ca01 only detailed ToC 1..24

40 Science of Synthesis 1.1 Organometallic Complexes of Nickel
then transferred by cannula onto the [Ni(cod) 2]. The resulting purple-red slurry was stirred
for 10 min and then treated with TMSCl (462 ìL, 3.64 mmol, 2.00 equiv) to afford a deep
red soln. After 45 min, the volatiles were removed at 0.1 Torr to obtain an orange-red powder.
This was extracted with pentane (20 mL) through a filter paper tipped cannula. The
clear red filtrate was concentrated under vacuum to ca. 5 mL and then cooled to –208C for
24 h to induce crystallization. The precipitate was isolated by removal of the supernatant
through a filter paper tipped cannula while maintaining the mixture at –208C, and
washed with pentane (2 ” 3 mL) to afford 25 as a burgundy-red crystalline solid; yield:
0.35 g (86%).
[(1,2,3-ç)-1-(tert-Butyldimethylsiloxy)cyclopentenyl]chlorobis(pyridine)nickel(II) (27): [38]
A 100-mL Schlenk tube equipped with a magnetic stirring bar and rubber septum was
charged with [NiCl 2(py) 4](26; 10.0 g, 22.4 mmol, 1.00 equiv) and evacuated and refilled
with N 2 twice to establish an inert atmosphere. THF (40 mL) was added, followed by cycloocta-1,5-diene
(8.20 mL, 67.2 mmol, 3.00 equiv), and the resulting mixture was cooled to
0 8C. A second 100-mL Schlenk tube containing Na metal strips (1.03 g, 44.8mmol,
2.00 equiv; each ca. 2 cm ” 0.4 cm ” 0.1 cm) was connected to this flask with a flexible
adapter (available from Aldrich) under a rapid flow of N 2 (an inert atmosphere having previously
been established in the second Schlenk tube and adapter by capping the free end
of the adapter and evacuating and refilling with N 2). The Na strips were then transferred
to the stirred 0–5 8C mixture in four portions over 1.5 h to give, after an additional 40 min at
0–5 8C, a very dark brown (but not black) supernatant, a small amount of precipitated yellow
[Ni(cod) 2], and no apparent blue [NiCl 2(py) 4]. This was treated with a soln of cyclopent-2enone
(1.88mL, 22.4 mmol, 1.00 equiv) and TBDMSCl (3.38g, 22.4 mmol, 1.00 equiv) in THF
(15 mL) and stirred at 258C for 30 min to afford an orange mixture. The soln of 27 thus obtained
was directly used in coupling reactions; no purification or yield was reported.
1.1.2.4 Method 4:
Oxidative Cyclization of Nickel(0) Complexes of Conjugated Dienes
ð-Allyl complexes are commonly invoked as intermediates in the reactions of (ç 4 -diene)nickel
complexes. If a nickel(0) complex possesses both a conjugated diene ligand and another
ð-bound ligand, an oxidative cyclization may occur to form a ð-allyl ligand within a
nickel(II) metallacycle. Much of the [4+4]- and [4 +2]-cycloaddition chemistry described
for ç 4 -diene complexes probably involves the intermediacy of nickel metallacycles that
possess a ç 3 -allyl ligand. Oxidative cyclizations of this type are also useful in the stoichiometric
preparation of nickel–ð-allyl complexes. The spectator ligand properties play a significant
role in determining the position of the equilibrium for oxidative cyclization–reductive
cleavage processes (Scheme 15). [40]
Scheme 15 Ligand Dependence in the Formation of ð-Allyl Complexes by
Oxidative Cyclization [40]
CO2Me + Ni(cod)2 + Ph3P
MeO2C
Ph3P Ni
2
MeO2C CO 2Me
+ Ni(cod) 2 + bipy
2
MeO2C
MeO 2C
Ni(bipy)