C‐H Bond Activation of Aromatic Systems

Josh Wilson

Dr. Eric PattersonDr. Eric Patterson

Bond Dissociation Enthalpy TableBond Dissociation Enthalpy Table

B d B d Di i ti E th l (k l/ l)Bond Bond Dissociation Enthalpy (kcal/mol)

H‐H 104

CH3‐H 104

CH3‐Br 70

CH3CH2‐H 98

CH3‐CH2‐Br 68CH3 CH2 Br 68

(CH3)2CH‐H 95

(CH3)2Ch‐Br 68

(CH3)3C‐H 91

(CH3)3C‐Br 65

Ph‐H (aromatic) 113

XPi Donating (Strong Activators)‐OH, ‐OCH3, ‐NH2, ‐NHCOCH32 3

Sigma Donors (Activating)‐CH3, ‐Ar

Halogens (Weakly Deactivating)‐Br, ‐Cl, ‐F

Pi Withdrawing (Strong Deactivators)‐COOH, ‐COCH3, ‐COOCH3, ‐NO2

Others‐CF3, ‐CN, No Sub

Pi Donating MechanismPi Donating Mechanism

Sigma Donating Mechanism ( )(para)

Sigma Donating Mechanism( )(meta)

Pi Withdrawing MechanismPi Withdrawing Mechanism

Studied ReactionStudied Reaction

Level of TheoryLevel of Theory

• Density Functional TheoryDensity Functional Theory• M06‐2X

• Basis Set• Basis Set• 6‐31+G(d,p) on all atoms but Pd• SDD on PdSDD on Pd

• Solvation• SMD• SMD

S b tit t H tt Si S b tit t H tt SiSubstituent Hammett Sigma Constant (para)

Substituent Hammett SigmaConstant (para)

Pi Donating Groups Pi Withdrawing Groups

‐NH2 ‐0.66 ‐COOH 0.45

‐OH ‐0.37 ‐COOCH3 0.45

‐OCH3 ‐0.27 ‐COCH3 0.50

‐NHCOCH3 ‐0.15 ‐NO2 0.78

Sigma Donating Groups Other

‐CH ‐0 17 ‐CF 0 54CH3 0.17 CF3 0.54

‐Ar ‐0.01 ‐CN 0.66

Halogens ‐No Sub 0.00

‐Br 0.23

‐Cl 0.23

‐F 0.06

Enthalpy in Aqueous Environment

NH2 88

89

90

OH

OCH3

CH3

A

None

5 439 85 121

86

87

l) Ar

F

ClBr

y = ‐5.439x + 85.121R² = 0.9258

84

85

Enthalpy

 (kcal/mol

COOCH3COOH

COCH3

CN

81

82

83

NO2

79

80

81

‐0.8 ‐0.6 ‐0.4 ‐0.2 0 0.2 0.4 0.6 0.8 1

Sigma

Free Energy in Aqueous Environment

88

89

NH2

OHCH3

None85

86

87

OCH3Ar

F

ClBr

y = ‐5.3606x + 84.209R² = 0.9144

83

84

85

Energy (k

cal/mol)

COOCH3COOH

COCH3

CN

Cl

81

82Free E

NO279

80

78‐0.8 ‐0.6 ‐0.4 ‐0.2 0 0.2 0.4 0.6 0.8 1

Sigma

Possible Mechanism #1Possible Mechanism #1

Possible Mechanism #2Possible Mechanism #2

Enthalpy

y = ‐2.2038x + 13.687R² = 0.9165

16

18

12

14

l)

8

10

Enthalpy

 (kcal/mol

4

6

0

2

‐0.8 ‐0.6 ‐0.4 ‐0.2 0 0.2 0.4 0.6 0.8 1

Sigma

Free Energy

6

7

y = ‐2.2141x + 4.4667R² = 0.8665

ol)

3

4

ree En

ergy (k

cal/mo

2

Fr

0

1

‐0.8 ‐0.6 ‐0.4 ‐0.2 0 0.2 0.4 0.6 0.8 1

Sigma

Enthalpy Comparisons

y = ‐5.2298x + 85.062R² = 0.9121

80

90

100

60

70

80

l)

40

50

60

Enthalpy

 (kcal/mol

Benzene System

Pd System

y = ‐2.2038x + 13.687R² 0 9165

20

30

R² = 0.9165

0

10

‐0.8 ‐0.6 ‐0.4 ‐0.2 0 0.2 0.4 0.6 0.8 1

Sigma

Free Energy Comparisons

y = ‐4.972x + 84.201R² = 0.8804

80

90

100

60

70

80

ol)

40

50

60

ree En

ergy (k

cal/mo

Benzene System

Pd System

20

30

Fr

y = ‐2.2141x + 4.4667R² = 0.866

0

10

‐0.8 ‐0.6 ‐0.4 ‐0.2 0 0.2 0.4 0.6 0.8 1

Sigma

Where do we go from here?Where do we go from here?

• Transition State of ReactionTransition State of Reaction• Fine tune bipy‐Pd ligand

i i h h li d• Experiment with other ligand systems• Develop working catalyst for C‐H bond activation

AcknowledgementAcknowledgement

• Dr Eric PattersonDr. Eric Patterson• Dr. Colleen Munro‐Leighton

S• NSF