Anions 2007Azolide Ion Chemistry

Park City, UTJuly, 2007

Takatoshi Ichino, Shuji Kato, Stephanie VillanoJohn Stanton and Veronica M. Bierbaum

Carl LinebergerJILA and Department of Chemistry

University of Colorado

Happy 59th, Ken!!&

Thanks for everything, Jack!

Outline and Rationale• Theory ⇐⇒ experiment, synthesis,• Selected ion flow tube (SIFT) and flowing afterglow

– Gas phase synthesis of nitrogen-rich ions– Characterization of stability and structure

• Reaction chemistry: acidity, collisional dissociation, structure

• Anion photoelectron spectroscopy– Electron binding energies, ground state surface properties– Low-lying excited states, structure, bond strengths– Simulations of spectra using calculated structures– Most B3LYP/6-311++G(d,p)– Most useful with small geometry changes– Can be problematic with moderate ones: CH2

-, SF6-, . . .

– Useful with very large changes: isomers, conformers, clusters– Vibronic coupling raises complex issues (ignored here today)

Azolides and related anions

-

Pyrazole (vibronic coupling)N-methyl pyrazole (deprotonation site ID)N-methyl imidazole (selective reactions)Vinyl diazomethyl anion (conformational selectivity)1H -1,2,3 triazole (everything happens)

C5-nH5-nNn-

Azolides formed by OH- deprotonation of azoles at known T

Negative Ion Photoelectron Spectrometer

B

E x BMass Filter

I(KE)e-

He

m wave

Roots Pump

uv laser351 nm

Reagents

LN2 jacket

A-R-

hν + A- → A + e- (KE)

10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

0m/z

N

m/z 66

0

400

800

1200

1600

10 20 30 40 50 60 70 80 90 1000m/z

-

NN

m/z 67

Generation of M-1 Anions Via OH- Deprotonation

Note m/e = 40 second product

Other reactions appear to haveonly one ionic product.10 20 30 40 50 60 70 80 90 100

0

1000

2000

3000

4000

0m/z

NN

N

m/z 68

Negative Ion Photoelectron Spectroscopy

AB– + hν AB +e–

hν

EA(AB)VDE(AB–)

AB–

AB

←Electron binding energy

Intensities governed by Franck-Condon factorsInstrument resolution is 5 meV (40 cm-1 or 0.1kcal/mol)ΔS= ± 1 selection ruleUse DFT calculations and full FCF simulation to compare with exp.

O2- and O2 Electronic Potentials

R, Angstrom

Ener

gy, c

m-1

How well can one fit the observed photoelectron spectrumby optimizing O2

- properties: re, ωe, S-O, and EA?

1.0 2.0 3.0

0

20,000

40,000

O2- 2Π1//2, 3/2

O21Σ

O21Δ

O23Σ

O2- photoelectron spectrum simulation

K. Ervin, I. Anusiewicz, P. Skurski, J. Simons and WCL,J. Phys Chem. A 107, 8521 (2003)

EA=1.161 eV

Phot

oele

ctro

n C

ount

s

0

1 0 0

2 0 0 R o t a t io n a l /S p in - O r b i tC o n t o u r

EA=1.161 eV

0 . 51 . 01 .52 .02 . 53 . 00

1 0 0

2 0 0

electron binding energy, eV

3Σ 0−01Δ 0−0

1Σ 0−0

EA(O2)

Fit

Experiment

C4 C3

N2N1

C5

H H

C4 C3

N2N1

C5

H

H

C4 C3

N2N1

C5

H

H

C4 C3

N2N1

C5

H

C4 C3

N2N1

C5

H

H

+ HO + H2O

H

HH

+ H2OH

H

H+ H2O

H

+ H2O

ΔrxnHo

- 35.4 kcal mol-1

(exp -36.7 ± 0.4)

- 5.8 kcal mol-1

+ 9.9 kcal mol-1

+ 6.6 kcal mol-1

pyrazole 1-pyrazolide

3-pyrazolide

4-pyrazolide

5-pyrazolide

Pyrazole reactions with hydroxide

-5.8 kcal mol-1

All are m/e =66

-6 kcal/mol

-35 kcal/mol

Electron Binding Energy (eV)

2.02.22.42.62.83.03.2

C5C4 C3

N2N1H

H

H

H

pyrazolide anions photoelectron spectrum

5-pyrazolyl

1-pyrazolyl

Test assignments by “blocking” N1 site with CH3.

N-methyl-pyrazole reactions with OH-

C

C C

NNCH3

H

5C

4C C3

N2N1CH3

H

H

C

C C

NNCH2

H

H

C

C C

NNCH3

H

C

C C

NNCH3

H

+ HO

ΔrxnH0

+ H2O

+ H2O

+ H2O

+ H2O

H

H

H

H

H

-5.0 kcal mol-1

+1.4 kcal mol-1

+7.9 kcal mol-1

+11.3 kcal mol-1

All are m/e =71

Electron Binding Energy (eV)

1.82.02.22.42.62.83.03.23.4

C

C C

NNCH3

H H

Electron Binding Energy (eV)

electron binding energy, (eV)

1.82.02.22.42.62.83.03.23.4

2A"

2A'Ab initio simulation

N-methyl-5 -pyrazolide photoelectron spectrum

Simulation is convincing confirmation of C5 deprotonation.

Electron Binding Energy (eV)

1.82.02.22.42.62.83.03.23.4

C

C C

NNCH3

H H

Electron Binding Energy (eV)

electron binding energy, (eV)

1.82.02.22.42.62.83.03.23.4

2A"

2A'Ab initio simulation

N-methyl-5 -pyrazolide photoelectron spectrum

What will happen when more reaction channels are open?

N-methyl-imidazole reactions with OH-

C

C N

CNCH3

H

H

5C

4C N3

C2N1CH3

H

H

H

C

C N

CNCH2

H

H

H

C

C N

CNCH3

H

H

C

C N

CNCH3

HH

+ HO

ΔrxnH0

+ H2O

+ H2O

+ H2O

+ H2O

-2.5 kcal mol-1

-1.7 kcal mol-1

-0.9 kcal mol-1

+15.5 kcal mol-1

C

C N

CNCH3

H

H

C

C N

CNCH3

H

H

All are m/e =71

N-methyl imidazolide pe spectrum

Electron Binding Energy, (eV)1.21.62.02.42.83.2

Phot

oelect

ron

Coun

ts

2.02.12.2

a

b

cd

e

a

y

x

How well does the simulation reproduce the detailed structure?

N-methyl imidazolide expanded view of simulation & experiment

Electron Binding Energy, (eV)

1.952.002.052.102.152.202.25

Phot

oele

ctro

n C

ount

s

C

C N

CNCH3

H

H

C

C N

CNCH3

H

H

C

C N

CNCH3

H

H

But which anion structure(s) are present?

electron binding energy, eV

0.51.01.52.02.53.0

N-methyl imidazolide pes simulations

C

C N

CNCH2

H

H

H

C

C N

CNCH3

H

H

C

C N

CNCH3

H

H

C

C N

CNCH3

H

H

C

C N

CNCH3

H

H

data

simulation

simulation

simulation

electron binding energy, eV

0.51.01.52.02.53.0

N-methyl imidazolide pes simulations

C

C N

CNCH2

H

H

H

C

C N

CNCH3

H

H

C

C N

CNCH3

H

H

C

C N

CNCH3

H

H

C

C N

CNCH3

H

H

data

simulation

simulation

simulation

Only the C5 deprotonation product is present in significantyield, although all three isomers are energetically accessibleWhat is the “blob” at lower eBE? Same mass. Ring open?

Vinyldiazomethyl (vdm) anion chemistry

N NC

CC

H

HH

CN

H2CCN

H2CCCH

H3CCN

HCN

N2

_

collisionalactivation

path a

path b

+_

+_

+path c

_

H2CCHCNNpath d

_

+26 kcal mol-1

+31 kcal mol-1

+4.4 kcal mol-1

+40 kcal mol-1

C

C

H H

H C

NN

_H2O+

CCC

H H

H H

H

N2O+_

CC

H H

H CNN

_H2O+

Produce the ring open form in reaction of allyl anion with N2O.

Both E- and Z- conformations of vdm- may be present

Vinyldiazomethyl anion pes

Electron Binding Energy (eV)1.82.02.22.42.62.83.03.2

Phot

oele

ctro

n Co

unts

A 2A'

X 2A"CC

H H

H CNN

_

Can simulations differentiate between E- and Z- conformers?

Vinyldiazomethyl anion chemistry

Electron Binding Energy (eV)1.81.92.02.12.2

Z-vinyldiazomethyl

CC C

NN

H

H

H

_

E-vinyldiazomethyl

CC

H H

H CNN

_

Yes!

So we will use this capability to look at a complex reaction.

1H-1,2,3 triazole reaction with OH-

OH- + C2N3H3 → (m/e 68)- + H2O major product→ (m/e 40)- + neutral(s) smaller

NN

NH

H

H

Gentle CID on m/e 68 gives extensive m/e = 40 anion(s)

What are the identities, structures and energeticsof these anions?

Can we infer plausible reaction mechanisms?

1,2,3,triazolide imaging pe spectrum

electron binding energy (eV)3.403.453.503.553.603.653.70

Phot

oelect

ron

coun

tsN

NN

H H

-actuallym/e = 68

355, 335, 320 nm images

electron binding energy, eV3.33.43.53.63.73.8

phot

oelect

ron

coun

ts

NN

N

H H

-

m/e = 68

But there is photoelectron signal at lower binding energies.

electron binding energy, eV

1.82.02.22.42.62.83.03.2

Phot

oelect

ron

Coun

tsm/e = 68 photoelectron spectrum

x 10

And there is the other m/e = 40 reaction product:

Electron Binding Energy (eV)

1.41.61.82.02.22.42.62.83.03.2

Phot

oelect

ron

Coun

ts

m/e = 40 photoelectron spectrum

So how do we rationalize all these data?

Triazole N1 deprotonation by OH-

0

−62.3

−47.2

HO_

+NN

NH

H

H

C NN

NCH

H

_

H2O C CN

NN

H H

_H2O+

m/e=68

electron binding energy (eV)3.403.453.503.553.603.653.70

Phot

oelect

ron

coun

ts

1,2,3,triazolide imaging pe spectrum

NN

N

H H

-

EA = 3.447(4) eV

What are the identities, structures andformation mechanisms for the minor reaction products?

Indirect C4 deprotonation within complex

HO_

+NN

NH

H

H

C NN

NCH

H

_

H2O

C NN

NCH

H

_ H2O

C CN

NN

H H

_H2O+

−47.2

m/e=68

0

−62.3 −62.2

HO_

+NN

NH

H

H

NN

NH H

HOH

_

−4.2

−22.7

−3.2

m/e=68

NN

N

_H2O+

H H

C4 deprotonated product observed

E le c t r o n B in d in g E n e rg y (e V )

1 .82 .02 .22 .4

Phot

oelect

ron

Coun

ts

NN

N

_

H Hsimulation

m/e =68 data

0

−17.0

+0.1

−27.4

−2.5

+3.0

−14.9

−19.0

−31.7

HO_

+NN

NH

H

H

NN

NH

H

HOH

_

NN

NH

H

HOH

_NC

H

H CNN

H2O_NC

H CNN

H2O_

H

NC

H CNN

_H2O+

H

NC

H

H CNN

_H2O+

NN

NH

_H2O+

H

NC

H CNN

H2O_

H

C4 attack by OH-leads to ring opening

70 %

30 %

−3.2

m/e=68

Electron Binding Energy (eV)

2.42.52.62.72.8

Both conformers are present

NC

H

H CNN

_

NC

H CNN

_

H

m/e = 68 data

Simulation

Simulation

0.7 A + 0.3 B

0

−33.4

−17.2 −15.5

−32.4

−60.4

HO_

+NN

NH

H

H

NN

N

H

H

HOH _

NN

N

H

H_HOH

NN

N

H

H

_H2O+

N C CH

H

H2ON2

_

++

C C NH

H

H2O

_

++

N2

m/e=68

m/e=40

m/e= 40?

ketenimine

C5 attack also leads to ring opening

electron binding energy, eV1.41.61.82.02.22.4

Phot

oelect

ron

Coun

ts

Improved m/e = 40 data

Very likely two species in spectrum. Try to model them.

Phot

oelect

ron

Coun

ts

E lectron Binding Energy (eV)

1.41.61.82.02.22.4

C C NH

H

_

data

authentic

subtractedN C C

H

H _

Both m/e = 40 products are present

X 2A”

In Conclusion . . .The combination of flowing afterglow ion chemistry

and anion photoelectron spectroscopy can provide unique data on the structure, energetics and reactions of highly unstable species.

HAPPY BIRTHDAY, KEN!!!!