PinBIM and various boranes were investigated for their catalytic activity in CO2 reduction. Control experiments showed that pinacolborane could reduce CO2, which was unexpected. NMR analysis of reaction products identified a B-O-B species indicative of CO2 reduction. Ensuring properly air- and water-free conditions was challenging due to adventitious contamination in glassware. Future work will optimize conditions for CO2 reduction using PinBIM and fully characterize products like the B-O-B intermediate.

1. Determination of the Catalytic Activity of
Pin
BIM and Various Boranes for CO2
Reduction
Franklin Monzon
Junior Transfer Applicant
Figueroa Group - Summer 2015
4Cs at UCSD*
*An NSF-Funded REU Program

2. Project Goal
Catalytic CO2
reduction with Pin
BIM and pinacolborane
– Verify the chemistry
– Optimize the conditions
– Define future directions

3. Background: Lewis Acid-Base
Chemistry

Lewis acids and bases are chemicals characterized by their ability
to accept or donate electron pairs*
• Adducts form when they react.
Background: Lewis Acid-Base
Chemistry
*G.N. Lewis, Valence and the Structure of Atoms and Molecules, Chemical Catalogue Company, Inc., New York, 1923.
**Image, Silberberg, M. Chemistry. 5th ed. New York: Mcgraw-Hill Education, 2009, 817-818.

4. Frustrated Lewis Pairs: History

1942: Brown observed the following while testing the influence of
steric factors on bond strength
Brown, H.C.; Schlesinger, H.I. JACS, 1942, 64, 325-329.
Given that lutidine reacts with boron trifluoride,
trimethylborane would seem to form an adduct as well.
Adduct formation prevented by sterics
Frustrated Lewis Pairs: History

5. Frustrated Lewis Pairs: History

FLPs exist whenever Lewis acids and bases exist in the same
solution or on the same material and are uncoordinated due to
adverse steric conditions

Brown's work came before current FLP distinction
Brown, H.C.; Schlesinger, H.I. JACS, 1942, 64, 325-329.
Frustrated Lewis Pairs: History

6. Since then...
FLPs have found use in...
 Activation of H2

Catalysis of hydrogenations
– Of imines, nitriles, aziridines, ketimines, enamines,
anilines, olefins and alkynes
 Reversible binding of CO2
 Binding of SO2
and N2
O
 Reduction of CO2
to CH4

7. FLP Activation of H2
Welch, G. C.; San Juan, R.R.; Masuda, J. D.; Stephan, D. W. Science, 2006, 314, 1124-1126.
Reversible hydrogen
binding exhibited by
phosphine-borane
FLP

8. CO2
Reduction

Via intermolecular
FLP

Silane-borane
reductant mixture
Berkefeld, A.; Piers, W.E.; Parvez, M. JACS,
2010, 132, 10660-10661.

9. Value of CO2
Reduction
 CO2
has a significant impact on climate change
 Also, CO2
would be an effective C-1 source
CO2
mostly untapped carbon source...
Silberberg M. Chemistry. 5th ed. New York: Mcgraw-Hill Education, 2009, 258.
Value of CO2
Reduction

10. Frustrated Lewis Pairs:
Figueroa Group

FLPs synthesized using m-terphenyl iscyanides

Working toward FLP-based catalytically reducing materials
 Pin
BIM is an intramolecular
FLP due to its Lewis acidic
boron and Lewis basic
nitrogen**
Barnett, B.R.; Moore, C.E.; Rheingold, A.L.; Figueroa, J.S. Chem. Commun., 2015, 51, 541.

11. Pin
BH Rationale: Prevent Alkyl Migration
 Alkyl (or cyclohexyl) migration favors irreversible binding of CO2
 For example, Cy2
BIM irreversibly binds CO2
Barnett, B.R.; Moore, C.E.; Rheingold, A.L.; Figueroa, J.S. Chem. Commun., 2015, 51, 541.

12. Why Pinacolborane ?
 Pin
BIM doesn't exhibit alkyl migration
 But Pin
BH, less Lewis acidic than HB(Cy)2
, Pin
BIM not as reactive with CO2
Barnett, B.R.; Moore, C.E.; Rheingold, A.L.; Figueroa, J.S. Chem. Commun., 2015, 51, 541.

13. Pin
BIM: Synthesis
Barnett, B.R.; Moore, C.E.; Rheingold, A.L.; Figueroa, J.S. Chem. Commun., 2015, 51, 541.
Pin
BIM synthesis carried out as follows

14. Can Pin
BIM Catalyze CO2
Reduction,
using Pin
BH ?

Catalytic-style experiment was devised with pinacolborane
(Pin
BH) as the reductant.

NMR results demonstrated that reactions occurred but results
varied over experiments of even the same type
Barnett, B.R.; Moore, C.E.; Rheingold, A.L.; Figueroa, J.S. Chem. Commun., 2015, 51, 541.

15. Pin
BIM Catalytic Experiments
Catalysis Results: B-O-B Species Among other products
 In the literature, B-O-B taken to be indicative of CO2
reduction

Proposed intermediate, still to be characterized
Experiments based on Barnett, B.R.; Moore, C.E.; Rheingold, A.L.; Figueroa, J.S. Chem. Commun., 2015, 51, 541.

16. Control Experiments: Pin
BH + CO2
 Essential to determine if Pin
BH is reducing CO2

A set of control reactions run
• Surprising if possible without a catalyst
Experiments based on Barnett, B.R.; Moore, C.E.; Rheingold, A.L.; Figueroa, J.S. Chem. Commun., 2015, 51, 541.

17. Control Experiments: Pin
BH + H2
O

Is there water in the reaction?
– Performed a control experiment where water was added.
– Results similar, B-O-B ester produced among trace products
Experiments based on Barnett, B.R.; Moore, C.E.; Rheingold, A.L.; Figueroa, J.S. Chem. Commun., 2015, 51, 541.

18. Control Experiments: Results

NMR spectroscopy determined that pinacolborane appeared to
react with CO2

Which is highly unexpected, demonstrating a need to ensure
totally air- and water-free conditions.

X-ray crystallography would help characterize products.
Experiments based on Barnett, B.R.; Moore, C.E.; Rheingold, A.L.; Figueroa, J.S. Chem. Commun., 2015, 51, 541.

19. Ensuring Properly Controlled
Conditions
 All experiments assembled in a glove-box under atmosphere of N2

Gas additions performed using a Schlenk line as shown below

20. Ensuring Properly Controlled
Conditions

Drierite drying column used
 Drierite is anhydrous CaSO4
 Expected “dry” CO2
and H2

21. Adventitious Water

While distilling benzophenone-treated benzene, noticed...
– The sample of benzene appeared to turn a lighter blue under
dynamic vacuum while on the Schlenck line.
– Inferred water was present in the line.

22. Adventitious Water

Set up two control experiments
– 3-mL benzene, 15 drops benzophenone indicator under
constant stirring in a 50-mL Schlenk ampoule.
– Both turned yellow indicating presence of water

23. Results

Synthesized Pin
BIM according to Barnett's prep

Established some standard conditions for BIM reactions

Demonstrated that Pin
BIM is more water- and/or air-sensitive
than expected

Determined the Schlenk line was contaminated

Outlined some possible products of the catalytic reaction

B-O-B species

Dipp-aniline species

Diborane species

24. Future Goals of the Project
 Determine whether pinacolborane is exhibiting CO2
reduction
 Optimize conditions for CO2
reduction with Pin
BIM

Ensure air-free, water-free work

Complete testing on the available boranes.
 Work toward a BIM capable of catalytic H2
activation and CO2
reduction, for use in future work

25. Lessons Learned

Test your assumptions (e.g., sensitivity of the chemistry)

Follow established preps

Good technique is always a good idea

Be flexible and prepared to learn

26. Special thanks to
Dr. Josh Figueroa, Dr. Stacey Brydges, Dr. Haim Weizman;
Kyle Mandla, Brandon Barnett, Noah Mendelson
and Charles Mokhtarzadeh of Figueroa Group

27. Thank You UCSDThank You UCSD

28. References
[1] G.N. Lewis, Valence and the Structure of Atoms and Molecules,
Chemical Catalogue Company, Inc., New York, 1923.
[2] Silberberg, M. Chemistry. 5th ed. New York: Mcgraw-Hill
Education, 2009, 817-818.
[3] Welch, G. C.; San Juan, R.R.; Masuda, J. D.; Stephan, D. W.
Science, 2006, 314, 1124-1126.
[4] Chen, D.; Wang, Y.; Klankermeyer, J. ACIE, 2010, 49, 9475-9578.
[5] Chase, P.A.; Welch, C.; Jurca, T.; Stephan, D.W. ACIE, 2007, 46,
8050-8053.
[6] Chase, P.A.; Jurca, T.; Stephan, D.W. Chem. Comm., 2008,
1701-1703.
[7] Spies, P.; Schwendemann, S.; Lange, S.; Kehr, G.; Frohlich, R.;
Erker, G. ACIE, 2008, 47, 7543-7546.
[8] Wang, H.; Frohlich, R.; Kehr, G.; Erker, G. Chem. Comm., 2008,
5966-5968.
[9] Webb, J.D.; Laberge, V.S.; Geier, S.J.; Stephan, D.W.; Crudden,
C.M. Chem. Eur. J., 2010, 16, 4895-4902.
[10] Geier, S.J.; Chase, P.A.; Stephan, D. W. Chem. Comm., 2010,
46, 4884-4886.
[11] Mahdi, T.; Heiden, Z.M.; Grimme, S.; Stephan, D. W. JACS,
2012, 134, 4088-4091.
[12] Greb, L.;Ona-Burgos, P.; Schirmer, B.; Grimme, S.; Stephan,
D.W.; Paradies, J. ACIE, 2012, 51, 10164-10168.
[13] Chernichenko, K.; Madarasz, A.; Papai, I.; Nieger, M.; Leskela,
M.; Repo, T. Nat. Chem. 2013, 5, 718-723.
[14] Momming, C.M.; Otten, E.; Kehr, G.; Frohlich,R.; Grimme, S.;
Stephan, D.W.; Erker, G. ACIE, 2009, 48, 6643-6646.
[15] Sajid, M. et al. Chem. Sci., 2013, 4, 213-219.
[16] Otten, E.; Neu, R.C.;Stephan, D.W. JACS, 2009, 131, 9918-
9919.
[17] Berkefeld, A.; Piers, W.E.; Parvez, M. JACS, 2010, 132, 10660-
10661.
[18] Barnett, B.R.; Moore, C.E.; Rheingold, A.L.; Figueroa, J.S. Inorg.
Chem., 2009, 48, 8362.
[19] Barnett, B.R.; Moore, C.E.; Rheingold, A.L.; Figueroa, J.S.
Chem. Commun., 2015, 51, 541.