrs
Chen, D.; Wang, Y.; Klankermeyer, J. ACIE, 2010, 49, 9475-9578.
1942 - Brown makes an interesting observation
The Advent of FLP Chemistry
1959 - Wittig finds PPh3 and BPh3 does not form an adduct
1966 - Tochtermann reports Ph3C- and BPh3 trap across olefins;
2006 - Stephan finds FLPscan reversibly split H2
coining of the term "FLP"2007 - FLPs catalytically
perform hydrogenations
2008 - FLPs reversiblybind CO2
2010 - Asymmetrichydrogenationof imines with FLPs
N
OMe
Me Me
Me
B(C6F5)2
(5 mol %)
tBu3P (5 mol %)25 bar H2
HN
OMe
MeMe
>99%81% ee
Ph
1942 - Brown makes an interesting observation
The Advent of FLP Chemistry
1959 - Wittig finds PPh3 and BPh3 does not form an adduct
1966 - Tochtermann reports Ph3C- and BPh3 trap across olefins;
2006 - Stephan finds FLPscan reversibly split H2
coining of the term "FLP"2007 - FLPs catalytically
perform hydrogenations
2008 - FLPs reversiblybind CO2
2010 - Asymmetrichydrogenationof imines with FLPs
■ I. Theories on the Mechanism of H2 Activation
■ II. Applications of FLPs in Hydrogenation Reactionsand Storage of Small Molecules
1942 - Brown makes an interesting observation
The Advent of FLP Chemistry
1959 - Wittig finds PPh3 and BPh3 does not form an adduct
1966 - Tochtermann reports Ph3C- and BPh3 trap across olefins;
2006 - Stephan finds FLPscan reversibly split H2
coining of the term "FLP"2007 - FLPs catalytically
perform hydrogenations
2008 - FLPs reversiblybind CO2
2010 - Asymmetrichydrogenationof imines with FLPs
■ I. Theories on the Mechanism of H2 Activation
■ II. Applications of FLPs in Hydrogenation Reactionsand Storage of Small Molecules
Two Competing Models on the Mechanism of H2 Activation
R3P BR3
R
RR H
H
AR
RR
R
DR
R HH
RR
R
D → σ* donation σ → A donation
Electron Transfer Model
Electric Field Model
Initial Hypotheses on the Mechanism of H2 Activation
B(C6F5)3+tBu3P
Mes3P B(C6F5)3+
[tBu3PH][HB(C6F5)3]
[Mes3PH][HB(C6F5)3]
H2
H2
1 atm
1 atm
Welch, C.; Stephan, D. W. JACS, 2007, 129 , 1880-1881.
Initial Hypotheses on the Mechanism of H2 Activation
B(C6F5)3+tBu3P
Mes3P B(C6F5)3+
[tBu3PH][HB(C6F5)3]
[Mes3PH][HB(C6F5)3]
H2
H2
1 atm
1 atm
PR3 + BR3
BR3H
H
R3P
[R3PH][HBR3]
H H
BR3
R3P
LP (P) → σ* (H2)
σ (H2) → p (B)
Welch, C.; Stephan, D. W. JACS, 2007, 129 , 1880-1881.
■ Multiple H-bonds between C–H---F groups give rise to a preorganized complex
■ Non-directional dispersion forces between tBu and C6F5 groups render the complex flexible
First DFT Study on the Mechanism of H2 Activation
Rokob, T. A.; Hamza, A.; Stirling, A.; Soós, T.; Pápai, I. ACIE, 2008, 120 , 2469-2472.
tBu3P ------ B(C6F5)3
■ Located T.S. features a nearly linear P–H–H–B axis
■ H2 bond elongated from 0.74 A to 0.79 A indicative of an early T.S.
■ 10.4 kcal/mol higher than tBu3P---B(C6F5)3 + H2
First DFT Study on the Mechanism of H2 Activation
Rokob, T. A.; Hamza, A.; Stirling, A.; Soós, T.; Pápai, I. ACIE, 2008, 120 , 2469-2472.
tBu3P --- H–H --- B(C6F5)3
■ Discovered significant H2 polarization
■ Electron transfer proceeds via simultaneous tBu3P → σ∗(H2) and σ(H2) → B(C6F5)3 donation
First DFT Study on the Mechanism of H2 Activation
Rokob, T. A.; Hamza, A.; Stirling, A.; Soós, T.; Pápai, I. ACIE, 2008, 120 , 2469-2472.
tBu3P --- H–H --- B(C6F5)3
First DFT Study on the Mechanism of H2 Activation
Rokob, T. A.; Hamza, A.; Stirling, A.; Soós, T.; Pápai, I. ACIE, 2008, 120 , 2469-2472.
The Electron Transfer Model
■ Non-bonding interactions between bulky substituents lead to a higher E frustrated complex
First DFT Study on the Mechanism of H2 Activation
Rokob, T. A.; Hamza, A.; Stirling, A.; Soós, T.; Pápai, I. ACIE, 2008, 120 , 2469-2472.
The Electron Transfer Model
■ Frustration energy, ΔEt, decreases the activation energy and renders hydrogen splittingfacile and highly exothermic via reactant state destabilization
■ Non-bonding interactions between bulky substituents lead to a higher E frustrated complex
First DFT Study on the Mechanism of H2 Activation
Rokob, T. A.; Hamza, A.; Stirling, A.; Soós, T.; Pápai, I. ACIE, 2008, 120 , 2469-2472.
The Electron Transfer Model
■ Frustration energy, ΔEt, decreases the activation energy and renders hydrogen splittingfacile and highly exothermic via reactant state destabilization
■ Non-bonding interactions between bulky substituents stabilizes both the T.S. and product
■ Non-bonding interactions between bulky substituents lead to a higher E frustrated complex
BP
Mes
Mes
C6F5
C6F5
H HB
P
Mes
Mes
C6F5
C6F5
H2
Linear T.S. not possible for certain tethered FLPs
BP
Mes
Ph
Ph
Mes
BP
Mes
Mes
PhPh
HH
H2
An Alternative Mechanism of H2 Activation
Grimme, S.; Kruse, H.; Goerigk, L.; Erker, G. ACIE, 2010, 49, 1402-1405.
(C6F5)3B ---- PtBu3 + H2 (C6F5)2B PMes2+ H2
Calculated T.S. do not have a linear relationship along P–H–H–B axis
An Alternative Mechanism of H2 Activation
Grimme, S.; Kruse, H.; Goerigk, L.; Erker, G. ACIE, 2010, 49, 1402-1405.
Calculated T.S. employing a dispersion corrected DFT model:
2-D potential E surface for tBu3P + B(C6F5)3 system
An Alternative Mechanism of H2 Activation
Grimme, S.; Kruse, H.; Goerigk, L.; Erker, G. ACIE, 2010, 49, 1402-1405.
2 kcal/mol betweeneach line
incr. E
2 kcal/mol betweeneach line
incr. E
peak
An Alternative Mechanism of H2 Activation
Grimme, S.; Kruse, H.; Goerigk, L.; Erker, G. ACIE, 2010, 49, 1402-1405.
peak
An Alternative Mechanism of H2 Activation
Grimme, S.; Kruse, H.; Goerigk, L.; Erker, G. ACIE, 2010, 49, 1402-1405.
artificial T.S.
Pápai's non-dispersion corrected DFT model overestimated the P–B bond distance
resulting in a T.S. that is otherwise not present
An Alternative Mechanism of H2 Activation
Grimme, S.; Kruse, H.; Goerigk, L.; Erker, G. ACIE, 2010, 49, 1402-1405.
The Electric Field Model
R3P BR3
■ Neglect the FLP as a molecular speciesand replace it by an electric field
■ Polarization from electric field generated inthe interior of the FLP cavity allows for H2 splitting
F = Electric field strength (a.u.)(1 a.u. = 5.1422 x 1011 Vm-1)
Critical field strength needed for H2 splitting is 0.05 – 0.06 a.u.
An Alternative Mechanism of H2 Activation
Grimme, S.; Kruse, H.; Goerigk, L.; Erker, G. ACIE, 2010, 49, 1402-1405.
The Electric Field Model
R3P BR3
■ Neglect the FLP as a molecular speciesand replace it by an electric field
■ Polarization from electric field generated inthe interior of the FLP cavity allows for H2 splitting
F = Electric field strength (a.u.)(1 a.u. = 5.1422 x 1011 Vm-1)
Critical field strength needed for H2 splitting is 0.05 – 0.06 a.u.
An Alternative Mechanism of H2 Activation
Grimme, S.; Kruse, H.; Goerigk, L.; Erker, G. ACIE, 2010, 49, 1402-1405.
The Electric Field Model
P B
C6F5tBu
C6F5tBuC6F5tBu
0.04 - 0.06 a.u.
B
P
Mes
Mes
C6F5
C6F5
0.04 - 0.06 a.u.
An Alternative Mechanism of H2 Activation
Grimme, S.; Kruse, H.; Goerigk, L.; Erker, G. ACIE, 2010, 49, 1402-1405.
The Electric Field Model
■ H-bonding interactions form the FLP while non-directional dispersion forces instillflexibility allowing H2 entry – termed the "preparation step"
An Alternative Mechanism of H2 Activation
Grimme, S.; Kruse, H.; Goerigk, L.; Erker, G. ACIE, 2010, 49, 1402-1405.
The Electric Field Model
■ H-bonding interactions form the FLP while non-directional dispersion forces instillflexibility allowing H2 entry – termed the "preparation step"
■ Activation energy is the "preparation step"; after entrance H2 splitting is barrierless
An Alternative Mechanism of H2 Activation
Grimme, S.; Kruse, H.; Goerigk, L.; Erker, G. ACIE, 2010, 49, 1402-1405.
The Electric Field Model
■ H-bonding interactions form the FLP while non-directional dispersion forces instillflexibility allowing H2 entry – termed the "preparation step"
■ Activation energy is the "preparation step"; after entrance H2 splitting is barrierless
■ No molecular orbitals arguments invoked; believe this accounts for the similar reactivity of chemically different FLPs
The Electron Transfer Model Revisited
Rokob, T. A.; Bakó, I.; Stirling, A.; Hamza, A.; Pápai, I. JACS, 2013, 135 , 4425-4437.
P
tBu
tButBu
B
C6F5
C6F5C6F5
+ B
C6F5
C6F5C6F5
+ B
C6F4H
Mes C6F4H+
NC
NtBu
tBuN
The Electron Transfer Model Revisited
Rokob, T. A.; Bakó, I.; Stirling, A.; Hamza, A.; Pápai, I. JACS, 2013, 135 , 4425-4437.
P
tBu
tButBu
B
C6F5
C6F5C6F5
+ B
C6F5
C6F5C6F5
+ B
C6F4H
Mes C6F4H+
NC
NtBu
tBuN
The Electron Transfer Model Revisited
Rokob, T. A.; Bakó, I.; Stirling, A.; Hamza, A.; Pápai, I. JACS, 2013, 135 , 4425-4437.
■ At the "critical field" of 0.06 a.u., the activation energy is 75 kcal/mol
Grimme, S.; Kruse, H.; Goerigk, L.; Erker, G. ACIE, 2010, 49, 1402-1405.
F = Electric field strength (a.u.)(1 a.u. = 5.1422 x 1011 Vm-1)
The Electron Transfer Model Revisited
Rokob, T. A.; Bakó, I.; Stirling, A.; Hamza, A.; Pápai, I. JACS, 2013, 135 , 4425-4437.
■ At the "critical field" of 0.06 a.u., the activation energy is 75 kcal/mol
■ Only at higher electric fields, 0.09 a.u. and above, does the activation energy lowerto a reasonable range (20 kcal/mol or lower)
Grimme, S.; Kruse, H.; Goerigk, L.; Erker, G. ACIE, 2010, 49, 1402-1405.
F = Electric field strength (a.u.)(1 a.u. = 5.1422 x 1011 Vm-1)
The Electron Transfer Model Revisited
Rokob, T. A.; Bakó, I.; Stirling, A.; Hamza, A.; Pápai, I. JACS, 2013, 135 , 4425-4437.
■ At the "critical field" of 0.06 a.u., the activation energy is 75 kcal/mol
■ Only at higher electric fields, 0.09 a.u. and above, does the activation energy lowerto a reasonable range (20 kcal/mol or lower)
Grimme, S.; Kruse, H.; Goerigk, L.; Erker, G. ACIE, 2010, 49, 1402-1405.
F = Electric field strength (a.u.)(1 a.u. = 5.1422 x 1011 Vm-1)
■ Only at field strengths above 0.1 a.u., does H2 splitting become "barrierless"
The Electron Transfer Model Revisited
Rokob, T. A.; Bakó, I.; Stirling, A.; Hamza, A.; Pápai, I. JACS, 2013, 135 , 4425-4437.
P
tBu
tButBu
B
C6F5
C6F5C6F5
+ B
C6F5
C6F5C6F5
+ B
C6F4H
Mes C6F4H+
NC
NtBu
tBuN
The Electron Transfer Model Revisited
Rokob, T. A.; Bakó, I.; Stirling, A.; Hamza, A.; Pápai, I. JACS, 2013, 135 , 4425-4437.
P
tBu
tButBu
B
C6F5
C6F5C6F5
+ B
C6F5
C6F5C6F5
+ B
C6F4H
Mes C6F4H+
NC
NtBu
tBuN
The Electron Transfer Model Revisited
Rokob, T. A.; Bakó, I.; Stirling, A.; Hamza, A.; Pápai, I. JACS, 2013, 135 , 4425-4437.
P
tBu
tButBu
B
C6F5
C6F5C6F5
+ B
C6F5
C6F5C6F5
+ B
C6F4H
Mes C6F4H+
NC
NtBu
tBuN
EFs within FLP cavities are not homogeneous and are not always strong enough to effect H2 splitting
The Electron Transfer Model Revisited
Rokob, T. A.; Bakó, I.; Stirling, A.; Hamza, A.; Pápai, I. JACS, 2013, 135 , 4425-4437.
P
tBu
tButBu
NC
NtBu tBu
N P BMes
MesC6F5
C6F5 B C6F5
C6F5N
MeMe
MeMe P B
Ph
Ph
tBu
tBu
1 2 3 4 5 6+ B(C6F5)3+ B(C6F5)3+ B(C6F5)3
The Electron Transfer Model Revisited
Rokob, T. A.; Bakó, I.; Stirling, A.; Hamza, A.; Pápai, I. JACS, 2013, 135 , 4425-4437.
P
tBu
tButBu
NC
NtBu tBu
N P BMes
MesC6F5
C6F5 B C6F5
C6F5N
MeMe
MeMe P B
Ph
Ph
tBu
tBu
1 2 3 4 5 6+ B(C6F5)3+ B(C6F5)3+ B(C6F5)3
For none of the FLPs studied is the EF along the H2 axis high enough to permit H2 splitting
0.09 a.u.
The Electron Transfer Model Revisited
Rokob, T. A.; Bakó, I.; Stirling, A.; Hamza, A.; Pápai, I. JACS, 2013, 135 , 4425-4437.
HH
R
RR H
H
AR
RR
R
DR
R HH
RR
R
HH
■ Use of dispersion corrected DFT basis set results in a generally bent D–H–H–A geometry
■ Deviation from ideal 180º D---H2 angle and 90º H2---A angle due to polarization of the
explained by frontier orbitals aligning themselves for optimal orbital overlap
σ / σ* orbitals of H2
D → σ* donation
σ → A donation
1942 - Brown makes an interesting observation
The Advent of FLP Chemistry
1959 - Wittig finds PPh3 and BPh3 does not form an adduct
1966 - Tochtermann reports Ph3C- and BPh3 trap across olefins;
2006 - Stephan finds FLPscan reversibly split H2
coining of the term "FLP"2007 - FLPs catalytically
perform hydrogenations
2008 - FLPs reversiblybind CO2
2010 - Asymmetrichydrogenationof imines with FLPs
■ I. Theories on the Mechanism of H2 Activation
■ II. Applications of FLPs in Hydrogenation Reactionsand Storage of Small Molecules
The First Example of Catalytic Hydrogenations with FLPs
Chase, P. A.; Welch, C.; Jurca, T.; Stephan, D. W. ACIE, 2007, 46, 8050-8053.
Hydrogenation of Imines, Nitriles, and Aziridines
F F
F F
(C6F5)2B PR22 R = tBu1 R = Mes N
Ph
tBuHN
Ph
tBu5 mol % cat.
1 atm H2
79% (1)98% (2)
80 ºC
The First Example of Catalytic Hydrogenations with FLPs
Chase, P. A.; Welch, C.; Jurca, T.; Stephan, D. W. ACIE, 2007, 46, 8050-8053.
Hydrogenation of Imines, Nitriles, and Aziridines
F F
F F
(C6F5)2B PR22 R = tBu1 R = Mes N
Ph
tBuHN
Ph
tBu5 mol % cat.
1 atm H2
79% (1)98% (2)
80 ºC
N
Ph
SO2PhN
Ph
Ph
Ph NPh
PhPh
97% (1)87% (2)
88% (1) 98% (1)
■ Catalytic hydrogenation only possible for sterically hindered imines
The First Example of Catalytic Hydrogenations with FLPs
Chase, P. A.; Welch, C.; Jurca, T.; Stephan, D. W. ACIE, 2007, 46, 8050-8053.
Hydrogenation of Imines, Nitriles, and Aziridines
N
Ph
Ph HN
Ph
Ph
FF
FF
B(C6F5)2Mes2P
5 mol %
5 atm H2120 ºC 5%
■ Catalytic hydrogenation only possible for sterically hindered imines
The First Example of Catalytic Hydrogenations with FLPs
Chase, P. A.; Welch, C.; Jurca, T.; Stephan, D. W. ACIE, 2007, 46, 8050-8053.
Hydrogenation of Imines, Nitriles, and Aziridines
N
Ph
Ph HN
Ph
Ph
FF
FF
B(C6F5)2Mes2P
5 mol %
5 atm H2120 ºC 5%
FF
FF
B(C6F5)2Mes2PN Bn
Bn H
adduct formation between Lewis Basic productand FLP shuts down catalytic activity
■ Catalytic hydrogenation only possible for sterically hindered imines
The First Example of Catalytic Hydrogenations with FLPs
Chase, P. A.; Welch, C.; Jurca, T.; Stephan, D. W. ACIE, 2007, 46, 8050-8053.
Hydrogenation of Imines, Nitriles, and Aziridines
N
Ph
Ph HN
Ph
Ph
FF
FF
B(C6F5)2Mes2P
5 mol %
5 atm H2120 ºC 5%
N
Ph
Ph N
Ph
Ph
FF
FF
B(C6F5)2Mes2P
5 mol %
5 atm H2120 ºC 57%
■ Protecting Imine with B(C6F5)3 recovers catalytic activity
(C6F5)3B (C6F5)3B
■ Catalytic hydrogenation only possible for B(C6F5)3 protected nitriles
The First Example of Catalytic Hydrogenations with FLPs
Chase, P. A.; Welch, C.; Jurca, T.; Stephan, D. W. ACIE, 2007, 46, 8050-8053.
Hydrogenation of Imines, Nitriles, and Aziridines
N HN
R
B(C6F5)3
FF
FF
B(C6F5)2Mes2P
5 mol %
5 atm H2120 ºC
R = Me, 75%
B(C6F5)3
R
Only the amine is isolated (cannot isolate imine)
R = Ph, 84%
The First Example of Catalytic Hydrogenations with FLPs
Chase, P. A.; Welch, C.; Jurca, T.; Stephan, D. W. ACIE, 2007, 46, 8050-8053.
Hydrogenation of Imines, Nitriles, and Aziridines
FF
FF
B(C6F5)2Mes2P
FF
FF
B(C6F5)2Mes2PH
H
H2
The First Example of Catalytic Hydrogenations with FLPs
Chase, P. A.; Welch, C.; Jurca, T.; Stephan, D. W. ACIE, 2007, 46, 8050-8053.
Hydrogenation of Imines, Nitriles, and Aziridines
FF
FF
B(C6F5)2Mes2P
FF
FF
B(C6F5)2Mes2P
FF
FF
B(C6F5)2Mes2PH
H
H2
HN
Ph
RH
proton transfer
N
Ph
R
The First Example of Catalytic Hydrogenations with FLPs
Chase, P. A.; Welch, C.; Jurca, T.; Stephan, D. W. ACIE, 2007, 46, 8050-8053.
Hydrogenation of Imines, Nitriles, and Aziridines
FF
FF
B(C6F5)2Mes2P
FF
FF
B(C6F5)2Mes2P
FF
FF
B(C6F5)2Mes2PH
H
H2
HN
Ph
RH
proton transfer
N
Ph
R
HN
Ph
R
The First Example of Catalytic Hydrogenations with FLPs
Chase, P. A.; Welch, C.; Jurca, T.; Stephan, D. W. ACIE, 2007, 46, 8050-8053.
Hydrogenation of Imines, Nitriles, and Aziridines
FF
FF
B(C6F5)2Mes2P
FF
FF
B(C6F5)2Mes2P
FF
FF
B(C6F5)2Mes2PH
H
H2
HN
Ph
RH
proton transfer
N
Ph
R
HN
Ph
R
Proton transfer precedes hydride deliveryIncreased rates with electron rich imines (R = tBu, 1 hr vs. R = SO2Ph, >10 hrs)
The First Example of Catalytic Hydrogenations with FLPs
Chase, P. A.; Welch, C.; Jurca, T.; Stephan, D. W. ACIE, 2007, 46, 8050-8053.
Hydrogenation of Imines, Nitriles, and Aziridines
FF
FF
B(C6F5)2Mes2P
FF
FF
B(C6F5)2Mes2PH
H
H2
The First Example of Catalytic Hydrogenations with FLPs
Chase, P. A.; Welch, C.; Jurca, T.; Stephan, D. W. ACIE, 2007, 46, 8050-8053.
Hydrogenation of Imines, Nitriles, and Aziridines
FF
FF
B(C6F5)2Mes2P
FF
FF
B(C6F5)2Mes2P
FF
FF
B(C6F5)2Mes2PH
H
H2
N
Ph
R(C6F5)3B
hydride delivery
N
Ph
R(C6F5)3B
H H
The First Example of Catalytic Hydrogenations with FLPs
Chase, P. A.; Welch, C.; Jurca, T.; Stephan, D. W. ACIE, 2007, 46, 8050-8053.
Hydrogenation of Imines, Nitriles, and Aziridines
FF
FF
B(C6F5)2Mes2P
FF
FF
B(C6F5)2Mes2P
FF
FF
B(C6F5)2Mes2PH
H
H2
N
Ph
R(C6F5)3B
hydride delivery
N
Ph
R
N
Ph
R(C6F5)3B
(C6F5)3B
H H
H
The First Example of Catalytic Hydrogenations with FLPs
Chase, P. A.; Welch, C.; Jurca, T.; Stephan, D. W. ACIE, 2007, 46, 8050-8053.
Hydrogenation of Imines, Nitriles, and Aziridines
FF
FF
B(C6F5)2Mes2P
FF
FF
B(C6F5)2Mes2P
FF
FF
B(C6F5)2Mes2PH
H
H2
N
Ph
R(C6F5)3B
hydride delivery
N
Ph
R
N
Ph
R
Hydride delivery precedes proton transfer
(C6F5)3B
(C6F5)3B
H H
H
An Improved FLP
Spies, P.; Schwendemann, S.; Lange, S.; Kehr, G.; Fröhlich, R.; Erker, G. ACIE, 2008, 47, 7543-7546.
Hydrogenation of Ketimines and Enamines
Mes2P B(C6F5)2
H2Mes2P
B(C6F5)3
H
H
NtBu
Ph
Mes2P B(C6F5)2
2.5 bar H2r.t.
HNtBu
Ph
87%
20 mol %
An Improved FLP
Spies, P.; Schwendemann, S.; Lange, S.; Kehr, G.; Fröhlich, R.; Erker, G. ACIE, 2008, 47, 7543-7546.
Hydrogenation of Ketimines and Enamines
Mes2P B(C6F5)2
H2Mes2P
B(C6F5)3
H
H
NtBu
Ph
N
MePh
tBu
Mes2P B(C6F5)2
2.5 bar H2r.t.
HNtBu
Ph87%
20 mol %
(5 mol %)70%
NN N
O
(10 mol %)70%
(5 mol %)70%
(3 mol %)70%
Catalytic Hydrogenations Using only B(C6F5)3
Chase, P. A.; Jurca, T.; Stephan, D. W. Chem. Comm., 2008, 1701-1703.
Hydrogenation of Imines
NtBu
Ph4 atm H2
B(C6F5)3 (cat.)
toluene, 25 ºC
N
Ph
tBu(C6F5)3B
4 atm H2toluene, 80 ºC
H2NtBu
PhHB(C6F5)3
Catalytic Hydrogenations Using only B(C6F5)3
Chase, P. A.; Jurca, T.; Stephan, D. W. Chem. Comm., 2008, 1701-1703.
Hydrogenation of Imines
NtBu
Ph4 atm H2
B(C6F5)3 (cat.)
toluene, 25 ºC
N
Ph
tBu(C6F5)3B
4 atm H2toluene, 80 ºC
H2NtBu
PhHB(C6F5)3
Isolation of zwitterion suggests adduct formation with the product is reversibleand that the B(C6F5)3 catalyst can be recycled
Catalytic Hydrogenations Using only B(C6F5)3
Chase, P. A.; Jurca, T.; Stephan, D. W. Chem. Comm., 2008, 1701-1703.
Hydrogenation of Imines
NtBu
Ph4 atm H2
B(C6F5)3 (cat.)
toluene, 25 ºC
N
Ph
tBu(C6F5)3B
4 atm H2toluene, 80 ºC
H2NtBu
PhHB(C6F5)3
Isolation of zwitterion suggests adduct formation with the product is reversible
NtBu
Ph 5 atm H2120 ºC
HNtBu
Ph
89%
5 mol % B(C6F5)3
and that the B(C6F5)3 catalyst can be recycled
Catalytic Hydrogenations Using only B(C6F5)3
Chase, P. A.; Jurca, T.; Stephan, D. W. Chem. Comm., 2008, 1701-1703.
Hydrogenation of Imines
NtBu
Ph4 atm H2
B(C6F5)3 (cat.)
toluene, 25 ºC
N
Ph
tBu(C6F5)3B
4 atm H2toluene, 80 ºC
H2NtBu
PhHB(C6F5)3
Isolation of zwitterion suggests adduct formation with the product is reversibleand that the B(C6F5)3 catalyst can be recycled
H2 +N
R
R'
NR
R'
HHB(C6F5)3
B(C6F5)3
Catalytic Hydrogenations Using only B(C6F5)3
Chase, P. A.; Jurca, T.; Stephan, D. W. Chem. Comm., 2008, 1701-1703.
Hydrogenation of Imines
NtBu
Ph4 atm H2
B(C6F5)3 (cat.)
toluene, 25 ºC
N
Ph
tBu(C6F5)3B
4 atm H2toluene, 80 ºC
H2NtBu
PhHB(C6F5)3
Isolation of zwitterion suggests adduct formation with the product is reversibleand that the B(C6F5)3 catalyst can be recycled
H2 +N
R
R'
NR
R'
HHB(C6F5)3
N
R'
B(C6F5)3
H
HR
B(C6F5)3
Catalytic Hydrogenations Using only B(C6F5)3
Chase, P. A.; Jurca, T.; Stephan, D. W. Chem. Comm., 2008, 1701-1703.
Hydrogenation of Imines
NtBu
Ph4 atm H2
B(C6F5)3 (cat.)
toluene, 25 ºC
N
Ph
tBu(C6F5)3B
4 atm H2toluene, 80 ºC
H2NtBu
PhHB(C6F5)3
Isolation of zwitterion suggests adduct formation with the product is reversibleand that the B(C6F5)3 catalyst can be recycled
H2 +N
R
R'
NR
R'
HHB(C6F5)3
N
R'
B(C6F5)3
H
HR
NHR
R'
B(C6F5)3
Expanding the Scope to Oxygenated Substrates
Wang, H.; Fröhlich, R.; Kehr, G.; Erker, G. Chem. Comm., 2008, 5966-5968.
Hydrogenation of Silyl Enol Ethers
PPh2 PPh2 PPh2 PPh2H
HB(C6F5)3
H2, r.t.
–H2, 60 ºC
Expanding the Scope to Oxygenated Substrates
Wang, H.; Fröhlich, R.; Kehr, G.; Erker, G. Chem. Comm., 2008, 5966-5968.
Hydrogenation of Silyl Enol Ethers
PPh2 PPh2 PPh2 PPh2H
HB(C6F5)3
H2, r.t.
–H2, 60 ºC
R
OTMS
R
OTMS
R'
20 mol % cat.
2 bar H2, r.t.
Expanding the Scope to Oxygenated Substrates
Wang, H.; Fröhlich, R.; Kehr, G.; Erker, G. Chem. Comm., 2008, 5966-5968.
Hydrogenation of Silyl Enol Ethers
PPh2 PPh2 PPh2 PPh2H
HB(C6F5)3
H2, r.t.
–H2, 60 ºC
OTMS
Ph
OTMS
tBu
OTMS OTMS
Me
OTMS
R
OTMS
R
OTMS20 mol % cat.
2 bar H2, r.t.
93% 89% 86% 85% >99%
B(C6F5)3
R'R
Studies of Hantzsch Ester with B(C6F5)3 Unveils New Substrates
Geier, S. J.; Chase, P. A.; Stephan, D. W. Chem. Comm., 2010, 46, 4884-4886.
Hydrogenation of N-heterocycles
NH
Me Me
O
OEt
O
EtO
NH
Me Me
O
OEt
O
EtO B(C6F5)3 HB(C6F5)3
-40 ºC NH
Me Me
O
OEt
O
EtO
-20 ºCH
B(C6F5)3
60% 55%(70% at r.t.)
Webb, J. D.; Laberge, V. S.; Geier, S. J.; Stephan, D. W.; Crudden, C. M. Chem. Eur. J., 2010, 16 , 4895-4902.
Studies of Hantzsch Ester with B(C6F5)3 Unveils New Substrates
Geier, S. J.; Chase, P. A.; Stephan, D. W. Chem. Comm., 2010, 46, 4884-4886.
Hydrogenation of N-heterocycles
NH
Me Me
O
OEt
O
EtO
NH
Me Me
O
OEt
O
EtO B(C6F5)3 HB(C6F5)3
-40 ºC NH
Me Me
O
OEt
O
EtO
-20 ºCH
B(C6F5)3
60% 55%(70% at r.t.)
Webb, J. D.; Laberge, V. S.; Geier, S. J.; Stephan, D. W.; Crudden, C. M. Chem. Eur. J., 2010, 16 , 4895-4902.
Observation of hydride delivery into pyridinium inspiredexperimentation with N-heterocycle substrates
Studies of Hantzsch Ester with B(C6F5)3 Unveils New Substrates
Geier, S. J.; Chase, P. A.; Stephan, D. W. Chem. Comm., 2010, 46, 4884-4886.
Hydrogenation of N-heterocycles
NH
Me Me
O
OEt
O
EtO
NH
Me Me
O
OEt
O
EtO B(C6F5)3 HB(C6F5)3
-40 ºC NH
Me Me
O
OEt
O
EtO
-20 ºCH
B(C6F5)3
60% 55%(70% at r.t.)
Webb, J. D.; Laberge, V. S.; Geier, S. J.; Stephan, D. W.; Crudden, C. M. Chem. Eur. J., 2010, 16 , 4895-4902.
Observation of hydride delivery into pyridinium inspiredexperimentation with N-heterocycle substrates
N
5 mol % B(C6F5)3
4 atm H2, 2 hrs, r.t. NH80%
NH
HB(C6F5)3
Studies of Hantzsch Ester with B(C6F5)3 Unveils New Substrates
Geier, S. J.; Chase, P. A.; Stephan, D. W. Chem. Comm., 2010, 46, 4884-4886.
Hydrogenation of N-heterocycles
NH
Me Me
O
OEt
O
EtO
NH
Me Me
O
OEt
O
EtO B(C6F5)3 HB(C6F5)3
-40 ºC NH
Me Me
O
OEt
O
EtO
-20 ºCH
B(C6F5)3
60% 55%
Webb, J. D.; Laberge, V. S.; Geier, S. J.; Stephan, D. W.; Crudden, C. M. Chem. Eur. J., 2010, 16 , 4895-4902.
Observation of hydride delivery into pyridinium inspiredexperimentation with N-heterocycle substrates
N
5 mol % B(C6F5)3
2 hrs, r.t. NH80%
NH
Ph NH
Me NH
MeN
NH
80% 74% 88% 84%
Aromatic Hydrogenation
Mahdi, T.; Heiden, Z. M.; Grimme, S.; Stephan, D. W. JACS, 2012, 134 , 4088-4091.
Hydrogenation of Anilines to Cyclohexylamines
NHtBu
Ph
B(C6F5)3
H2, 25 ºCNH2
tBu
PhHB(C6F5)3
110 ºC
H2NH2
tBu
HB(C6F5)3
93%
Aromatic Hydrogenation
Mahdi, T.; Heiden, Z. M.; Grimme, S.; Stephan, D. W. JACS, 2012, 134 , 4088-4091.
Hydrogenation of Anilines to Cyclohexylamines
NHtBu
Ph
B(C6F5)3
H2, 25 ºCNH2
tBu
PhHB(C6F5)3
110 ºC
H2NH2
tBu
HB(C6F5)3
93%
NH2
HB(C6F5)3
NH2iPr
HB(C6F5)3
Me
NH2iPr
HB(C6F5)3
OMe
NH2iPr
Me MeHB(C6F5)3
65%, 96 hrs 77%, 36 hrs 61%, 36 hrs 48%, 72 hrs
Aromatic Hydrogenation
Mahdi, T.; Heiden, Z. M.; Grimme, S.; Stephan, D. W. JACS, 2012, 134 , 4088-4091.
Hydrogenation of Anilines to Cyclohexylamines
NHtBu
Ph
B(C6F5)3
H2, 25 ºCNH2
tBu
PhHB(C6F5)3
110 ºC
H2NH2
tBu
HB(C6F5)3
93%
NH2
HB(C6F5)3
NH2iPr
HB(C6F5)3
Me
NH2iPr
HB(C6F5)3
OMe
NH2iPr
Me MeHB(C6F5)3
65%, 96 hrs 77%, 36 hrs 61%, 36 hrs 48%, 72 hrs
NPh
PhPhPh
Ph
H2N HB(C6F5)3
50%, 96 hrs
5 mol % B(C6F5)3
H2, 110 ºC
Hydrogenation of Non-Polar Substrates
Greb, L.; Ona-Burgos, P.; Schirmer, B.; Grimme, S.; Stephan, D. W.; Paradies, J. ACIE, 2012, 51, 10164-10168.
Hydrogenation of Olefins
(C6F5)Ph2P B(C6F5)3 [(C6F5)Ph2PH] [HB(C6F5)3]+H2
cation posseses much greater bronsted acidity
Hydrogenation of Non-Polar Substrates
Greb, L.; Ona-Burgos, P.; Schirmer, B.; Grimme, S.; Stephan, D. W.; Paradies, J. ACIE, 2012, 51, 10164-10168.
Hydrogenation of Olefins
(C6F5)Ph2P B(C6F5)3 [(C6F5)Ph2PH] [HB(C6F5)3]+H2
cation posseses much greater bronsted acidity
Ph
Ph
20 mol % (C6F5)Ph2P20 mol % B(C6F5)3 Ph
PhMe
5 bar H2, r.t.
99%
Hydrogenation of Non-Polar Substrates
Greb, L.; Ona-Burgos, P.; Schirmer, B.; Grimme, S.; Stephan, D. W.; Paradies, J. ACIE, 2012, 51, 10164-10168.
Hydrogenation of Olefins
(C6F5)Ph2P B(C6F5)3 [(C6F5)Ph2PH] [HB(C6F5)3]+H2
cation posseses much greater bronsted acidity
Ph
Ph
20 mol % (C6F5)Ph2P20 mol % B(C6F5)3 Ph
PhMe
5 bar H2, r.t.
99%
Ph
Ph
Ph
PhMe
NPh
Ph
Me
H HB(C6F5)3
HB(C6F5)3
hydride delivery
Friedel Crafts
Ph2NMeNMePh
PhMe
Ph
Ph
PhMe
69%
31%
Hydrogenation of Non-Polar Substrates
Greb, L.; Ona-Burgos, P.; Schirmer, B.; Grimme, S.; Stephan, D. W.; Paradies, J. ACIE, 2012, 51, 10164-10168.
Hydrogenation of Olefins
R
R
R
RMe HB(C6F5)3
[(C6F5)Ph2PH] [HB(C6F5)3]
proton transfer hydride delivery
R
RMe
Hydrogenation of Non-Polar Substrates
Greb, L.; Ona-Burgos, P.; Schirmer, B.; Grimme, S.; Stephan, D. W.; Paradies, J. ACIE, 2012, 51, 10164-10168.
Hydrogenation of Olefins
R
R
R
RMe HB(C6F5)3
[(C6F5)Ph2PH] [HB(C6F5)3]
proton transfer hydride delivery
R
RMe
Me Me
Me
96% 85%
Hydrogenation of Non-Polar Substrates
Greb, L.; Ona-Burgos, P.; Schirmer, B.; Grimme, S.; Stephan, D. W.; Paradies, J. ACIE, 2012, 51, 10164-10168.
Hydrogenation of Olefins
R
R
R
RMe HB(C6F5)3
[(C6F5)Ph2PH] [HB(C6F5)3]
proton transfer hydride delivery
R
RMe
Me Me Me
Me MeO
96% 85% 30%
Hydrogenation of Non-Polar Substrates
Greb, L.; Ona-Burgos, P.; Schirmer, B.; Grimme, S.; Stephan, D. W.; Paradies, J. ACIE, 2012, 51, 10164-10168.
Hydrogenation of Olefins
R
R
R
RMe HB(C6F5)3
[(C6F5)Ph2PH] [HB(C6F5)3]
proton transfer hydride delivery
R
RMe
Me Me Me
Me MeO
Me
Cl
96% 85% 30% 10%
Hydrogenation of Non-Polar Substrates
Greb, L.; Ona-Burgos, P.; Schirmer, B.; Grimme, S.; Stephan, D. W.; Paradies, J. ACIE, 2012, 51, 10164-10168.
Hydrogenation of Olefins
R
R
R
RMe HB(C6F5)3
[(C6F5)Ph2PH] [HB(C6F5)3]
proton transfer hydride delivery
R
RMe
Me Me Me
Me MeO
Me
Cl
TMSMe
96% 85% 30% 10% 95%
Hydrogenation of Non-Polar Substrates
Greb, L.; Ona-Burgos, P.; Schirmer, B.; Grimme, S.; Stephan, D. W.; Paradies, J. ACIE, 2012, 51, 10164-10168.
Hydrogenation of Olefins
R
R
R
RMe HB(C6F5)3
[(C6F5)Ph2PH] [HB(C6F5)3]
proton transfer hydride delivery
R
RMe
Me Me Me
Me MeO
Me
Cl
TMSMe
Me Me
Me
Me Me
96% 85% 30% 10% 95%
99%
99%
Hydrogenation of Non-Polar Substrates
Chernichenko, K.; Madarász, A.; Pápai, I.; Nieger, M.; Leskela, M.; Repo, T. Nat. Chem., 2013, 5, 718-723.
Hydrogenation of Alkynes to Cis-Alkenes
R'R
NMe2
B
C6F5
H
NMe2
B
C6F5
R'
R
H
Hydrogenation of Non-Polar Substrates
Chernichenko, K.; Madarász, A.; Pápai, I.; Nieger, M.; Leskela, M.; Repo, T. Nat. Chem., 2013, 5, 718-723.
Hydrogenation of Alkynes to Cis-Alkenes
R'R
NMe2
B
C6F5
H
NMe2
B
C6F5
R'
R
H
N
BC6F5
R'
R
H
Me Me
H
H
H2
Hydrogenation of Non-Polar Substrates
Chernichenko, K.; Madarász, A.; Pápai, I.; Nieger, M.; Leskela, M.; Repo, T. Nat. Chem., 2013, 5, 718-723.
Hydrogenation of Alkynes to Cis-Alkenes
R'R
NMe2
B
C6F5
H
NMe2
B
C6F5
R'
R
H
N
BC6F5
R'
R
H
Me Me
H
H
H
R
R'H
H2
Hydrogenation of Non-Polar Substrates
Chernichenko, K.; Madarász, A.; Pápai, I.; Nieger, M.; Leskela, M.; Repo, T. Nat. Chem., 2013, 5, 718-723.
Hydrogenation of Alkynes to Cis-Alkenes
R'R
NMe2
B
C6F5
H
NMe2
B
C6F5
R'
R
H
N
BC6F5
R'
R
H
Me Me
H
H
H
R
R'H
H2
NMe2
B
C6F5
C6F5
N
BC6F5
Me Me
H
H
FF
F
FF
H2
80 ºC
Hydrogenation of Non-Polar Substrates
Chernichenko, K.; Madarász, A.; Pápai, I.; Nieger, M.; Leskela, M.; Repo, T. Nat. Chem., 2013, 5, 718-723.
Hydrogenation of Alkynes to Cis-AlkenesNMe2
B
C6F5
C6F5
N
BC6F5
Me Me
H
H
FF
F
FF
H2
80 ºC D2NMe2
B
C6F5
D
H
R
R'D
+
R'R
NMe2
B
C6F5
H
NMe2
B
C6F5
R'
R
H
N
BC6F5
R'
R
H
Me Me
H
H
H
R
R'H
H2
NOMe
MePh
Chen, D.; Wang, Y.; Klankermeyer, J. ACIE, 2010, 49, 9475-9578.
N
OMe
Me Me
Me
B(C6F5)2
(5 mol %)
tBu3P (5 mol %)25 bar H2
HN
OMe
MeMe
>99%81% ee
Asymmetric Catalytic HydrogenationHydrogenation of Imines
Me Me
Me
BC6F5
H
F FF
FF
Me Me
Me
BH
C6F5
NMe
FF F
FF
favored approach disfavored approach
Ph
tBu3P + B(C6F5)3
CO2, 25 ºCO
O
(tBu)3P B(C6F5)3
80 ºCvacuum, 5 hrs
Applications in Green Chemistry
Mömming, C. M.; Otten, E.; Kehr, G.; Fröhlich, R.; Grimme, S.; Stephan, D. W.; Erker, G. ACIE, 2009, 48, 6643-6646.
Reversible CO2 Binding
Mes2P
B(C6F5)3
Mes2P B(C6F5)3
CO2, 25 ºC
CH2Cl2, > -20 ºC
-CO2
-CO2
OO
Mes2P B(C6F5)3
87%
79%
Applications in Green Chemistry
Sajid, M. et. al. Chem. Sci., 2013, 4, 213-219.
SO2 and N2O Binding
tBu3P + B(C6F5)3
SO2, 25 ºCS O
O
(tBu)3P B(C6F5)3
Mes2P
B(C6F5)3
Mes2P B(C6F5)3
SO2, -75 ºCS O
O
Mes2P B(C6F5)3
80%
83%
*
■ SO2 is a major air pollutant, precursor to acid rain
Applications in Green Chemistry
Sajid, M. et. al. Chem. Sci., 2013, 4, 213-219.
SO2 and N2O Binding
tBu3P + B(C6F5)3
SO2, 25 ºCS O
O
(tBu)3P B(C6F5)3
Mes2P
B(C6F5)3
Mes2P B(C6F5)3
SO2, -75 ºCS O
O
Mes2P B(C6F5)3
80%
83%
*
■ SO2 is a major air pollutant, precursor to acid rain
■ N2O is a minor constituent in the atmosphere, but ~300x more potent as a greenhouse gas
tBu3P + B(C6F5)3
N2O, 25 ºCO
B(C6F5)3
76%
NN
(tBu)3P
Otten, E.; Neu, R. C.; Stephan, D. W. JACS, 2009, 131 , 9918-9919.
Applications in Green Chemistry
Berkefeld, A.; Piers, W. E.; Parvez, M. JACS, 2010, 132 , 10660-10661.
Converting CO2 to Fuels
■ Addition of Et3SiH to CO2 in the presence of an FLP efficiently reduces CO2 to CH4
HB(C6F5)3NH2
MeMe
MeMe
Applications in Green Chemistry
Berkefeld, A.; Piers, W. E.; Parvez, M. JACS, 2010, 132 , 10660-10661.
Converting CO2 to Fuels
■ Addition of Et3SiH to CO2 in the presence of an FLP efficiently reduces CO2 to CH4
HB(C6F5)3NH2
MeMe
MeMe
OO B(C6F5)3
HTMPH
CO2
Applications in Green Chemistry
Berkefeld, A.; Piers, W. E.; Parvez, M. JACS, 2010, 132 , 10660-10661.
Converting CO2 to Fuels
■ Addition of Et3SiH to CO2 in the presence of an FLP efficiently reduces CO2 to CH4
HB(C6F5)3NH2
MeMe
MeMe
Et3SiH + B(C6F5)3
HEt3Si B(C6F5)3
OO B(C6F5)3
HTMPH
CO2
OO SiEt3
H
Applications in Green Chemistry
Berkefeld, A.; Piers, W. E.; Parvez, M. JACS, 2010, 132 , 10660-10661.
Converting CO2 to Fuels
■ Addition of Et3SiH to CO2 in the presence of an FLP efficiently reduces CO2 to CH4
HB(C6F5)3NH2
MeMe
MeMe
Et3SiH + B(C6F5)3
HEt3Si B(C6F5)3
OO B(C6F5)3
HTMPH
CO2
OO SiEt3
H
OO SiEt3
Et3SiH
H
HEt3Si B(C6F5)3 –B(C6F5)3
Applications in Green Chemistry
Berkefeld, A.; Piers, W. E.; Parvez, M. JACS, 2010, 132 , 10660-10661.
Converting CO2 to Fuels
■ Addition of Et3SiH to CO2 in the presence of an FLP efficiently reduces CO2 to CH4
HB(C6F5)3NH2
MeMe
MeMe
Et3SiH + B(C6F5)3
HEt3Si B(C6F5)3
OO B(C6F5)3
HTMPH
CO2
OO SiEt3
H
OO SiEt3
Et3SiH
H
HEt3Si B(C6F5)3
HEt3Si B(C6F5)3 O
H
Et3SiH
H(Et3Si)2O
–B(C6F5)3
+ B(C6F5)3
Applications in Green Chemistry
Berkefeld, A.; Piers, W. E.; Parvez, M. JACS, 2010, 132 , 10660-10661.
Converting CO2 to Fuels
■ Addition of Et3SiH to CO2 in the presence of an FLP efficiently reduces CO2 to CH4
HB(C6F5)3NH2
MeMe
MeMe
Et3SiH + B(C6F5)3
HEt3Si B(C6F5)3
OO B(C6F5)3
HTMPH
CO2
OO SiEt3
H
OO SiEt3
Et3SiH
H
HEt3Si B(C6F5)3
HEt3Si B(C6F5)3 O
H
Et3SiH
H(Et3Si)2O
HEt3Si B(C6F5)3
(Et3Si)2O
HCH3
–B(C6F5)3
+ B(C6F5)3 + B(C6F5)3
Limitations and Future Directions
Sumerin, V.; Schulz, F.; Nieger, M.; Leskelä, M.; Repo, T.; Rieger, B. ACIE, 2008, 47, 6001-6003.
■ Currently cannot hydrogenate aldehydes or ketones catalytically
■ Discovery of better FLP catalysts for asymmetric induction; expanding the scope
■ Hydrogen gas storage - currently FLPs can achieve 0.25 wt % H2; whereas to be practicalneed 6 - 9 wt % H2 (i.e. ammonia-borane)
NH2 Me
MeMeMe
HB(C6F5)3
O
H
20 ºC, 1hr
OB(C6F5)3
NH2 Me
MeMeMe
95%
to olefin hydrogenations
Summary
■ I. Theories on the Mechanism of H2 Activation
■ Electron Transfer Model that Invokes Frontier Molecular Orbitals
■ Electric Field Model that disregards Frontier Molecular Orbitals
■ Secondary non-covalent interactions play key role in lowering H2 activation barrier
■ II. Applications of FLPs in Hydrogenation Reactions and Storage of Small Molecules
■ Catalytic hydrogenation of imines, enamines, nitriles, aziridines, silyl enol ethers,
■ Stoichiometric hydrogenations of aldehydes, ketones
■ Asymmetric imine hydrogenations
cyclic ethers, alkenes, alkynes, ynones
■ Advances in area of green chemistry