Capture and Structural Determination of Activated Intermediates in Transition Metal Catalyzed CO 2 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 Ingram, A. J. et. al. Inorg. Chem. 53 (2014)

Features of an Activated CO 2 Activating CO 2 involves adding some electron density into the π * antibonding orbital C2 O B. M. Mahan & R. J. Myers, University Chemistry (1987) Kamrath, M. Z. et. al. J. Am. Chem. Soc. 132 (2010) THIS STEP IS IMPORTANT Photon Energy (cm -1 ) ν 3 CO 2 · – 1660 cm -1 ν 3 CO cm cm -1 Predissociation Yield (a.u.) (CO 2 ) 7 –

Features of an Activated CO 2 The CO 2 molecule will exhibit a bend in order to compensate for the extra electron density added Expect this bend between neutral CO 2 (180°) and CO 2 · – (133°) C2 O B. M. Mahan & R. J. Myers, University Chemistry (1987) 133°

Finding a CO 2 Reduction Catalyst N NN N Ni 2+ HH HH Ni(cyclam) 2+ - A well-studied catalyst for CO 2 reduction that can be readily made Electrochemistry is first used to reduce the stable Ni II compound to the active Ni I catalyst Morris, A. J. et. al. Acc. Chem. Res. 42 (2009) Ni II Ni I dz2dz2 d x 2 -y 2 d yz d xz d xy dz2dz2 d x 2 -y 2 d yz d xz d xy Extra electron necessary to bind CO 2 Reduce to Ni I

ESI Needle Temperature Controlled Ion Trap Mounted to He Cryostat Ion Optics 2m Flight Tube Wiley- McLaren TOF Reflectron DC-Turning Quad MCP Detector Nd:YAG OPO/OPA Tunable IR cm -1 Differential Aperture Skimmers Heated Capillary RF-Ion Guides Experimental Setup

A (Likely Unsuccessful) Look Into Ni(cyclam) 2+ Only get Ni II species

Photon Energy (cm -1 ) neutral CO 2 asym stretch ν3ν3 ν CH ν NH 2 ν 2 + ν 3 ν 1 + ν 3 CO 2 Pred. Yield (a.u.) Calc. Intensity BP86/tzvp Ni(cyclam) 2+ does NOT activate CO 2 A (Likely Unsuccessful) Look Into Ni(cyclam) 2+ ν 1 – symmetric stretch ν 2 - bend ν 3 – asymmetric stretch

Where to Get a Stable Ni I Species? So not any old Ni catalyst will reduce CO 2 – Need to find a stable Ni I catalyst – It turns out we have one! [Ni(bipyridine-(N 2 Me) 2 )] + = Ni(L-N 4 Me 2 ) + NN N N Ni +

Ni(L-N 4 Me 2 ) + - Getting to the Active Species collisional activation 2+ BP86/tzvp [Ni(bipyridine-(N 2 Me) 2 )] 2 (diphenyldiacetylene) 2+ [Ni(bipyridine-(N 2 Me) 2 )] +

Ni(L-N 4 Me 2 ) + - Getting to the Active Species BP86/tzvp [Ni(bipyridine-(N 2 Me) 2 )] + Left with a stable Ni I species m/z [Ni I -L (N 4 Me 2 )] +

Ni(L-N 4 Me 2 ) + - Can This Ni I Compound Activate CO 2 ? m/z +CO 2 Ni I (L-N 4 Me 2 ) Ion Signal (a.u.) Only able to tag one CO 2 molecule What is this peak at 1921 cm -1 ? BP86/tzvp neutral CO 2 asym stretch ν CH ν3ν3 ν NH ν CH 2ν 2 + ν 3 ν 1 + ν Photon Energy (cm -1 ) Predissociation Yield (a.u.) Ni(cyclam) 2+ ·CO 2 Ni(L-N 4 Me 2 ) + ·CO 2

Isotopic Substitution To Verify Band Shifts Due to CO 2 Predissociation Yield (a.u.) Photon Energy (cm -1 ) ν3ν3 ν 1 + ν 3 ν CH 2ν32ν3 Ni(L-N 4 Me 2 ) + · 12 CO 2 ν 3 = ν 13 CO asym Have a shift of the peak at 1921 cm -1 – It is the asymmetric CO 2 stretch! 2ν32ν3 ν CH Ni(L-N 4 Me 2 ) + · 13 CO 2 50 cm -1

Isotopic Substitution To Verify Band Shifts Due to CO 2 Predissociation Yield (a.u.) Photon Energy (cm -1 ) ν3ν3 ν 1 + ν 3 ν CH 2ν32ν3 Ni(L-N 4 Me 2 ) + · 12 CO 2 ν 3 = ν 13 CO asym 2ν32ν3 ν CH Ni(L-N 4 Me 2 ) + · 13 CO 2 † Subtraction The difference spectrum also highlights the separation of the ν 1 + ν 3 (†) combination band from the CH stretches ν 1 should appear at 1128 cm -1, almost 200 cm -1 red of the neutral CO 2 symmetric stretch ν 1 + ν 3 50 cm -1 Expect to see the isotopically labeled combination band in oval

Is This Red Shifted CO 2 Activated? ν3ν3 ν CH Photon Energy (cm -1 ) Predissociation Yield / Calculated Intensity Ni(L-N 4 Me 2 ) + ·CO 2 Checklist: 1. Position of ν 3 2. A nonlinear CO 2

Is This Red Shifted CO 2 Activated? ν3ν3 ν CH Photon Energy (cm -1 ) ν 3 free CO 2 ν 3 CO 2 – Predissociation Yield / Calculated Intensity Ni(L-N 4 Me 2 ) + ·CO 2 (CO 2 ) 7 – Kamrath, M. Z. et. al. J. Am. Chem. Soc. 132 (2010) Activated CO 2 asymmetric transition appears between that of the neutral and radical anion CO 2 Checklist: Position of ν 3 2. A nonlinear CO 2

Is This Red Shifted CO 2 Activated? BP86/tzvp ν3ν3 ν CH Photon Energy (cm -1 ) ν 3 free CO 2 ν 3 CO 2 – Ni(L-N 4 Me 2 ) + ·CO 2 (CO 2 ) 7 – Kamrath, M. Z. et. al. J. Am. Chem. Soc. 132 (2010) Predissociation Yield / Calculated Intensity 148° Activated CO 2 asymmetric transition appears between that of the neutral and radical anion CO 2 Checklist: Position of ν 3 A nonlinear CO 2

Is This Red Shifted CO 2 Activated? BP86/tzvp ν3ν3 ν CH Photon Energy (cm -1 ) ν 3 free CO 2 ν 3 CO 2 – Ni(L-N 4 Me 2 ) + ·CO 2 (CO 2 ) 7 – Kamrath, M. Z. et. al. J. Am. Chem. Soc. 132 (2010) Predissociation Yield / Calculated Intensity 148° Activated CO 2 asymmetric transition appears between that of the neutral and radical anion CO 2 WE ACTIVATED CO 2 !

A Closer Look at the Activated CO 2 BP86/tzvp ν3ν3 ν CH Photon Energy (cm -1 ) ν 3 free CO 2 ν 3 CO 2 – Ni(L-N 4 Me 2 ) + ·CO 2 (CO 2 ) 7 – Kamrath, M. Z. et. al. J. Am. Chem. Soc. 132 (2010) Increase intensity in the methyl CH stretches from interaction with the CO 2 Predissociation Yield / Calculated Intensity 148° WE ACTIVATED CO 2 !

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 CO 2 ! What Do We Do Next? BP86/tzvp ν3ν3 ν CH Photon Energy (cm -1 ) ν 3 free CO 2 ν 3 CO 2 – Ni(L-N 4 Me 2 ) + ·CO 2 (CO 2 ) 7 – Kamrath, M. Z. et. al. J. Am. Chem. Soc. 132 (2010) Predissociation Yield / Calculated Intensity Introduce acids to get protons on the activated CO 2 148°

We Activated CO 2 ! What Do We Do Next? BP86/tzvp ν3ν3 ν CH Photon Energy (cm -1 ) Ni(L-N 4 Me 2 ) + ·CO 2 (CO 2 ) 7 – Kamrath, M. Z. et. al. J. Am. Chem. Soc. 132 (2010) Introduce acids to get protons on the activated CO 2 Predissociation Yield / Calculated Intensity ν 3 free CO 2 ν 3 CO 2 –

We Activated CO 2 ! What Do We Do Next? BP86/tzvp Introduce acids to get protons on the activated CO Photon Energy (cm -1 )

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? Ligand Isomer DFT (S-VWN5) 1 (kJ/mol) trans-I0.98 trans-II10.16 trans-III0.00 trans-IV59.23 trans-V Adam, K. R. et. al. Inorg. Chem. 36 (1997) kT = K

Ni(cyclam) 2+ - A Look at the Ligand Calculated Intensity Photon Energy (cm -1 ) trans-III trans-I ν NHα ν NHβ ν NH-degen ν NH ν CH Pred. Yield (a.u.) Only the trans-III isomer present in the gas phase! BP86/tzvp

Transitioning From CO 2 to CO 2 · – Ni(cyclam) 2+ ·CO 2 Predissociation Yield (a.u.) ν 3 CO Photon Energy (cm -1 ) ν 3 CO 2 – neutral CO 2 asym stretch 1. Kamrath, M. Z. et. al. J. Am. Chem. Soc. 132 (2010) 2. Almlöf, J. et. al. Chem. Phys. Lett. 28 (1974) Py-CO 2 – ·(CO 2 ) 3 ν 3 (cm -1 )θ OCO R CO (Å) CO °1.162 Ni(L-N 4 Me 2 ) + ·CO °1.231 Py-CO 2 – ·(CO 2 ) ° CO 2 · – ° Ni(L-N 4 Me 2 ) + ·CO 2 (CO 2 ) 7 – The activated CO 2 appears to be an intermediate step in the transition between neutral and negatively charged CO 2 ν CN

Ni(cyclam) 2+ and Formate

Ni(cyclam) 2+ with Stuff

How Important are the NH Groups? Ni(DMC) 2+ ·(CO 2 ) n Ni(cyclam) 2+ ·(CO 2 ) n N NN N Ni 2+ HH HH n Ion Signal (a.u.) m/z 012 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? 1. Froehlich, J. D. et. al. Inorg Chem. 51 (2012) Ni(DMC) 2+ is significantly harder to tag with CO 2 than Ni(cyclam) 2+ - seems as though CO 2 binds to the NH groups

How Important are the NH Groups? N NN N Ni 2+ H 3 C H CH 3 H N NN N Ni 2+ HH HH Splitting of the NH peak observed for Ni(DMC) 2+  splitting the degeneracy of the amine group Calculations confirm position of CO 2 attachment BP86/tzvp Photon Energy (cm -1 ) Predissociation Yield (a.u.) Splitting of NH 2ν 2 + ν 3 ν 1 + ν 3 ν NH Ni(cyclam) 2+ Ni(DMC) 2+

What If We Pull on the NH Groups? Photon Energy (cm -1 ) NH stretch CH stretches Increasing Deprotonation Ni(cyclam) 2+ Ni(cyclam)(PF 6 ) + Take a look at acidity of NH groups by pulling on the protons with different conjugate bases Decreasing pK b Red shift of NH transition and increased intensity in CH stretches Ni(cyclam)(formate) + Ni(cyclam)(d-formate) + Predissociation Yield / Calculated Intenisty Increase in CH stretches not intrinsic to formate – lose CH stretch when formate is duterated

m/z

Two Nickel Based Catalysts Ni(cyclam) 2+ A well-studied and highly efficient Ni II catalyst for CO 2 reduction Electrochemistry is used to first reduce the metal center to Ni I Ni(L-N 4 Me 2 ) + A novel Ni I species not yet studied as a catalyst for the reduction of CO 2 –several bipyridine catalysts do exist though NN N N Ni + N NN N Ni 2+ HH HH

Ni(L-N 4 Me 2 ) + - Can This Ni I Compound Activate CO 2 ? m/z +CO 2 Ni I (L-N 4 Me 2 ) Ion Signal (a.u.) Only able to tag one CO 2 molecule 148° Is this really an activated CO 2 ? BP86/tzvp neutral CO 2 asym stretch ν3ν3 ν CH ν3ν3 ν NH ν CH 2ν 2 + ν 3 ν 1 + ν Photon Energy (cm -1 ) ν 3 free CO 2 ν 3 CO 2 – Predissociation Yield / Calculated Intensity Ni(cyclam) 2+ ·CO 2 Ni(L-N 4 Me 2 ) + ·CO 2 (CO 2 ) cm -1 Kamrath, M. Z. et. al. J. Am. Chem. Soc. 132 (2010)

Morris, A. J. et. al. Acc. Chem. Res. 42 (2009) Nominally use electrochemistry to reduce Ni center – Ni I the active species Did We Miss Something In The Mechanism?

Future Work Now that we have an activated CO 2, what kind of chemistry can we do with it? – Build a liquid nitrogen octopole guide to cool and tag CO 2 to Ni(L-N 4 Me 2 ) + before entering the trap – Introduce small molecules (like H 2, NO, BPh 3 ) 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 CO 2 to look at the effects of charge transfer and stabilization

Morris, A. J. et. al. Acc. Chem. Res. 42 (2009) Can Isolated Ni(cyclam) 2+ Activate CO 2 ?

A + · Tag m + h → A + · Tag n + (m-n) Tag mass Generate Ions Excite With Laser h k IVR k evap a)b) c)d) mass Isolate One Mass Second Mass Spec mass photofragments Cryogenic Ion Vibrational Predissociation (CIVP) Spectroscopy Photon Energy (cm -1 ) Predissociation Yield SarGlyH + He

ESI Needle Temperature Controlled Ion Trap Mounted to He Cryostat Ion Optics 2m Flight Tube Wiley- McLaren TOF Reflectron DC-Turning Quad MCP Detector Nd:YAG OPO/OPA Tunable IR cm -1 Differential Aperture Skimmers Heated Capillary RF-Ion Guides Experimental Setup 1.Create an anaerobic environment 2.Use ion source to reveal activated precursor

Photon Energy (cm -1 )