1. Towards Isolation of Organometallic Iridium Catalytic Intermediates Arron Wolk Johnson Laboratory Thursday, June 20 th, 2013

2. Characterizing the Potential Landscape Electrospray Ionization Reaction Mixture Reaction Coordinate Catalyst Reactants Activated Catalyst Catalyst/Substrate Complexes Cryogenic Cooling

3. Cryogenic Ion Processing Lowers vibrational energy to near zero point Enables Infrared Predissociation Spectroscopy He/H 2 buffer gas RF Pulsed valve Electrosprayed Ions Ions out Paul Trap at 10-100K 72747678 Time of Flight (  s) 30 ms 50 ms 40 ms 20 ms 10 ms doubly-charged parent a) b) c) d) e) trap residence time: Signal Intensity (arbitrary units) hydrogen adduct formation 5 10 15 *

4. Iridium Catalyzed Water Oxidation Highly active iridium based organometallic catalyst developed by Bob Crabtree and Gary Brudvig at Yale Utilize cryogenic ion vibrational predissociation to isolate and identify the active complex “Blue solution” Ulrich Hintermair, Yale & Andrew Ingram, Stanford

5. Follow the Proposed Catalytic Cycle UV-VIS, NMR, Resonance Raman (not seen in mass spec) Iridium Dimer Proposed Active Species Oxidation/Activation ( 20 equiv. IO 4 /IO 3 ) Loss of Cp* Ligand Cp* Ligand Focus on this step

6. 464 m/z +O +N 2 Infrared Spectra of the N 2 (or D 2 ) adducts + NaIO 4 Isolation of Oxidized Intermediates Oxidized Cp* ligands have increasingly weaker binding. Use characteristic IR signatures of oxidation to confirm breakdown of precatalyst. 460480500520540 m/z

7. Singly Oxidized Complex +O Two Possible Ionic Structures Oxidized Cp*, relevant to breakdown Fulvene complex, mass spec artifact + + + OH ligand can be lost in solution

8. Spectral Signatures to Look For Oxidized Cp*, relevant to breakdownFulvene complex, mass spec artifact Alcohol OH Stretch Characteristic Cp* stretches Hydroxide OH Stretch Characteristic fulvene stretches + +

9. 800100012001400160028003000320034003600 Photon Energy, cm -1 +O + N2N2 Two OH Stretches CH Stretches Indicates likely presence of two isomers Fingerprint region can decipher Cp* from fulvene Unoxidized Complex No significant structural change

10. h probe Reflectron Signal Time of Flight, ms probe fragment pump fragment Detector h pump (scanned) Coaxial TOF ±1.5 keV (fixed) Throw Another Laser at the Problem IR 2 MS 3 Double Resonance Spectroscopy

11. 280030003200340036003800 Photon Energy, cm -1 Looking at First Oxidation Product H-Bonded OH Probe 3505 Singly oxidized species gives two isomers Free OH Probe 3664 +O + N2N2

12. 800100012001400160028003000320034003600 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 (N 2 Prediss.)

13. pyridine modes 800100012001400160028003000320034003600 Photon Energy, cm -1 Singly Oxidized Species H-Bonded OH Free OH SDD/cam-B3LYP/6-311+G(d,p) Empirically scaled to free OH and 1610 band Cp* modes alkoxy modes +O + N2N2

14. 28003000320034003600 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 +2ON 2 Doubly Oxidized Species Pair of Isomers? Looks like the singly oxidized species +

15. 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 8001000120014001600280030003200340036003800 meta-OH One free and one bound OH ortho-OH a + 800 cm -1 ortho-OH b +1100 cm -1

16. 280030003200340036003800 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 + +2ON 2

17. First Steps in Activation of Catalyst + +O + + Catalytic Reaction Mixture First OxidationSecond Oxidation On to the dimer

18. Thanks Mark Johnson Christopher Johnson Joseph Fournier Johnson Laboratory Ulirich Hintermair, Crabtree Group Andrew Ingram, Zare Group Ohio Molecular Spectroscopy Organizers

19. Extra Slides

20. Vibrational Predissociation Spectroscopy Electrosprayed Ion Lightly Bound Tags (H 2, D 2, N 2, CO 2, Ar) OPO/OPA IR Laser “Laservision” 600 – 4500 cm -1 Evaporation h

21. Cryogenic Ion Processing Allows for generation of complexes in the cryogenic ion trap Morris, et al., Acc. Chem. Res., 2009 Nickel Cyclam Which intermediate?

22. 129133 58 Ni(cyclam) 2+ 61 Ni(cyclam) 2+ BP86/6-31+G(d,p) Ni(cyclam) 2+ ·(CO 2 ) n n=1 140160180200220 m/z n=2n=3n=4 T=100 K n=0 + CO 2 React in Cryogenic Ion Trap Now on to a more exotic metal… CO 2 Adsorption

23. 28003000320034003600 Photon Energy, cm -1 Isomer I Isomer II 3505 cm -1 3436 cm -1 Two H-bonded –OH’s One free and one H-bonded -OH +2ON 2 Doubly Oxidized Species Four OH’s?