4.2 C–N Bond Formation
101
4-14
0.0
(kcal/mol)
4-16
8.4
4-17ts
28.7
4-18
-10.3
4-19ts
-2.7
G(B3-LYP-D3, 1,2-dichloroethane)
notrogen extrusion
migratory insertion
4-20
-53.7
4-21
-50.0
4-22ts
-33.4
C-H bond cleavage
4-14
-64.0
4-23
4-14
4-15
2-PhPy
N
Ms
N 2
4-15
4-16
4-17ts
4-18
4-19ts
4-20
2-PhPy
4-21
4-22ts
2-PhPy
N
H
N Ms
4-23
Ms =
S
O
O
CH 3
N Rh
N Rh
2-PhPy
N Rh
N
Ms
N 2
N Rh
N
Ms
N Rh N
Ms
N 2
N Ms
N
Rh
N Ms
N
Rh
N Ms
2-PhPy
N
Rh N
N H
Ms
Fig. 4.5 Free energy profiles for Rh(III)-catalyzed intermolecular C–H bond activation and
amination of arenes with azides. The values are the relative energies given in kcal/mol calculated at the B3-LYP-D3/6-31G(d)/SRSC-ECP//B3-LYP/6-31G(d)/SRSC-ECP level of theory in
1,2-dichloroethane
of nitrene precursors to construct C(aryl)-N(amido) bonds. In this chemistry, dioxazolones are more convenient to prepare, store, and use compared to the corresponding
azides, which can release gaseous carbon dioxide to formally form an acylnitrene.
Moreover, this new strategy was found to be highly efficient over a broad range of
substrates with high functional group tolerance releasing carbon dioxide as a single
byproduct (Scheme 4.6).
DFT calculations were taken to compare the reactivity of azide and dioxazolone
in nitrenation step. As shown in Fig. 4.7, a five-membered rhodacycle 4-24 can
be formed through pyridyl-directed C–H bond activation, which is set to relative
zero. Dioxazolone can be activated by the coordination onto Rh in complex 4-26,
which leads to decomposition with the release of gaseous carbon dioxide. In Rhassisted dioxazolone decomposition transition state 4-27ts, the breaking N–O and O–
C bonds are 2.49 and 1.63 angstrom, respectively, which reveal a concerted process.
The calculated energy barrier for this step is only 15.1 kcal/mol. As a contrast, the
1.0 mol % [Cp*RhCl 2 ] 2
4.0 mol % AgNTf 2
+
N
O
N
O
O
R
1,2-DCE, 40 ºC, 12h
N
NH
R
O
72 - 98 % yield
Scheme 4.6 Rh(III)-catalyzed C–H bond activation and amidation reaction of 2-phenylpyridine
with 1,4,2-dioxazol-5-ones
101
4-14
0.0
(kcal/mol)
4-16
8.4
4-17ts
28.7
4-18
-10.3
4-19ts
-2.7
G(B3-LYP-D3, 1,2-dichloroethane)
notrogen extrusion
migratory insertion
4-20
-53.7
4-21
-50.0
4-22ts
-33.4
C-H bond cleavage
4-14
-64.0
4-23
4-14
4-15
2-PhPy
N
Ms
N 2
4-15
4-16
4-17ts
4-18
4-19ts
4-20
2-PhPy
4-21
4-22ts
2-PhPy
N
H
N Ms
4-23
Ms =
S
O
O
CH 3
N Rh
N Rh
2-PhPy
N Rh
N
Ms
N 2
N Rh
N
Ms
N Rh N
Ms
N 2
N Ms
N
Rh
N Ms
N
Rh
N Ms
2-PhPy
N
Rh N
N H
Ms
Fig. 4.5 Free energy profiles for Rh(III)-catalyzed intermolecular C–H bond activation and
amination of arenes with azides. The values are the relative energies given in kcal/mol calculated at the B3-LYP-D3/6-31G(d)/SRSC-ECP//B3-LYP/6-31G(d)/SRSC-ECP level of theory in
1,2-dichloroethane
of nitrene precursors to construct C(aryl)-N(amido) bonds. In this chemistry, dioxazolones are more convenient to prepare, store, and use compared to the corresponding
azides, which can release gaseous carbon dioxide to formally form an acylnitrene.
Moreover, this new strategy was found to be highly efficient over a broad range of
substrates with high functional group tolerance releasing carbon dioxide as a single
byproduct (Scheme 4.6).
DFT calculations were taken to compare the reactivity of azide and dioxazolone
in nitrenation step. As shown in Fig. 4.7, a five-membered rhodacycle 4-24 can
be formed through pyridyl-directed C–H bond activation, which is set to relative
zero. Dioxazolone can be activated by the coordination onto Rh in complex 4-26,
which leads to decomposition with the release of gaseous carbon dioxide. In Rhassisted dioxazolone decomposition transition state 4-27ts, the breaking N–O and O–
C bonds are 2.49 and 1.63 angstrom, respectively, which reveal a concerted process.
The calculated energy barrier for this step is only 15.1 kcal/mol. As a contrast, the
1.0 mol % [Cp*RhCl 2 ] 2
4.0 mol % AgNTf 2
+
N
O
N
O
O
R
1,2-DCE, 40 ºC, 12h
N
NH
R
O
72 - 98 % yield
Scheme 4.6 Rh(III)-catalyzed C–H bond activation and amidation reaction of 2-phenylpyridine
with 1,4,2-dioxazol-5-ones