Adholeya et al. showcased a magnetically recoverable, silica-based nickel
catalyst, Ni-TC@ASMNPs, that could be used to catalyze Suzuki-Miyaura crosscoupling reactions [32]. The NPs were prepared via co-precipitation; iron salts
were initially combined with ammonium hydroxide. Then, a coating of silica
was applied in order to inhibit the aggregation of the NPs. The silica-coated
NPs were then further functionalized with an NH 2 linker to provide the solid
support. Finally, the material was stirred in a solution of NiCl 2 •6H 2 O to form the
Ni NPs which were easily separated using a magnet. Their analysis by TEM
indicated an average diameter of 10–12 nm.
Upon optimization of these couplings, it was found that dioxane was the preferred
solvent. K 3 PO 4 was utilized as base, being far superior to other bases tested.
Reaction temperatures lower than 100
C led to longer reaction times. The presence
of PPh 3 was essential, as no reaction occurred in the absence of this ligand.
It was postulated that the ligand may be stabilizing Ni(0) prior to oxidative addition.
A range of aryl halides and pseudo-halides (Br, Cl, I, OTs) were all amenable to
this transformation (Fig. 14). Aryl bromides were able to smoothly couple in goodto-excellent yields regardless of the electronic properties of the ring. Due to the
magnetic properties of the NPs, the nickel catalyst could be cleanly separated
from the reaction mixture using a permanent magnet. The same catalyst could
be recycled for six subsequent reactions without noticeable loss of activity, as
well as with negligible leaching of nickel.
Preparation of Catalyst Ni-TC@ASMNPs Fe 2 (SO 4 ) 3 (6.0 g) and FeSO 4 (4.2 g)
were dissolved in 250 mL of water and stirred at 60
C to give a yellowish
orange solution. NH 4 OH solution (25%, 15 mL) was added into the solution with
vigorous stirring, and the color of the bulk solution turned black. Stirring was
continued for another 30 min, and the precipitated MNPs were separated using
an external magnet and washed several times with deionized water and ethanol.
Fig. 14 Nickel-catalyzed Suzuki-Miyaura cross-couplings
92
M. Cortes-Clerget et al.
catalyst, Ni-TC@ASMNPs, that could be used to catalyze Suzuki-Miyaura crosscoupling reactions [32]. The NPs were prepared via co-precipitation; iron salts
were initially combined with ammonium hydroxide. Then, a coating of silica
was applied in order to inhibit the aggregation of the NPs. The silica-coated
NPs were then further functionalized with an NH 2 linker to provide the solid
support. Finally, the material was stirred in a solution of NiCl 2 •6H 2 O to form the
Ni NPs which were easily separated using a magnet. Their analysis by TEM
indicated an average diameter of 10–12 nm.
Upon optimization of these couplings, it was found that dioxane was the preferred
solvent. K 3 PO 4 was utilized as base, being far superior to other bases tested.
Reaction temperatures lower than 100
C led to longer reaction times. The presence
of PPh 3 was essential, as no reaction occurred in the absence of this ligand.
It was postulated that the ligand may be stabilizing Ni(0) prior to oxidative addition.
A range of aryl halides and pseudo-halides (Br, Cl, I, OTs) were all amenable to
this transformation (Fig. 14). Aryl bromides were able to smoothly couple in goodto-excellent yields regardless of the electronic properties of the ring. Due to the
magnetic properties of the NPs, the nickel catalyst could be cleanly separated
from the reaction mixture using a permanent magnet. The same catalyst could
be recycled for six subsequent reactions without noticeable loss of activity, as
well as with negligible leaching of nickel.
Preparation of Catalyst Ni-TC@ASMNPs Fe 2 (SO 4 ) 3 (6.0 g) and FeSO 4 (4.2 g)
were dissolved in 250 mL of water and stirred at 60
C to give a yellowish
orange solution. NH 4 OH solution (25%, 15 mL) was added into the solution with
vigorous stirring, and the color of the bulk solution turned black. Stirring was
continued for another 30 min, and the precipitated MNPs were separated using
an external magnet and washed several times with deionized water and ethanol.
Fig. 14 Nickel-catalyzed Suzuki-Miyaura cross-couplings
92
M. Cortes-Clerget et al.