C O M M U N I C A T I O N S
Table 2. Ni/2-Catalyzed Arylation of Aryl Polyfluorides and
Trichlorobenzene required refluxing conditions (in ether; the use
of THF slowed the conversion) to give the sterically hindered 1,2-
diphenyl substitution (entry 7). In a similar vein, we consider that
steric effect causes selective production of 1,3-diphenylated com-
pound in entry 8. Even the 1,2,4,5-tetraphenylation could be
achieved, albeit in moderate yield (entry 9).
Polychloridesa
In summary, we have designed a new bidentate ligand 2 on the
basis of an assumption that the C-F bond cleavage is a turnover-
limiting step of the nickel-catalyzed reaction of aryl fluorides, and
hence, the bimetallic synergy accelerates the reaction. Though the
reported synthetic results do not necessarily prove this hypothesis,
the high reactivity and the chemoselectivity, in particular, are con-
sistent with the assumption. Probing the generality of the hypothesis
will be the next step of our study. The new catalytic system does
not accelerate the equivalent palladium-catalyzed reaction between
Grignard and arylating reagents, suggesting that the turnover-
limiting step is different in the palladium catalysis. In addition to
its synthetic merit, the high reactivity of the new catalytic system
may suggest new ways to scavenge environmentally noxious poly-
chloro aromatics. Though the ligand 2 was employed here as its
racemate, we consider that its optically active counterpart would
be worthwhile to examine in the future.
a The reaction was carried out at 0.5-1 mmol scale at room temperature
unless otherwise noted. b Isolated yield. c The reaction temperature was 45
°C (bath temp). d The rest of the product consisted of ca. 2:3 mixture of
1-chloro-2,4,5-triphenylbenzene and 1,2,4-triphenylbenzene.
phenyl (homocoupling of the sulfide, 16%) and toluene (reduction,
10%). Thus, the reaction was found to become faster in an order
of X ) SMe < OTf < F < Cl < Br < I.
Supporting Information Available: Experimental and computa-
tional details, and full citation of ref 9 (PDF). This material is available
Competition experiments were carried out. The reaction of an
equimolar mixture of 4-fluorotoluene, 1-ethyl-4-propylthiobenzene,
and PhMgBr in the presence of 2 afforded 4-methylbiphenyl (60%)
and none of 4-ethylbiphenyl (the aryl sulfide was entirely recovered)
(eq 2), while the same reaction in the presence of dppp gave more
of the latter than the former. Interestingly, the Ni/2-catalyzed
reaction was much slower in the presence of the sulfide than in its
absence (Table 1, entry 1), suggesting that the sulfide is a preferred
ligand to the catalyst but does not take part in the coupling reaction.
References
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The reaction with vinyl chlorides and bromides was efficient
and requires less than 0.05 mol % catalysis (entries 17 and 18),
while reaction with enol triflates was sluggish (entry 19) and
required 1 mol % of catalyst to achieve 88% yield after 5 h.
Electron-deficient (entry 7), electron-rich (entries 8-10), and
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smoothly (entries 4 and 5). The methoxy group in 2,4,6-trichloro-
anisole remained intact in the triarylation reaction (entry 6). 1,2,4-
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