1. La-Mediated Bond Activation, Coupling, and Cyclization of 1,3-butadiene Probed by Mass-Analyzed Threshold Ionization Spectroscopy Department of Chemistry University of Kentucky Dilrukshi Hewage, Ruchira Silva and Dong-Sheng Yang 1

2. Motivation  Significant role in organic synthesis and catalysis  Many kinetic studies in the gas phase, but very few spectroscopic measurements  Identify structures and investigate reaction pathways  Benchmark to test theoretical models and to design tailored catalyst 2

3. Background C-C bond strength ≈ 348 kJmol -1 C-H bond strength ≈ 418 kJmol -1 C-C bond activation  Less common than C-H activation. Why?  C-C bonds are less abundant than C-H bonds  C-C bonds are highly directional. 3 Hinrichs, R. Z.; Schroden, J. J.; Davis, H. F. J. Phys. Chem. A 2008, 112, 3010 Siegbahn, P.E.M.; Blomberg, M.R.A. J. Am. Chem. Soc. 1992, 114, 10548

4. Previous Studies  Cross molecular beam studies on M + C n H n have revealed the product distribution and their energy distribution Ex: Y + C 2 H 2 → YC 2 + Y-C 2 H  Fast flow reactor methods have revealed the kinetics  Theoretical studies on reaction pathways Glendening, E. D. Journal of Physical Chemistry A 2004, 108, 10165 Porembski, M.; Weisshaar, J. C. Journal of Physical Chemistry A 2001, 105, 6655 4

5. Spectroscopy Chamber Reaction Chamber ND:YAG(355 nm) ND:YAG (532 nm) Dye laser Frequency Doubling Electronics Diffusion Pump Turbo Pump Experimental Setup 5

6. 6 Reaction chamber Spectroscopy chamber Piezo valve & Face plate Skimmer Diffusion pump Extraction Cans TOF MCP Turbo pump Micro motor Deflection plates

7. 7 Extraction Cans TOF Tube MCP Detector Reaction Chamber Metal Rod Nozzle Laser(532 nm) Carrier Gas & Hydrocarbon Spectroscopy Chamber

8. 8 Extraction Cans TOF Tube MCP Detector Source Chamber Spectroscopy Chamber UV ML + ML 320 V/cm

9. 9 Extraction Cans TOF Tube MCP Detector Source Chamber UV MATI ions Promt ions MATI ions T=0 TOF spectrum Spectroscopy Chamber

10. Ion Neutral + UV laser 320 V/cm Rydberg states Extraction Can 1 ~ 5-20VDC 10

11. Theoretical Calculations  DFT-B3LYP for geometry optimization and frequency calculation La ([Xe] 6s 2 5d 1 ) : SDD (Stuttgart/Dresden relativistic effective core potential) C and H : 6-311+G(d,p)  Spectral simulation Franck-Condon factors and Boltzmann distribution 11

12. La+1,3-butadiene 12

13. TOF-MS of La+1,3-butadiene @ 225nm Time / us Relative intensity La LaO LaC 2 LaC 2 H 2 LaC 4 H 4 LaC 4 H 2 LaC 4 H 6 LaC 6 H 8 LaC 6 H 6 13

14. TOF-MS of La+1,3-butadiene @ 225nm LaC 2 H 2 LaC 4 H 4 LaC 4 H 6 LaC 6 H 8 LaC 6 H 6 14 Liu, Y.; Kumari, S.; Roudjane, M.; Li, S.; Yang, D.-S. Journal of Chemical Physics 2012, 136, 134310

15. PIE Spectra Wavenumber / cm -1 LaC 6 H 6 LaC 4 H 6 15

16. MATI of LaC 2 H 2 520 800 490 41163 16

17. Experimental & Simulated Spectra 520 / 528 800 / 832 490 / 471 800 / 814 IP= 41163 / 41908 1 A 1 ← 2 A 1, 200 K 17

18. LaC 4 H 6 Rel. Energy 0 3625 A B 18

19. Experimental MATI Spectrum & Simulation Wavenumber / cm -1 1 A' ← 2 A', 40178 1 A ← 2 A, 41730 39404 19

20. Wavenumber / cm -1 1 A' ← 2 A' @ 200K 400 370 320 285 470 24 (a) (b) (c) (a) (c) (b) 20 Experiment

21. Simulation 25 1 0 24 1 0 270/280 264/360 25 0 1 24 0 1 22 0 1 411/393 320/309500 24 0 1 25 0 1 24 0 2 22 0 1 24 0 1 IP / cm -1 39414 40036 1 A’ ← 2 A’ 21

22. Geometry NeutralIon LaC 1 2.512.44 LaC 2 2.672.62 C1C2C1C2 1.45 C2C3C2C3 1.39 < C 1 LaC 4 75 0 76 0 < LaC 1 H 1 130 0 128 0 < LaC 1 C 2 H 1 119 0 121 0 C3C3 C2C2 C1C1 C4C4 H1H1 H2H2 22

23. Geometry of the Complex Geometry parameter NeutralIon La-C 1 2.512.44 La-C 2 2.672.62 C1-C2C1-C2 1.45 C2-C3C2-C3 1.39 < C 1 LaC 4 75 0 76 0 < LaC 1 H 1 130 0 128 0 < LaC 1 C 2 H 1 119 0 121 0 23

24. Bonding of the Complex 24 C1C1 C2C2 C4C4 C3C3 C1C1 C2C2 C4C4 C3C3 C 1 -C 2 = C 3 -C 4 > C 2 -C 3 M-C 1 < M-C 2 C 1 -C 2 C 2 -C 3 La-C 1 La-C 2 1.451.392.512.67 Diamond, G. M.; Green, M. L. H.; Walker, N. M.; Howard, J. A. K.; Mason, S. A. J. Chem. Soc. Dalton Trans. 1992, 2641 C 1 -C 2 = C 3 -C 4 < C 2 -C 3 M-C 1 > M-C 2 C1C1 C2C2 C3C3 C4C4 σ 2, π metallacyclopentene π 2 model Bond lengths are in Å 1.34 1.46

25. 25 A B ethylene C 2 H 4 + La(C 2 H 2 ) - H 2 → B propene C 3 H 6 + LaCH 2 - H 2 → A + B 1-butene La+C 4 H 8 - H 2 → A + B 1,3-butadiene La+C 4 H 6 → B

26. TOF of La+1,3-butadiene @ 225nm LaC 2 H 2 LaC 4 H 4 LaC 4 H 6 LaC 6 H 8 LaC 6 H 6 26

27. MATI Spectrum of LaC 6 H 6 Wavenumber / cm -1 27

28. MATI & ZEKE Spectra of La-Benzene Liu, Y.; Kumari, S.; Roudjane, M.; Li, S.; Yang, D.-S. Journal of Chemical Physics 2012, 136, 134310 ZEKE MATI 28

29. ZEKE and Simulation of LaC 6 H 6 Liu, Y.; Kumari, S.; Roudjane, M.; Li, S.; Yang, D.-S. Journal of Chemical Physics 2012, 136, 134310 29

30. La-Benzene E / cm -1 AIE41401 C-H wagging and in plane ring deformation of cation527 La + - benzene stretching295 Ring rocking39 30

31. ~225 ~340 31

32. Summary LaC 2 H 2 LaC 4 H 4 LaC 4 H 6 LaC 6 H 8 LaC 6 H 6 32  Structures and electronic states of the products  Experimental ionization energies and vibrational frequencies

33. Thank you 33

34. HOMO LaC 2 H 2 LaC 4 H 6 LaC 6 H 6 34