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