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1
La-Mediated Bond Activation, Coupling, and Cyclization of 1,3-butadiene Probed by
Mass-Analyzed Threshold IonizationSpectroscopy
Department of Chemistry
University of Kentucky
Dilrukshi Hewage, Ruchira Silva and Dong-Sheng Yang
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
3
M
C
C
H
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.
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
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Spectroscopy ChamberReaction
Chamber
ND:YAG(355 nm)
ND:YAG (532 nm)
Dye laserFrequency Doubling
Electronics
Diffusion Pump
Turbo Pump
Experimental Setup
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Extraction Cans
TOF Tube
MCP Detector
Reaction Chamber
Metal Rod
Nozzle
Laser(532 nm)Carrier Gas &Hydrocarbon
Spectroscopy Chamber
8
Extraction Cans
TOF Tube
MCP Detector
Source Chamber
Spectroscopy Chamber
UV
ML+
ML
320 V/cm
9
Extraction Cans
TOF Tube
MCP Detector
Source Chamber
UV
MATI ions Promt ionsPromt ions MATI ionsT=0 TOF
spectrum
Spectroscopy Chamber
Theoretical Calculations
DFT-B3LYP for geometry optimization and frequency calculation
La ([Xe] 6s25d1) : SDD (Stuttgart/Dresden relativistic effective core potential)
C and H : 6-311+G(d,p)
Spectral simulation
Franck-Condon factors and Boltzmann distribution
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12
La+1,3-butadiene
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TOF-MS of La+1,3-butadiene @ 225nm
Time / us
Rel
ativ
e in
ten
sity
La
LaO
LaC
2L
aC2H
2
LaC
4H4L
aC4H
2
LaC
4H6
LaC
6H8
LaC
6H6
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TOF-MS of La+1,3-butadiene @ 225nmL
aC2H
2
LaC
4H4
LaC
4H6
LaC
6H8
LaC
6H6
Liu, Y.; Kumari, S.; Roudjane, M.; Li, S.; Yang, D.-S. Journal of Chemical Physics 2012, 136, 134310
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36000 37000 38000 39000 40000 41000
PIE Spectra
Wavenumber / cm-1
LaC6H6 LaC4H6
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LaC4H6
Rel. Energy 0 3625
A B
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39000 39200 39400 39600 39800 40000 40200 40400
Experimental MATI Spectrum & Simulation
Wavenumber / cm-1
1A' ← 2A' , 40178
1A ← 2A , 41730
39404
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39000 39500 40000 40500
Wavenumber / cm-1
1A' ← 2A' @ 200K
400370320
285470
24(a)
(b)
(c)
(a)
(c)
(b)
Experiment
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Geometry of the Complex Geometry parameter
Neutral Ion
La-C1 2.51 2.44
La-C2 2.67 2.62
C1-C2 1.45 1.45
C2-C3 1.39 1.39
< C1LaC4 75 0 76 0
< LaC1H1 130 0 128 0
< LaC1C2H1 1190 1210
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Bonding of the Complex
C1
C2
C4
C3
C1
C2
C4
C3
C1-C2 = C3-C4 > C2-C3
M-C1 < M-C2
C1-C2 C2-C3 La-C1 La-C2
1.45 1.39 2.51 2.67
Diamond, G. M.; Green, M. L. H.; Walker, N. M.; Howard, J. A. K.; Mason, S. A. J. Chem. Soc. Dalton Trans. 1992, 2641
C1-C2 = C3-C4 < C2-C3
M-C1 > M-C2
C1C2
C3C4
σ2 , π metallacyclopentene π2 model
Bond lengths are in Å
1.34
1.46
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TOF of La+1,3-butadiene @ 225nmL
aC2H
2
LaC
4H4
LaC
4H6
LaC
6H8
LaC
6H6
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36600 36800 37000 37200 37400 37600 37800 38000
MATI Spectrum of LaC6H6
Wavenumber / cm-1
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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
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SummaryL
aC2H
2
LaC
4H4
LaC
4H6
LaC
6H8
LaC
6H6
Structures and electronic states of the products
Experimental ionization energies and vibrational frequencies
33
Thank you