Chemistry Reference
In-Depth Information
NO
2
O
O
O
O
O
O
S
S
S
N
N
N
PhI
PhI
PhI
184
185
183
TsN=IPh
NsN=IPh
Figure 4.12.
Commonly used nitrene precursors.
R'
Necessary for sufficient reactivity
N
H
Ph
I
NR'
PhI(O
2
CR)
2
M
EWG
R'NH
2
N
Modulates selectivity
M
H
M
N
EWG = electron-withdrawing group
PhI
R'
Figure 4.13.
Metal nitrene properties and reactions.
4.3.2. Catalysts for Metal Nitrenoid C - H Insertion
4.3.2.1. Ru(II) and Mn(III) Porphyrin Complexes
Intermolecular C - H amination
with metal porphyrins as catalysts was fi rst reported with Mn-porphyrin complexes
[251,252] . C -H amination via the intermediate metal nitrenoid species often competes
with aziridination, but upon using electron-defi cient ruthenium [243,244,247,253,257,258] ,
manganese [78,243,249,250,253,259,260], and rhodium [71,77,248,261,262] porphyrin
complexes, exclusive C-H amination has been observed [251].
Metal porphyrin - catalyzed C -H amination has been attempted with benzylic, allylic,
and hydrocarbon systems with arylimidoiodinanes as nitrene sources [249,251]. Recently,
a wider array of Mn(III) and Ru(II) porphyrins have been successfully employed in such
reactions with high conversions and yields [78,243,253]. Che and coworkers reported that
the porphyrin complex
188
(Fig. 4.14) is a very active catalyst for intermolecular C- H
amination of hydrocarbons using PhI=NTs as a stoichiometric reagent [253]. Turnover
numbers up to 2600 were reported for amination of indane. Many other activated systems
were reported to undergo effective amination without using large excess of substrate.
Furthermore, it was demonstrated that a mixture of PhI(OAc)
2
and the desired sulfon-
amide can be used as the nitrene source rather than preformed ArSO
2
N = IPh [253] .
Chiral Mn(III) and Ru(II) porphyrin complexes
186
and
187
have been reported as effec-
tive catalysts for enantioselective intermolecular amidation of benzylic methylene posi-
tions of ethylsubstituted aromatics in 45-58% ee in up to 85% yield [78].
4.3.2.2. Ru(II) and Mn(III) Salen Complexes
During efforts to improve the catalytic
activity of Mn-salen catalysts for catalytic aziridination of cyclohexene, Katsuki and
