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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

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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

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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

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Extraction Cans

TOF Tube

MCP Detector

Source Chamber

Spectroscopy Chamber

UV

ML+

ML

320 V/cm

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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

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Thank you