2.3 Arylation of C(sp
2
)–H Bonds
Chatani recently developed the Ni(II)-catalyzed arylation of aromatic amides
containing an 8-aminoquinoline as the directing group with aryl iodides as coupling
partners (Scheme 10) [34]. In this system only the 8-aminoquinoline moiety gave
the desired ortho-phenylation product. Unlike the alkylation of C–H bonds shown
in Scheme 6 [29, 30], the addition of a phosphine ligand was not required for the
reaction to proceed. The reaction showed a high efficiency with broad functional
group tolerance. The scope of the reaction is broad with regard to both aromatic
amide and coupling partner. The reaction with 1,4-diiodebenzene gave 26, in which
one of the iodides remained intact. Some heteroaromatic iodides, such as 7-iodo1H-indole and 2-iodothiophene, also participate in the arylation of C–H bonds as
coupling partners to give 27 and 28, respectively.
To gain insights into the reaction mechanism, several mechanistic experiments,
including deuterium-labeling experiments, competition experiments, radical trapping experiments, and Hammett studies, have been conducted. The results of
deuterium-labeling experiments indicated that the cleavage of C–H bonds is reversible and it does not appear to be the rate-determining step. The competition
experiments and Hammett studies indicated that the presence of an electronwithdrawing group in the aromatic amides and an electron-donating group in the
aryl iodides accelerates the reaction, suggesting that the reductive elimination step
appears to be the rate-determining step. The reaction was not completely inhibited
in the presence of the radical scavenger, 2,2,6,6-tetramethylpiperidine 1-oxyl
(TEMPO). A proposed mechanism, based on the above observations, for the
Ni-catalyzed alkylation of C–H bonds is shown in Scheme 11. The mechanism is
essentially the same as that proposed for the alkylation of C–H bonds shown in
Scheme 9 Ni-catalyzed allylation of C–H bonds with ally phosphates
Nickel-Catalyzed C–H Bond Functionalization Utilizing an N,N
27
2
)–H Bonds
Chatani recently developed the Ni(II)-catalyzed arylation of aromatic amides
containing an 8-aminoquinoline as the directing group with aryl iodides as coupling
partners (Scheme 10) [34]. In this system only the 8-aminoquinoline moiety gave
the desired ortho-phenylation product. Unlike the alkylation of C–H bonds shown
in Scheme 6 [29, 30], the addition of a phosphine ligand was not required for the
reaction to proceed. The reaction showed a high efficiency with broad functional
group tolerance. The scope of the reaction is broad with regard to both aromatic
amide and coupling partner. The reaction with 1,4-diiodebenzene gave 26, in which
one of the iodides remained intact. Some heteroaromatic iodides, such as 7-iodo1H-indole and 2-iodothiophene, also participate in the arylation of C–H bonds as
coupling partners to give 27 and 28, respectively.
To gain insights into the reaction mechanism, several mechanistic experiments,
including deuterium-labeling experiments, competition experiments, radical trapping experiments, and Hammett studies, have been conducted. The results of
deuterium-labeling experiments indicated that the cleavage of C–H bonds is reversible and it does not appear to be the rate-determining step. The competition
experiments and Hammett studies indicated that the presence of an electronwithdrawing group in the aromatic amides and an electron-donating group in the
aryl iodides accelerates the reaction, suggesting that the reductive elimination step
appears to be the rate-determining step. The reaction was not completely inhibited
in the presence of the radical scavenger, 2,2,6,6-tetramethylpiperidine 1-oxyl
(TEMPO). A proposed mechanism, based on the above observations, for the
Ni-catalyzed alkylation of C–H bonds is shown in Scheme 11. The mechanism is
essentially the same as that proposed for the alkylation of C–H bonds shown in
Scheme 9 Ni-catalyzed allylation of C–H bonds with ally phosphates
Nickel-Catalyzed C–H Bond Functionalization Utilizing an N,N
27