Capture and Structural Determination
of Activated Intermediates in
Transition Metal Catalyzed CO2
Reduction Using CIVP Spectroscopy
Stephanie Craig
Johnson Lab
International Symposium on Molecular Spectroscopy
June 22, 2015
Capturing Short-Lived Intermediates
with Cryogenic Gas Phase Techniques
• Extreme sensitivity to study intermediates at low
concentrations
• Cryogenic cooling freezes intermediates into local minima
• Vibrational spectroscopy allows for structural
characterization of mass selected species
+
+
+
OH
N
Ir3+
NaIO4
N
Ir3+
O
or
N
O
Ir3+OH
O
possible first oxidation
products
water oxidation
catalyst precursor
onto water
oxidation
second oxidation
product
proposed resting state
Ingram, A. J. et. al. Inorg. Chem. 53 (2014)
Features of an Activated CO2
𝐶𝑂2 + 6𝐻+ + 6𝑒 − → 𝐶𝐻3 𝑂𝐻 + 𝐻2 𝑂
𝐶𝑂2 + 𝑒 − → 𝐶𝑂2· −
𝐶𝑂2· − + 6𝐻+ + 5𝑒 − → 𝐶𝐻3 𝑂𝐻 + 𝐻2 𝑂
ν3 CO2· –
1660 cm-1
689 cm-1
ν3 CO2
2349 cm-1
(CO2)7–
Predissociation Yield (a.u.)
Activating CO2 involves adding some electron
density into the π* antibonding orbital
THIS STEP IS
IMPORTANT
1000
1500
2000
2500
300
Photon Energy (cm-1)
C
2O
B. M. Mahan & R. J. Myers, University Chemistry (1987)
Kamrath, M. Z. et. al. J. Am. Chem. Soc. 132 (2010)
Features of an Activated CO2
The CO2 molecule will exhibit a bend in
order to compensate for the extra
electron density added
Expect this bend between neutral CO2
(180°) and CO2· – (133°)
C
133°
2O
B. M. Mahan & R. J. Myers, University Chemistry (1987)
Finding a CO2 Reduction Catalyst
NiII
H
NiI
H
Extra
d
Ni(cyclam)2+ - A well-studied
electron
I
Reduce
to Ni for CO2 reduction that
catalyst
necessary to
bind CO2
can be readily maded
x2-y2
dx -y
N
N
2
2
Ni2+
dz
z2
2
N
N
H
dxy
dxz
H
dxy
dxz
dyz
H
Electrochemistry
is first used to
reduce the stable
NiII compound to
the active NiI
catalyst
N
N
+H +
H
Ni
H
dyz
O
2+
H
III N
2+
+ CO 2
N
H
H
N
N
H
O
Ni
H
III N
N
H
H
N
N
H
Ni
I
H
+
N
N
O
N
N
reduction
H
H
N
N
H
H
Ni
II
N
N
+
H
+ CO 2
H
O
H
Ni
n
+ solvent
H
O
OH
H
H
N
N
N
N
H
H
2+
Ni
S
2+
III N
N
H
CO mechanism
e
-
OH -, CO
H
Formate mechanism
e
-
HCO 2
-
Morris, A. J. et. al. Acc. Chem. Res. 42 (2009)
Experimental Setup
Temperature Controlled
Ion Trap
Mounted to He Cryostat
Temperature Controlled
Helium Cryostat
4 to 300 K Ion
Wiley-
DC-Turning
DC-Turning
Quad
Quad
McLaren
TOF
Reflectron
Optics
Reflectron
Ion Optics
2m Flight Tube
2m Flight Tube
Differential
Aperture
Aperture
RF-Ion
Guides
RF-Ion
Wiley McLaren
Extraction
Nd:YAG
OPO/OPA
Nd:YAG
Tunable IR
600-4500 cm-1
Guides
Skimmer
Skimmers
ESI
Needle
ESI
Needle
Heated
Capillary
2mM [EMIM][I]
in H2O/MeCN
MCP
Detector
LaserVision
OPO/OPA
Tunable IR
600-4500 cm-1
Det
A (Likely Unsuccessful) Look Into
Ni(cyclam)2+
Ion Signal (a.u.)
0
Ni(cyclam)2+·(CO2)n
1
2
3
4 n
140
160
180
200
m/z
Only get NiII species
220
A (Likely Unsuccessful) Look Into
Ni(cyclam)2+
ν1 – symmetric
stretch
ν3 – asymmetric
stretch
Calc. Intensity CO2 Pred. Yield (a.u.)
ν2 - bend
neutral CO2
asym stretch
νNH
ν3
2ν2 + ν3
νCH
ν 1 + ν3
Ni(cyclam)2+ does
NOT activate CO2
2000
2400
2800
3200
Photon Energy (cm-1)
3600
BP86/tzvp
Where to Get a Stable NiI Species?
• So not any old Ni catalyst will reduce CO2
– Need to find a stable NiI catalyst
– It turns out we have one!
N
N
Ni+
N
N
[Ni(bipyridine-(N2Me)2)]+ = Ni(L-N4Me2)+
Ni(L-N4Me2)+ - Getting to the Active
Species
2+
N
N
N
Ni+
N
N
Ni+
N
N
N
collisional
activation
N
N
Ni+
N
N
[Ni(bipyridine-(N2Me)2)]2(diphenyldiacetylene)2+
[Ni(bipyridine-(N2Me)2)]+
BP86/tzvp
Ni(L-N4Me2)+ - Getting to the Active
Species
[NiI-L
[Ni(I)-L(N4Me2)(C16H10)]+
(N4Me2)]+
N
N
Ni+
N
N
[Ni(I)-L(N4Me2)]+
[Ni(II)-L(N4Me2)F]+
[Ni(I)-L(N4Me2)O2]+
326
320
340
360
380
400
327
420
440
m/z
m/z
460
328
480
329
500
Left with a stable NiI
species
520
540
560
[Ni(bipyridine-(N2Me)2)]+
BP86/tzvp
+CO2
m/z
Only able to tag one CO2
molecule
ν3
νCH
Predissociation Yield (a.u.)
320 330 340 350 360 370 380
νNH
2ν2 + ν3
νCH
ν1 + ν3
Ni(cyclam)2+·CO2
NiI(L-N4Me2)
neutral CO2
asym stretch
Ni(L-N4Me2 ) +·CO2
Ion Signal (a.u.)
Ni(L-N4Me2)+ - Can This NiI Compound
Activate CO2?
What is this peak
at 1921 cm-1?
1000 1500
2000
2500
3000
3500
Photon Energy (cm-1)
BP86/tzvp
Isotopic Substitution To Verify Band
Shifts Due to CO2
νCH
ν1 + ν3
+CO2
NiI(L-N4Me2)
+O2
NiI(L-N4Me2)
+13CO2
320
330
340
350
360
370
380
Predissociation Yield (a.u.)
Ion Signal (a.u.)
2ν3
50 cm-1
2ν3
ν3 = ν13CO asym
νCH
m/z
Have a shift of the peak at
1921 cm-1 – It is the
asymmetric CO2 stretch!
1500
2000
2500
3000
Photon Energy (cm-1)
3500
Ni(L-N4Me2)+·12CO2 Ni(L-N4Me2)+·13CO2
ν3
Isotopic Substitution To Verify Band
Shifts Due to CO2
νCH
ν1 + ν 3
ν1 + ν3
ν1 should appear at 1128
cm-1, almost 200 cm-1 red
of the neutral CO2
symmetric stretch
2ν3
Predissociation Yield (a.u.)
The difference spectrum
also highlights the
separation of the ν1 + ν3
(†) combination band
from the CH stretches
Expect to see the
isotopically labeled
combination band in oval
50 cm-1
2ν3
ν3 = ν13CO asym
νCH
1500
2000
2500
†
3000
Photon Energy (cm-1)
3500
Ni(L-N4Me2)+·12CO2 Ni(L-N4Me2)+·13CO2 Subtraction
ν3
Is This Red Shifted CO2 Activated?
νCH
ν3
Predissociation Yield / Calculated
Intensity
Ni(L-N4Me2 ) +·CO2
Checklist: 1. Position of ν3
2. A nonlinear CO2
1000 1500
2000
2500
3000
3500
Photon Energy (cm-1)
Is This Red Shifted CO2 Activated?
νCH
Ni(L-N4Me2 ) +·CO2
Checklist:  Position of ν3
2. A nonlinear CO2
Activated CO2 asymmetric
transition appears between
that of the neutral and
radical anion CO2
ν3 CO2
ν3 free
CO2
–
1000 1500
(CO2) 7–
Predissociation Yield / Calculated
Intensity
ν3
2000
2500
3000
3500
Photon Energy (cm-1)
Kamrath, M. Z. et. al. J. Am. Chem. Soc. 132 (2010)
Is This Red Shifted CO2 Activated?
νCH
Ni(L-N4Me2 ) +·CO2
Checklist:  Position of ν3
 A nonlinear CO2
Activated CO2 asymmetric
transition appears between
that of the neutral and
radical anion CO2
148°
ν3 CO2
ν3 free
CO2
–
1000 1500
(CO2) 7–
Predissociation Yield / Calculated
Intensity
ν3
2000
2500
3000
3500
Photon Energy (cm-1)
BP86/tzvp
Kamrath, M. Z. et. al. J. Am. Chem. Soc. 132 (2010)
Is This Red Shifted CO2 Activated?
νCH
ν3
ν3 CO2
ν3 free
CO2
–
1000 1500
(CO2) 7–
Predissociation Yield / Calculated
Intensity
Activated CO2 asymmetric
transition appears between
that of the neutral and
radical anion CO2
148°
Ni(L-N4Me2 ) +·CO2
WE ACTIVATED CO2!
2000
2500
3000
3500
Photon Energy (cm-1)
BP86/tzvp
Kamrath, M. Z. et. al. J. Am. Chem. Soc. 132 (2010)
A Closer Look at the Activated CO2
νCH
ν3
148°
ν3 CO2
ν3 free
CO2
–
1000 1500
(CO2) 7–
Predissociation Yield / Calculated
Intensity
Increase intensity in the
methyl CH stretches from
interaction with the CO2
Ni(L-N4Me2 ) +·CO2
WE ACTIVATED CO2!
2000
2500
3000
3500
Photon Energy (cm-1)
BP86/tzvp
Kamrath, M. Z. et. al. J. Am. Chem. Soc. 132 (2010)
Acknowledgements
•
•
•
•
•
•
•
•
•
•
•
Prof. Mark Johnson
Prof. Gary Weddle
Dr. Fabian Menges
Dr. Joe DePalma
Joe Fournier
Conrad Wolke
Olga Gorlova
Patrick Kelleher
Niklas Tötsch
Joanna Denton
Chinh Duong
SECRET SLIDES
We Activated CO2! What Do We Do Next?
νCH
ν3
148°
ν3 CO2
ν3 free
CO2
–
1000 1500
(CO2) 7–
Predissociation Yield / Calculated
Intensity
𝐶𝑂2· − + 6𝐻+ + 5𝑒 − → 𝐶𝐻3 𝑂𝐻 + 𝐻2 𝑂
Ni(L-N4Me2 ) +·CO2
Introduce acids to get protons
on the activated CO2
2000
2500
3000
3500
Photon Energy (cm-1)
BP86/tzvp
Kamrath, M. Z. et. al. J. Am. Chem. Soc. 132 (2010)
We Activated CO2! What Do We Do Next?
νCH
ν3
ν3 CO2
ν3 free
CO2
–
(CO2) 7–
Predissociation Yield / Calculated
Intensity
Ni(L-N4Me2 ) +·CO2
Introduce acids to get protons
on the activated CO2
1000 1500
2000
2500
3000
3500
Photon Energy (cm-1)
BP86/tzvp
Kamrath, M. Z. et. al. J. Am. Chem. Soc. 132 (2010)
We Activated CO2! What Do We Do Next?
Introduce acids to get protons
on the activated CO2
0
500
1000
1500
2000
Photon Energy (cm-1)
2500
3000
3500
BP86/tzvp
Ni(cyclam)2+ - A Look at the Ligand
The cyclam ligand has five possible conformational isomers
Only the trans-I and trans-III ligands exist in solution – what about gas
phase?
trans-I
trans-II
trans-III
Ligand
Isomer
DFT (S-VWN5)1
(kJ/mol)
trans-I
0.98
trans-II
10.16
trans-III
0.00
trans-IV
59.23
trans-V
24.64
kT = 2.5 kJ/mol @ 300K
trans-IV
trans-V
1. Adam, K. R. et. al. Inorg. Chem. 36 (1997)
2+ - A Look at the Ligand
Ni(cyclam)
ν
CH
Only the trans-III
isomer present in
the gas phase!
Pred. Yield (a.u.)
νNH
νCH
Trans III
νNH-degen
trans-III
Calculated Intensity
νNH-degen
trans-I I
Trans
νNHβ
1000 1200 1400 1600
2800
νNHβ
3000
νNHα
νNHα
3200
Photon Energy (cm-1)
β
3400
α
3600
BP86/tzvp
Transitioning From CO2 to CO2· –
νCN
1000
1500
(CO2)7–
ν3 CO2–
2000
Photon Energy (cm-1)
Py-CO2 –·(CO2)3
Ni(L-N4Me2)+·CO2
Predissociation Yield (a.u.)
148°
Ni(cyclam)2+·CO2
neutral CO2
asym stretch
ν3 CO2
ν3 (cm-1)
θOCO
RCO (Å)
CO2
2349
180°
1.162
Ni(L-N4Me2)+·CO2
1921
148°
1.231
Py-CO2 –·(CO2)3
1705
133°1
1.2401
CO2 · –
1660
134°2
1.432
The activated CO2 appears to be
an intermediate step in the
transition between neutral and
negatively charged CO2
2500
3000
3500
1. Kamrath, M. Z. et. al. J. Am. Chem. Soc. 132 (2010)
2. Almlöf, J. et. al. Chem. Phys. Lett. 28 (1974)
Ni(cyclam)2+ and Formate
νCO asym
O
νCO sym
νCH
H
O
H
O
O
H
H
O
H
O
N
H
O
N
Ni
N
H
H
N
H
H
N
H
N
Ni
N
H
N
H
1200
1400
1600
1800
2000
2200
2400
2600
Photon Energy
(cm-1)
2800
3000
3200
3400
3600
3800
Ni(cyclam)2+ and Formate
H
Ni(Cyc)2+•D
H
N
2
νNH
N
Ni2+
N
N
H
νCOs
H
νCOa
νfree
NiCyc(formate)+•D2
NiCyc(d-formate)+•D2
CH wag
CH stretch
Difference
800 1000 1200 1400 1600 1800 2000 2200
Photon Energy (cm-1)
2750
3000
3250
3500
Ni(cyclam)2+ with Stuff
H
N
H
N
Ni
N
N
H
H
H
C
O
O
H
H
N
Ni
N
II
N
N
H
H
Na+
H
N
H
N
Ni
O
N
H
N
O
O
O
H
H
H
800
1000
N
H
N
Ni
O
1200
O
H
N
O
1400
H
N
N
O
Ni
N
1600
1800
2200
27502000 3000
3250
3500
N
H
N
H
H
H
N
H
N
Ni
O
N
C
H
N
O
H
1000
1200
1400
1600
2800
3000
Photon Energy, cm
-1
3200
3400
3600
How Important are the NH Groups?
Ni(cyclam)2+·(CO2)n
H
H
N
N
Kubiak and co-workers have noted that by
methylating the NH groups the efficiency of the
reduction reduces from 90% to 20%1 - will it effect the
CIVP spectra?
Ni2+
0
H
1 2
23
4
N
H
Ni(DMC)2+·(CO2)n
n
Ion Signal (a.u.)
N
01
120
140
160
180
200
Ni(DMC)2+ is
significantly
harder to tag with
CO2 than
Ni(cyclam)2+ seems as though
CO2 binds to the
NH groups
220
m/z
1. Froehlich, J. D. et. al. Inorg Chem. 51 (2012)
How Important are the NH Groups?
νNH
H
N
Predissociation Yield (a.u.)
Ni2+
N
Splitting of the NH peak observed for Ni(DMC)2+
 splitting the degeneracy of the amine group
H
Calculations confirm position of
N
CO2 attachment
2ν2 + ν3
N
H
H
ν1 + ν3
Ni(cyclam)2+
H
H3C
N
N
Ni2+
Splitting of NH
N
H
3000
3200
N
Ni(DMC)2+
CH3
3400
3600
3800
Photon Energy (cm-1)
BP86/tzvp
What If We Pull on the NH Groups?
Take a look at acidity of NH groups by
pulling on the protons with different
conjugate bases
Increasing Deprotonation
NH stretch
Increase in CH
stretches not intrinsic
to formate – lose CH
stretch when formate
is duterated
Ni(cyclam)2+
Ni(cyclam)(PF6)+
Ni(cyclam)(formate)+
Ni(cyclam)(d-formate)+
2800 2900 3000 3100 3200 3300 3400
Photon Energy (cm-1)
Decreasing pKb
Red shift of NH
transition and
increased intensity in
CH stretches
Predissociation Yield / Calculated
Intenisty
CH stretches
326
327
328
m/z
329
Two Nickel Based Catalysts
Ni(cyclam)2+
• A well-studied and highly
efficient NiII catalyst for
CO2 reduction
• Electrochemistry is used
to first reduce the metal
center to NiI
H
Ni(L-N4Me2)+
• A novel NiI species not yet
studied as a catalyst for
the reduction of CO2
– several bipyridine catalysts
do exist though
H
N
N
N
Ni2+
N
N
Ni+
N
N
H
H
N
+CO2
320 330 340 350 360 370 380
m/z
Only able to tag one CO2
molecule
νCH
ν3
434 cm-1
νCH
ν3 free
CO2
ν3 CO2–
1000 1500
2ν2 + ν3
2000
2500
ν1 + ν3
(CO2) 7-
Is this really an
activated CO2?
ν3
Predissociation Yield / Calculated
Intensity
NiI(L-N4Me2)
νNH
Ni(cyclam)2+·CO2
148°
neutral CO2
asym stretch
Ni(L-N4Me2 ) +·CO2
Ion Signal (a.u.)
Ni(L-N4Me2)+ - Can This NiI Compound
Activate CO2?
3000
3500
Photon Energy (cm-1)
BP86/tzvp
Kamrath, M. Z. et. al. J. Am. Chem. Soc. 132 (2010)
Did We Miss Something In The
Mechanism?
H
+H
N
N
+
H
Ni
H
O
2+
H
III N
2+
+ CO 2
N
H
H
N
N
H
O
Ni
H
III N
N
H
H
N
N
H
Ni
I
H
+
N
N
+ CO 2
H
H
H
H
H
H
O
N
N
reduction
N
N
O
H
Ni
II
N
N
+
Ni
n
+ solvent
H
O
OH
H
H
N
N
N
N
H
H
2+
Ni
S
2+
III N
N
H
CO mechanism
e
-
OH -, CO
H
Formate mechanism
e
-
HCO 2
-
Nominally use electrochemistry to reduce
Ni center – NiI the active species
Morris, A. J. et. al. Acc. Chem. Res. 42 (2009)
Future Work
• Now that we have an activated CO2, what kind
of chemistry can we do with it?
– Build a liquid nitrogen octopole guide to cool and
tag CO2 to Ni(L-N4Me2)+ before entering the trap
– Introduce small molecules (like H2, NO, BPh3)
through the pulsed valve into the trap to form
intermediates in the catalytic cycle or look at the
ability to deprotonate a Lewis acid
– Attach water(s) to the activated CO2 to look at the
effects of charge transfer
andLaserVision
stabilization
Nd:YAG
Temperature Controlled
Ion Trap
Mounted to He Cryostat
Temperature Controlled
Helium Cryostat
4 to 300 K Ion
Wiley-
DC-Turning
DC-Turning
Quad
Quad
McLaren
TOF
Reflectron
Optics
Reflectron
Ion Optics
2m Flight Tube
2m Flight Tube
Differential
Aperture
Aperture
RF-Ion
Guides
RF-Ion
Wiley McLaren
Extraction
Nd:YAG
MCP
Detector
OPO/OPA
Guides
Tunable IR
600-4500 cm-1
Skimmer
OPO/OPA
Skimmers
ESI
Needle
ESI
Needle
Heated
Capillary
2mM [EMIM][I]
in H2O/MeCN
Tunable IR
600-4500 cm-1
Detector
Can Isolated Ni(cyclam)2+ Activate CO2?
H
+H
H
N
N
H
+
H
Ni
I
H
III N
Ni
N
H
H
+ CO 2
H
H
N
N
+
N
N
O
O
H
H
H
H
H
N
N
N
Ni II N
H
H
2+
+ CO 2
O
N
N
reduction
2+
H
+
Ni
n
+ solvent
H
O
H
N
N
N
N i III
N
H
H
O
OH
H
H
N
N
N
N
H
H
2+
Ni
S
2+
III N
N
H
CO mechanism
e
-
OH -, CO
Formate mechanism
e
-
HCO 2
-
Morris, A. J. et. al. Acc. Chem. Res. 42 (2009)
Cryogenic Ion Vibrational Predissociation (CIVP)
Spectroscopy
A+· Tagm + hn → A+ · Tagn + (m-n) Tag
Generate
Ions
Isolate
One Mass
Excite
With Laser
a)
Second
Mass Spec
b)
hn
mass
SarGlyH+•He
Predissociation Yield
photofragments
kIVR
d)
mass
c)
kevap
3300 3350 3400 3450 3500 3550 3600 3650
Photon Energy (cm-1)
mass
Experimental Setup
Temperature Controlled
Ion Trap
Mounted to He Cryostat
Temperature Controlled
Helium Cryostat
4 to 300 K Ion
Wiley-
DC-Turning
DC-Turning
Quad
Quad
McLaren
TOF
Reflectron
Optics
Reflectron
Ion Optics
2m Flight Tube
2m Flight Tube
Differential
Aperture
Aperture
RF-Ion
Guides
RF-Ion
Wiley McLaren
Extraction
Nd:YAG
OPO/OPA
Nd:YAG
Tunable IR
600-4500 cm-1
Guides
Skimmer
Skimmers
ESI
Needle
ESI
Needle
LaserVision
OPO/OPA
1. Create an anaerobic
environment
Tunable
IR
2mM [EMIM][I]
2. Use ion source to reveal activated
-1
in H2O/MeCN precursor 600-4500 cm
Heated
Capillary
MCP
Detector
Det
0
500
1000
1500
2000
2500
Photon Energy (cm-1)
3000
3500