ca01 only detailed ToC 1..24

32 Science of Synthesis 1.1 Organometallic Complexes of Nickel
Bis(ç 4 -cycloocta-1,5-diene)nickel(0) (2): [13]
A 250-mL Schlenk flask equipped with a stirring bar and a pressure-equalizing addition
funnel was charged with technical grade [Ni(acac) 2](1; 4.67 g, 0.0182 mol, 1.00 equiv) and
briefly dried under vacuum with a heat gun. After cooling and establishing a positive N 2
atmosphere, the solid was suspended in THF (25 mL) and treated with cycloocta-1,5-diene
(7.93 g, 0.0723 mol, 4.00 equiv). The suspension was cooled to –78 8C with a dry ice/acetone
bath to give a green slurry. A 1.0 M soln of DIBAL-H in THF (45.4 mL, 0.0454 mol,
2.50 equiv) was transferred to the addition funnel under N 2 via a cannula. The DIBAL-H
soln was added over 1 h to give a dark, reddish-brown soln which was allowed to warm
to 0 8C over a 1 h period. The soln was treated with Et 2O (65 mL) to give a light yellow precipitate.
The suspension was cooled to –788C and allowed to stand for 12 h to complete
precipitation. The solid product was isolated by filtration at –788C via a filter paper tipped
cannula, washed with cold Et 2O (15 mL portions) until the brown residues were removed,
and dried in vacuo. [Ni(cod) 2](2) was obtained as a pale yellow powder and was suitable for
immediate use; yield: 3.2 g (72%).
The material may be recrystallized by the following procedure. In a glovebox, crude
[Ni(cod) 2] (3.2 g) was dissolved in a minimum volume of toluene (25 mL • g –1 )at258C and
rapidly filtered through Celite to remove metallic nickel. The deep yellow soln was allowed
to stand at –788C for 12 h to give bright yellow-orange needles. Removal of the supernatant
at –788C through a filter paper tipped cannula, followed by a pentane wash
(2 ” 15 mL), gave pure material; yield: 1.28g (40%).
Dichlorobis(triphenylphosphine)nickel(II) (3): [14]
A soln of NiCl 2 •6H 2O (2.38g, 0.01 mol) in H 2O (2 mL) was diluted with glacial AcOH
(50 mL), and Ph 3P (5.25 g, 0.02 mol) in glacial AcOH (25 mL) was added. The olive-green microcrystalline
precipitate, when kept in contact with its mother liquor for 24 h, gave dark
blue crystals which were filtered off, washed with glacial AcOH, and dried in a vacuum
desiccator (H 2SO 4, KOH); yield: 3.81 g (84%).
1.1.1 Product Subclass 1:
Nickel Complexes of 1,3-Dienes
Nickel complexes with 1,3-dienes are important intermediates in a variety of catalytic
processes. In contrast to many classes of metal–diene complexes, such as those of iron
and palladium in which metal complexation activates the ð-system towards nucleophilic
attack, (ç 4 -diene)nickel complexes are most useful in cycloaddition processes and in couplings
to polar ð-systems such as carbonyls. Few examples of diene–nickel complexes are
structurally well characterized, but they are commonly invoked in the mechanisms of
many synthetic procedures.
Synthesis of Product Subclass 1
1.1.1.1 Method 1:
Ligand Exchange with Bis(ç 4 -cycloocta-1,5-diene)nickel(0)
The high reactivity of nickel–diene complexes, which renders them very useful in catalytic
applications, makes their isolation quite difficult in most cases. The few cases in which
nickel–1,3-diene complexes (e.g., 4) have been isolated generally involve displacement of
a ligand with a low binding constant such as cyclooctadiene. This should, in theory, be
possible using nickel(II) salts reduced in situ, although bis(ç 4 -cycloocta-1,5-diene)nickel(0)
or (ç 6 -cyclododeca-1,5,9-triene)nickel(0) (Scheme 3; cdt = cyclododeca-1,5,9-triene) are typically
employed. [15]