the activation of carbon dioxide with molybenum and iron complexes by alex dale macintosh bs

172 Pages·2015·6.83 MB·English

CARBON DIOXIDE AS A C SOURCE:
1
THE ACTIVATION OF CARBON DIOXIDE WITH
MOLYBENUM AND IRON COMPLEXES

BY
ALEX DALE MACINTOSH
B.S., WAKE FOREST UNIVERSITY, 2010
M.A., CHEMISTRY, BROWN UNIVERSITY, 2012

A DISSERTATION SUBMITTED IN PARTIAL FULLFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
IN THE DEPARTMENT OF CHEMISTRY AT BROWN UNIVERSITY

PROVIDENCE, RHODE ISLAND
MAY 2015
© Copyright 2015 by Alex Dale MacIntosh
This dissertation by Alex D. MacIntosh is accepted in its present form
by the Department of Chemistry as satisfying the
dissertation requirement for the degree of Doctor of Philosophy.

Date__________ _________________________________
Wesley H. Bernskoetter, Advisor

Recommend to the Graduate Council

Date__________ _________________________________
Eunsuk Kim, Reader

Date__________ _________________________________
Paul G. Williard, Reader

Approved by the Graduate Council

Date__________ _________________________________
Peter M. Weber, Dean of the Graduate School

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Vita
Alex Dale MacIntosh was born on November 20, 1987, in Mount Holly, North
Carolina. He is the son of Keith and Cindi MacIntosh, brother to Brian MacIntosh, and
uncle to Logan and Isabella. Alex graduated from East Gaston High School in 2006 and
began studying at Wake Forest University in Winston-Salem, North Carolina. In May
2010, he graduated Cum Laude with a Bachelor of Science in Chemistry (with a
concentration in materials chemistry).
Alex began his chemistry career at Wake Forest in the laboratory of Professor
Ronald E. Noftle. Under Prof. Noftle’s supervision, he worked on the synthesis and
characterization of novel thiophene-derived ligands for the construction of metal-organic
frameworks. While at Wake Forest, Alex was the recipient of the Merck Index Award in
Chemistry, which is presented to an outstanding chemistry major of the senior class.
In order to continue his research career in chemistry, Alex entered the doctoral
program at to Brown University in the fall of 2010 and began research under the tutelage
of Professor Dwight A. Sweigart. After the passing of Professor Sweigart in the fall of
2012, Alex worked under the mentorship of Professor Wesley H. Bernskoetter for the
remainder of his graduate school career.
On July 5, 2013, Alex asked Emily Elizabeth Russo, a doctoral candidate in
Egyptology at Brown University, to marry him. She said “yes,” and the wedding is
scheduled to take place in Morristown, New Jersey, on May 16, 2015.
Alex, with his Ph.D. completed, looks forward to starting a new career and life in
Rhode Island with his soon-to-be wife.

iv
Acknowledgements
Brown University has been my home for the last five years. Over the course of my
tenure at Brown I have created many relationships, professional and personal, across the
campus and the world. It is because of these people that I have succeeded in my journey
to obtain my Ph.D., and it is because of their presence that my stay has been both
memorable and enjoyable.
First and foremost, I must acknowledge Professor Dwight Sweigart (a.k.a. boss). I
am privileged that I was able to spend the last two years of his life as his mentee and his
final graduate student in a long line of successful and talented chemists. He accepted me
into his group with great enthusiasm and helped me begin my Ph.D. journey. He was
always known for his great love and dedication to his students, as well as being the life of
the party. He was also notorious for taking us out of the lab and onto the golf course on
beautiful days. His passing was a great loss, and he is sorely missed.
I would like to thank Professor Wesley Bernskoetter for accepting me into his group
and for all of the mentorship and guidance he has provided. Wes has helped me learn more
about organometallic chemistry than I thought possible. Many days were spent in chatting
and laughing in the group office and munching on snacks that were always available. I
could never ask for a better teacher and mentor, and I am very proud to be his second Ph.D.
recipient. I know he will continue producing great chemists and high quality research.
Special thanks to a great teacher, an amazing person, and an excellent friend, Dr.
Brian Hanna. Brian helped me immensely with my transition to the Bernskoetter group
and taught me many of the air-free techniques required for research in organometallic
chemistry. Together we were able to get some great results and have some fun on the side.
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I have been fortunate to work alongside some great chemists and amazing people
in the Sweigart and Bernskoetter groups. Wei and Huan from the Sweigart group were
very helpful and always a great source for information. Hongwei, Yuanyuan, Brian, and
Dong accepted me ardently as a member of the Bernskoetter group and were all
instrumental in my transition. Yuanyuan is an extremely talented chemist, and we have
produced some remarkable results together. Liz and Ryan were amazing additions to the
Bernskoetter group and have been a great pleasure to work alongside. I wish you both the
best of luck in obtaining your Ph.D.’s. I was lucky to work with several undergraduates in
the laboratory throughout my stay. Thanks for good times Ariana, Zoe, and Evan.
Thank you to Steven Ahn for everything. You are a true friend and colleague. We
were able to do some great electrochemical work that provided much needed insight. I
know that I will continue to use your vast electrochemistry knowledge in the next stage of
my career.
The Chemistry Department at Brown University is full of amazing staff and faculty.
Thank you Professor Kim, Professor Williard and Professor Hess. Also many thanks to
Rose, Sheila, Eric, Lynn, Al, and Allen. You have all had a major impact on my career at
Brown.
Thank you to all of my family for the encouragement and support throughout the
years. Dad, you are not only my father, but also my best friend and an integral part of my
graduate school journey. Mom, you have always pushed me to reach my full potential with
love and support. Brian, I could never ask for a better brother and friend and look up to
you with great respect. I also wish to thank my grandparents for all of their love and
support. Unfortunately, Frank MacIntosh (Pappy) is no longer with us, but I know he
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would be very proud that another Dr. MacIntosh has come about for the first time in four
generations. It is rare to have the family support I’ve had, and for that I am eternally
grateful.
There is still one person I have yet to mention. Though last on the list, she is the
most important person in my life. My final acknowledgment is Emily, my fiancée. Words
cannot describe how great of a person she is and how much she means to me. Thank you
for your constant love, support, and guidance throughout the years. You’ve seen me at my
best and worst and everything in between, yet are still with me. I am looking forward to
May 16 of this year when I can finally call you my wife and we can begin the next stage
of our life.
Cheers!

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Abstract
The current reliance on finite fossil fuels for the production of commodity
chemicals has been recognized as unsustainable, and therefore has led to increasing
pressure for scientists to curb carbon dioxide (CO ) emissions and develop efficient CO
2 2
capture and utilization systems. One such system aimed toward the utilization of CO , as
2
well as decreasing dependence on fossil fuels, is using CO as a feedstock for fuels and
2
commodity chemicals. CO has enormous potential as an abundant, cheap, and safe C
2 1
source, but it is underutilized due to the harsh and difficult conditions normally required to
activate it. To circumvent this, high-energy starting materials can be used, which exhibit
high reactivity under mild conditions. Specifically, we are interested in the coupling of
CO with ethylene to produce acrylic acid and the hydrogenation of CO to produce formic
2 2
acid.
A series of zerovalent molybdenum complexes bearing triphosphine ligands,
[Ar PCH CH ] PPh, were synthesized and found to couple CO and ethylene, forming
2 2 2 2 2
isolable molybdenum(II) acrylate hydride species. Kinetic analysis of acrylate formation
revealed a first-order dependence on molybdenum, but no influence from CO pressure.
2
Comparison of steric and electronic features of the triphosphine ligands showed a strong
influence of ligand size on rate, with [(3,5-tBu-C H ) PCH CH ] PPh, coupling four times
6 3 2 2 2 2
slower than [(3,5-Me-C H ) PCH CH ] PPh. Additionally, a milder electronic effect was
6 3 2 2 2 2
observed for the complexes, with [(4-F-C H ) PCH CH ] PPh reducing CO at half the
6 4 2 2 2 2 2
rate of [Ph PCH CH ] PPh.
2 2 2 2
A pair of pincer-supported iron(II) carbonyl hydride complexes were found to
catalyze the hydrogenation of CO to formate in the presence of a Brønsted base. A
2
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remarkable enhancement in catalytic activity was observed upon addition of a Lewis acid
co-catalyst, where mechanistic investigation indicate that it destabilizes the resting state of
catalysis, aiding in formate extrusion. From these mechanistic insights, a new class of iron
catalysts based on an N-methylated PNMeP ligand were synthesized, and their activity for
CO hydrogenation was examined. Using this new class of iron catalysts, turnover
2
numbers near 60,000 were achieved for formate production, the highest activity reported
for an earth abundant system to date.

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Table of Contents
Vita ............................................................................................................................... iv
Acknowledgements ..............................................................................................................v
Abstract ............................................................................................................................ viii
Chapter 1 An Introduction ..................................................................................................1
Section 1.1 Carbon Dioxide as a C Source ............................................................2
1
Section 1.2 Formic Acid ..........................................................................................4
Section 1.3 Acrylic Acid .........................................................................................9
Section 1.4 References ..........................................................................................14
Chapter 2 Ancillary Ligand Effects on Carbon Dioxide-Ethylene Coupling at Zerovalent
Molybdenum ......................................................................................................................19
Section 2.1 Introduction .......................................................................................20
Section 2.2 Results and Discussion .......................................................................24
Section 2.3 Concluding Remarks ..........................................................................37
Section 2.4 Experimental.......................................................................................39
Section 2.5 References ..........................................................................................53
Chapter 3 Lewis-Acid Assisted Carbon Dioxide Hydrogenation Using a Pincer-
Supported Iron Catalyst .....................................................................................................56
Section 3.1 Introduction .......................................................................................57
Section 3.2 Results and Discussion .......................................................................62
Section 3.3 Concluding Remarks ..........................................................................81
Section 3.4 Experimental.......................................................................................84
Section 3.5 References ..........................................................................................90
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