156
9 Carbon-Carbon Cross-Coupling Reactions
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
Oxidative Addition
Pd(PMe 3 )
Pd 13
Pd 14
Pd 4
Pd
Pd 13 /G
Pd 14 /G
Pd 4 /G
Pd n
Pd n /G
Pd(PMe 3 )
Activation
Energy (eV)
Net Charge Transfer (e
-
)
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
Pd(PMe 3 )
Pd
Pd 13
Pd 14
Pd 4
Pd 14 /G
Pd 13 /G
Activation Energy (eV)
Net Charge Flow (e
-
)
Pd n
Pd n /G
Pd(PMe 3 )
Transmetallation
Pd 4 /G
0 . 5
0 . 4
0 . 3
0 . 2
0 . 1
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
Reductive Elimination
Pd 14
Pd 13
Pd
Pd 4
Pd 14 /G
Pd 4 /G
Pd/G
Pd 13 /G
Pd(PMe 3 )
Pd n
Pd n /G
Pd(PMe 3 )
Activation Energy (eV)
Net Charge Transfer (e
-
)
a
b
c
d
2
3
4
5
6
7
8
9
0.0
0.1
0.2
0.3
0.4
0.5
Binding Enhancement Energy (eV)
Distance (Ang.)
Br
P
Fig. 9.9 Charge transfer and activation energy for free and supported Pd n , and Pd(PMe 3 ) during
a trans-metalation, b oxidative addition and c reductive elimination. d Enhance Br and P binding
energy correlated to the distance from the Pd active site to the lattice of graphene
The binding energy of both the Br and P are enhanced on the defected graphene
as compared to the free clusters, confirming that the support enhances both charge
donation and acceptance and that the graphene appears to function as a solid-state
ligand.
9.5 Search for Alternate Cheaper Catalysts
To investigate the possibility of replacing Pd with a cheaper 3d transition metal, the
activation energies for the free and supported Fe 13 , Ni 13 , and Cu 13 clusters were
calculated and compared with that for the free and supported Pd 13 clusters in the full
reaction cycle of the Suzuki reaction, as shown in Fig. 9.10. As mentioned above,
the typical Suzuki reaction proceeds via three steps: oxidative addition, transmetallation, and reductive elimination. In the charge donating oxidative addition step,
the activation energies of the free first-row transition metal clusters are significantly
lower than that of the free Pd 13 cluster. The Fe 13 cluster exhibits extremely low
9 Carbon-Carbon Cross-Coupling Reactions
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
Oxidative Addition
Pd(PMe 3 )
Pd 13
Pd 14
Pd 4
Pd
Pd 13 /G
Pd 14 /G
Pd 4 /G
Pd n
Pd n /G
Pd(PMe 3 )
Activation
Energy (eV)
Net Charge Transfer (e
-
)
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
Pd(PMe 3 )
Pd
Pd 13
Pd 14
Pd 4
Pd 14 /G
Pd 13 /G
Activation Energy (eV)
Net Charge Flow (e
-
)
Pd n
Pd n /G
Pd(PMe 3 )
Transmetallation
Pd 4 /G
0 . 5
0 . 4
0 . 3
0 . 2
0 . 1
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
Reductive Elimination
Pd 14
Pd 13
Pd
Pd 4
Pd 14 /G
Pd 4 /G
Pd/G
Pd 13 /G
Pd(PMe 3 )
Pd n
Pd n /G
Pd(PMe 3 )
Activation Energy (eV)
Net Charge Transfer (e
-
)
a
b
c
d
2
3
4
5
6
7
8
9
0.0
0.1
0.2
0.3
0.4
0.5
Binding Enhancement Energy (eV)
Distance (Ang.)
Br
P
Fig. 9.9 Charge transfer and activation energy for free and supported Pd n , and Pd(PMe 3 ) during
a trans-metalation, b oxidative addition and c reductive elimination. d Enhance Br and P binding
energy correlated to the distance from the Pd active site to the lattice of graphene
The binding energy of both the Br and P are enhanced on the defected graphene
as compared to the free clusters, confirming that the support enhances both charge
donation and acceptance and that the graphene appears to function as a solid-state
ligand.
9.5 Search for Alternate Cheaper Catalysts
To investigate the possibility of replacing Pd with a cheaper 3d transition metal, the
activation energies for the free and supported Fe 13 , Ni 13 , and Cu 13 clusters were
calculated and compared with that for the free and supported Pd 13 clusters in the full
reaction cycle of the Suzuki reaction, as shown in Fig. 9.10. As mentioned above,
the typical Suzuki reaction proceeds via three steps: oxidative addition, transmetallation, and reductive elimination. In the charge donating oxidative addition step,
the activation energies of the free first-row transition metal clusters are significantly
lower than that of the free Pd 13 cluster. The Fe 13 cluster exhibits extremely low