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1.1 Organometallic Complexes of Nickel

DOI: 10.1055/sos-SD-001-00002

Montgomery, J.Science of Synthesis, (2001111.

General Introduction

This contribution provides an overview of contemporary synthetic methods of broad applicability that involve the preparation and use of nickel π-complexes as starting materials or reactive intermediates. Numerous excellent reviews on the chemistry of nickel have appeared that are complementary to this contribution in subject and scope. An outstanding review by Chetcuti describes the known π-complexes of nickel,[‌1‌] and several other structural classes of nickel complexes have been reviewed;[‌2‌‌4‌] σ-bonded organonickel compounds are reviewed in HoubenWeyl, Vol.13/9b, pp632700. The historical development and early applications of nickel chemistry have been reviewed by Wilke[‌5‌] and Jolly,[‌6‌] industrial applications have been reviewed by Keim,[‌7‌] and several other reviews on specific groups of synthetic transformations have appeared.[‌8‌‌12‌,‌187‌] The organometallic chemistry of nickel has a rich history dating back more than 100 years.[‌5‌] Despite its long history, fundamentally new reactions are still being developed at a rapid pace. Furthermore, existing reactions are being applied in new and creative ways to solve long-standing challenges in organic synthesis. More and more of the synthetic organic community is beginning to realize that nickel catalysis provides preparatively convenient reactions of broad scope in a variety of contexts. In many cases, the reactivity exhibited by nickel may not be achieved by any other transition element. At this time, organonickel chemistry seems to be well poised to provide an increasing number of new reactions and interesting mechanistic questions, as well as to gain an increasingly important role in the organic chemist's repertoire of mainstream synthetic transformations.

The most commonly employed catalysts in nickel-catalyzed reactions are bis(acetylacetonato)nickel(II) (1), which is commercially available, bis(η4-cycloocta-1,5-diene)nickel(0) (2) which is also commercially available or may be easily prepared (Scheme 1),[‌13‌] and dichlorobis(triphenylphosphine)nickel(II) (3) which can also be easily prepared (Scheme 2).[‌14‌]

Safety

SAFETY: Tetracarbonylnickel(0) should be handled with extreme caution due to its volatility and high toxicity. All nickel compounds should be handled with care since many are cancer suspect agents.[‌188‌]

Scheme 1 Synthesis of Bis(η4-cycloocta-1,5-diene)nickel(0)[‌13‌]

Scheme 2 Synthesis of Dichlorobis(triphenylphosphine)nickel(II)[‌14‌]

Experimental Procedure

Bis(η4-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; 4.67g, 0.0182mol, 1.00equiv) and briefly dried under vacuum with a heat gun. After cooling and establishing a positive N2 atmosphere, the solid was suspended in THF (25mL) and treated with cycloocta-1,5-diene (7.93g, 0.0723mol, 4.00equiv). The suspension was cooled to 78°C with a dry ice/acetone bath to give a green slurry. A 1.0M soln of DIBAL-H in THF (45.4mL, 0.0454mol, 2.50equiv) was transferred to the addition funnel under N2 via a cannula. The DIBAL-H soln was added over 1h to give a dark, reddish-brown soln which was allowed to warm to 0°C over a 1h period. The soln was treated with Et2O (65mL) to give a light yellow precipitate. The suspension was cooled to 78°C and allowed to stand for 12h to complete precipitation. The solid product was isolated by filtration at 78°C via a filter paper tipped cannula, washed with cold Et2O (15mL 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: 3.2g (72%).

The material may be recrystallized by the following procedure. In a glovebox, crude [Ni(cod)2] (3.2g) was dissolved in a minimum volume of toluene (25mL·g1) at 25°C and rapidly filtered through Celite to remove metallic nickel. The deep yellow soln was allowed to stand at 78°C for 12h to give bright yellow-orange needles. Removal of the supernatant at 78°C through a filter paper tipped cannula, followed by a pentane wash (2×15mL), gave pure material; yield: 1.28g (40%).

Dichlorobis(triphenylphosphine)nickel(II) (3):[‌14‌]

A soln of NiCl26H2O (2.38g, 0.01mol) in H2O (2mL) was diluted with glacial AcOH (50mL), and Ph3P (5.25g, 0.02mol) in glacial AcOH (25mL) was added. The olive-green microcrystalline precipitate, when kept in contact with its mother liquor for 24h, gave dark blue crystals which were filtered off, washed with glacial AcOH, and dried in a vacuum desiccator (H2SO4, KOH); yield: 3.81g (84%).

References