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?