ca01 only detailed ToC 1..24

1.1.4 Nickel–Alkene Complexes 63
Bis(methyl acrylate)(pyridine)nickel(0) (69): [112]
To NiCl 2 •6H 2O (4.7 g, 20 mmol), methyl acrylate (5.0 mL, 55 mmol), and pyridine (5.0 mL,
61 mmol) in THF (50 mL) was added Zn powder (5.0 g, 76 mmol). The suspension was heated
to 608C, and the oil bath was removed. After 2 h the mixture was filtered, and the solid
residue was washed with THF (3 ” 15 mL). After removal of the solvent in vacuo, extraction
with Et 2O (50 mL) left behind the insoluble zinc salts. Filtration and evaporation of
the extract in vacuo gave a red oil which was treated with hexane to dissolve the excess
pyridine and methyl acrylate. The hexane layer was discarded, and the residual oil was
dissolved in Et 2O (50 mL). Cooling to –188C afforded 69 as a pale orange powder; yield:
4.3 g (70%); mp 808C (dec).
Applications of Product Subclass 4 in Organic Synthesis
1.1.4.2 Method 2:
Conjugate Addition to Electrophilic Double Bonds
Nickel-catalyzed conjugate additions are among the most widely used synthetic applications
of nickel chemistry. Conjugate additions of a broad range of main-group and transition-metal
organometallics have been reported to be accelerated by nickel catalysis.
Bis(acetylacetonato)nickel(II) (1) is the most widely used catalyst due to its low cost and
air stability, although bis(ç 4 -cycloocta-1,5-diene)nickel(0) (2) is an excellent catalyst for
most conjugate additions. Bis(acetylacetonato)nickel(II) (1) may be reduced by the nucleophilic
organometallic reagent (organozinc, organoaluminum, etc.), or more typically it
may be reduced with diisobutylaluminum hydride prior to treatment with the nucleophilic
organometallic reagent. The primary advantages of nickel-catalyzed conjugate additions
relative to organocuprates are increased thermal stability of the reagents and increased
efficiency with sterically hindered substrates. Several asymmetric variants have
been reported, but no general solution to the problem of asymmetric catalysis has been
reported. The four variations listed below have received the most attention, although additions
of triorganoindiums, [115] alkenylboranes, [116] and organotitaniums [117] have been reported.
Mackenzie has reported a related procedure with organotins that likely bears
mechanistic similarity to the procedures described here. [39] However, since this reaction
class was demonstrated to involve nickel–ð-allyl complexes, its description is included
in Section 1.1.2.7.2. It is worth noting that the variations described below may possibly
involve ð-allyl complexes as reactive intermediates in direct analogy to the model proposed
by Mackenzie. A comprehensive review of nickel-catalyzed nucleophilic additions
to activated alkenes has appeared. [186]
1.1.4.2.1 Variation1:
Organoaluminums
The bis(acetylacetonato)nickel(II)-catalyzed addition of trimethylaluminum was the firstreported
variant of nickel-catalyzed conjugate additions, [118,119] and a later report demonstrated
that the process is efficient with sterically demanding substrates such as 70 that
possess â,â-disubstituted enones (Scheme 57). [120] Significantly, alkynylaluminum reagents
efficiently transfer the alkynyl unit in a conjugate fashion to enones such as 71
(Scheme 57). [121,122] This transformation is notoriously difficult with organocopper chemistry.
Therefore, the nickel-catalyzed procedure is exceptionally useful.
for references see p 79