Paper
RSC Advances
using commercial phenylmagnesium bromide as the starting more hindered ancillary ligands. The effect presumably arises
material in the presence of air (entry 12). To our surprise the from a relief in steric congestion upon generation of the free
yield was lower (37%). This may be due to the difficulty in organic product and a resulting metal center with a reduced
handling the commercial phenylmagnesium bromide.10 Most of coordination number.32
the reported Grignard reagent based catalytic systems5,8 require
a sophisticated set-up to handle the reagents in a moisture free
environment in contrast to the present work.
4. Conclusions
This encouraging result led us to extend the scope of the
reaction to various aryl Grignard reagents to synthesize simple
In conclusion, we have developed an energy efficient nickel-
catalyzed coupling methodology to couple aryl Grignard
functionalized biaryls in good yield (Table 2). It was observed
reagents at room temperature, using atmospheric oxygen as the
that under similar reaction conditions high yields of 2a and 2b
oxidant. The reaction system is compatible with diverse func-
tionality to afford biaryls in good to excellent yields. It is note-
worthy that the reaction is chemoselective. The in situ
preparation of the Grignard reagent, small amount of catalyst
were obtained upon efficient coupling of 4-methoxy- and
2-methoxyphenylmagnesium bromide, respectively (entries
1 and 2). The presence of a methyl group at the ortho-position of
the aryl Grignard reagent resulted in a somewhat lower yield of
loading, and mild reaction conditions, make this catalytic
the homocoupling product (entry 4). It is noteworthy that the
methodology practicable to the large scale synthesis of
present reaction system is tolerant of an aryl chloride (entry 6).
symmetrical biaryls.
Nitro and nitrile groups were tolerated (entries 7 and 8), hence
the reaction is chemoselective. Although, the sterically
demanding substrate 1i required a higher reaction temperature
Acknowledgements
and longer reaction time, it gave the corresponding biaryl 2i in
Mrs Aparna P. I. Bhat thanks National Institute of Technology
moderate to good yield (entry 9). Also, the reaction allows the
Karnataka, Surathkal for a research fellowship. The authors
thank Indian Institute of Science, Bangalore, for NMR analysis.
coupling of heteroaryl Grignard reagent 1j successfully (entry
10). It was observed that when a Grignard reagent contains an
electron donating group it enhances the yield of the coupling
product compared to a reagent with an electron withdrawing
group. The formation of cross-coupling products was found to
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RSC Adv., 2013, 3, 22191–22198 | 22197