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Towards Isolation of Organometallic Iridium Catalytic Intermediates
Arron WolkJohnson Laboratory
Thursday, June 20th, 2013
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Characterizing the Potential Landscape
Electrospray Ionization
Reaction Mixture Reaction Coordinate
CatalystReactants
Activated Catalyst
Catalyst/SubstrateComplexes
Cryogenic Cooling
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Cryogenic Ion Processing
• Lowers vibrational energy to near zero point• Enables Infrared Predissociation Spectroscopy
He/H2 buffer gas
RF
RF
Pulsedvalve
ElectrosprayedIons Ions out
Paul Trap at 10-100K
72 74 76 78Time of Flight (ms)
30 ms
50 ms
40 ms
20 ms
10 ms
doubly-chargedparent
a)
b)
c)
d)
e)
trap residence time:
Sign
al In
tens
ity (a
rbitr
ary
units
)
hydrogen adduct formation
5
10
15
*
mBBAhBA mnn ))(())((
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Iridium Catalyzed Water Oxidation• Highly active iridium based organometallic catalyst
developed by Bob Crabtree and Gary Brudvig at Yale
NO
OHIr3+
2 H2O-8 e-, -4 H+
O2precatalyst
• Utilize cryogenic ion vibrational predissociation to isolate and identify the active complex
Oxidant
Breakdown
“Blue solution”
Ulrich Hintermair, Yale & Andrew Ingram, Stanford
Active Water Oxidation Catalyst
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Follow the Proposed Catalytic Cycle
UV-VIS, NMR, Resonance Raman(not seen in mass spec)
Ir
O
IrO
O
O
Iridium Dimer
Proposed Active Species
NO
OHIr3+
precatalyst
Oxidation/Activation( 20 equiv. IO4/IO3)
Loss of Cp* Ligand
Cp* Ligand
Focus on this step
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464 m/z
+O +O
+N2
+N2
+N2
Infrared Spectra of the N2 (or D2)
adducts
+ NaIO4
Isolation of Oxidized Intermediates
Oxidized Cp* ligands have increasingly weaker binding.Use characteristic IR signatures of oxidation to confirm breakdown of precatalyst.
NO
OHIr3+
460 480 500 520 540m/z
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Singly Oxidized Complex
+O
Two Possible Ionic Structures
NO
Ir3+
OH
Oxidized Cp*, relevant to breakdown
NO
Ir3+OH
Fulvene complex, mass spec artifact
+
+
+NO
OHIr3+
OH ligand can be lostin solution
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Spectral Signatures to Look For
NO
Ir3+
OH
Oxidized Cp*, relevant to breakdown
NO
Ir3+OH
Fulvene complex, mass spec artifact
• Alcohol OH Stretch• Characteristic Cp*
stretches
• Hydroxide OH Stretch• Characteristic fulvene
stretches
+ +
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800 1000 1200 1400 1600 2800 3000 3200 3400 3600
Photon Energy, cm-1
NO
Ir3+
+O
+
•N2
Two OH Stretches
CH Stretches
Indicates likely presence of two isomers
Fingerprint region can decipherCp* from fulvene
Unoxidized ComplexNo significant structural change
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hnprobe
Reflectron
Sig
nal
Time of Flight, ms
prob
e fr
agm
ent
pum
p fr
agm
ent
Detector
hnpump
(scanned)
Coaxial TOF
±1.5 keV
(fixed)
Throw Another Laser at the ProblemIR2MS3 Double Resonance Spectroscopy
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2800 3000 3200 3400 3600 3800
Photon Energy, cm-1
Looking at First Oxidation Product
H-Bonded OH
Probe 3505
Singly oxidized speciesgives two isomers
Free OH
Probe 3664N
O
Ir3+ +O
+
•N2
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800 1000 1200 1400 1600 2800 3000 3200 3400 3600
Photon Energy, cm-1
Relative Energies(cm-1, kcal/mol)
0, 0
+1050, 3.1
+11500, 34.0
Relative Energies(cm-1, kcal/mol)
SDD/cam-B3LYP/6-311+G(d,p)Empirically scaled to free OH and 1610 band
Free OH
Bound OH
Fulvene
Experiment(N2 Prediss.)
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pyridine modes
800 1000 1200 1400 1600 2800 3000 3200 3400 3600
Photon Energy, cm-1
Singly Oxidized Species
H-BondedOH
Free OH
SDD/cam-B3LYP/6-311+G(d,p)Empirically scaled to free OH and 1610 band
Cp* modesalkoxy modes
NO
Ir3+ +O
+
•N2
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2800 3000 3200 3400 3600
Photon Energy, cm-1
Isomer I
Probe 3436 cm-1
Two H-bonded –OH’s
Isomer II
Probe 3505 cm-1
One free and one H-bonded -OH
+2O•N2
Doubly Oxidized Species
Pair of Isomers?
Looks like the singly oxidized species
NO
Ir3+
+
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Fulvene band not evident
Doubly Oxidized Species, First Isomer
SDD/cam-B3LYP/6-311+G(d,p)Same scaling factors used above
Photon Energy, cm-1
800 1000 1200 1400 1600 2800 3000 3200 3400 3600 3800
meta-OH
One free and one bound OH
ortho-OHa
+ 800 cm-1
ortho-OHb
+1100 cm-1
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2800 3000 3200 3400 3600 3800
Photon Energy, cm-1
SDD/cam-B3LYP/6-311+G(d,p), same scaling factors used above
or
0 cm-1 +700 cm-1
+100 cm-1
Second isomer must have two hydrogen bonded OH functionalities
NO
Ir3+
+
+2O•N2
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First Steps in Activation of Catalyst
NO
Ir3+
+
+O + +
Catalytic Reaction Mixture
First Oxidation Second Oxidation
On to thedimer
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Thanks
• Mark Johnson• Christopher Johnson• Joseph Fournier• Johnson Laboratory
• Ulirich Hintermair, Crabtree Group• Andrew Ingram, Zare Group• Ohio Molecular Spectroscopy Organizers
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Extra Slides
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Vibrational Predissociation Spectroscopy
ElectrosprayedIon Lightly Bound Tags
(H2, D2, N2, CO2, Ar)
OPO/OPA IR Laser“Laservision”
600 – 4500 cm-1
Evaporation
mBBAhBA mnn ))(())((
h
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Cryogenic Ion Processing• Allows for generation of complexes in the
cryogenic ion trap
Morris, et al., Acc. Chem. Res., 2009
NH
NH HN
HN
Ni(II)
Nickel Cyclam
Which intermediate?
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129 133
58Ni(cyclam)2+
61Ni(cyclam)2+
BP86/6-31+G(d,p)
Ni(cyclam)2+·(CO2)n
n=1
140 160 180 200 220
m/z
n=2 n=3 n=4
T=100 K
n=0
+ CO2
React in CryogenicIon Trap
Now on to a more exotic metal…
CO2 Adsorption
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2800 3000 3200 3400 3600
Photon Energy, cm-1
Isomer I Isomer II
3505 cm-13436 cm-1
Two H-bonded –OH’s
One free and one H-bonded -OH
N
O
Ir
+2O•N2
Doubly Oxidized SpeciesFour OH’s?