Towards Isolation of Organometallic Iridium Catalytic Intermediates Arron Wolk Johnson Laboratory...
-
Upload
nickolas-montgomery -
Category
Documents
-
view
221 -
download
0
Transcript of Towards Isolation of Organometallic Iridium Catalytic Intermediates Arron Wolk Johnson Laboratory...
Towards Isolation of Organometallic Iridium Catalytic Intermediates
Arron WolkJohnson Laboratory
Thursday, June 20th, 2013
Characterizing the Potential Landscape
Electrospray Ionization
Reaction Mixture Reaction Coordinate
CatalystReactants
Activated Catalyst
Catalyst/SubstrateComplexes
Cryogenic Cooling
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 ))(())((
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
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
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
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
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
+ +
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
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
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
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.)
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
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+
+
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
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
First Steps in Activation of Catalyst
NO
Ir3+
+
+O + +
Catalytic Reaction Mixture
First Oxidation Second Oxidation
On to thedimer
Thanks
• Mark Johnson• Christopher Johnson• Joseph Fournier• Johnson Laboratory
• Ulirich Hintermair, Crabtree Group• Andrew Ingram, Zare Group• Ohio Molecular Spectroscopy Organizers
Extra Slides
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
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?
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
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?