Nickel Hydroxo Complexes as Intermediates in Nickel-Catalyzed Suzuki–Miyaura Cross-Coupling

The
synthesis, characterization, and reactivity of intermediates
formed in the Ni-catalyzed Suzuki–Miyaura cross-coupling (SMC)
of an aryl chloride are described. Oxidative addition of 1-chloro-4-trifluoromethylbenzene
(1) to a mixture of Ni­(cod)2 and PCy3 afforded NiCl­(4-CF3Ph)­(PCy3)2 (2), which then cleanly provided dimeric [Ni­(4-CF3Ph)­(μ–OH)­(PCy3)]2 (3) by reaction with aqueous KOH. Reactivity studies of 2 and 3 with phenylboronic acid (4) revealed
that, while 2 affords only traces of the biphenyl coupling
product after 24 h, the same reaction with 3 is complete
within minutes at room temperature. In contrast, the reaction of 3 with potassium phenyltrihydroxyborate (6) is
much slower than that with boronic acid 4, and significantly
lower yields of the cross-coupling product are obtained. We show that
formation of the hydroxo species 3 is the rate-determining
step in the present SMC.