Organonickel chemistry

Organonickel chemistry is a branch of organometallic chemistry that deals with organic compounds featuring nickel-carbon bonds.^[1][2] They are used as a catalyst, as a building block in organic chemistry and in chemical vapor deposition. Organonickel compounds are also short-lived intermediates in organic reactions. The first organonickel compound was nickel tetracarbonyl Ni(CO)₄, reported in 1890 and quickly applied in the Mond process for nickel purification. Organonickel complexes are prominent in numerous industrial processes including carbonylations, hydrocyanation, and the Shell higher olefin process.^[3][4]

Classes of compounds

Alkyl and aryl complexes

A popular reagent is Ni(CH₃)₂(tetramethylethylenediamine).^[5]

Many alkyl and aryl complexes are known with the formula NiR(X)L₂. Examples include [(dppf)Ni(cinnamyl)Cl)], trans-(PCy₂Ph)₂Ni(o-tolyl)Cl]], (dppf)Ni(o-tolyl)Cl]], (TMEDA)Ni(o-tolyl)Cl, and (TMEDA)NiMe₂.

Nickel compounds of the type NiR₂ also exist with just 12 valence electrons. In solution however solvent always interact with the metal atom increasing the electron count. One 12 VE compound is di(mesityl)nickel prepared from (allyl)₂Ni₂Br₂ and the corresponding Grignard reagent.

(allyl)₂Ni₂Br₂ + 4 C₆H₂Me₃MgBr → 2 (allyl)MgBr + 2 MgBr₂ + 2 (C₆H₂Me₃)₂Ni

Alkene complexes

Many complexes exist of nickel coordinated to an

and as a precursor for many other nickel compounds.

Allyl complexes

Nickel forms several simple

.

Cyclopentadienyl complexes

Nickelocene NiCp₂ with +2 Ni oxidation state and 20 valence electrons is the main metallocene of nickel. It can be oxidized by one electron. The corresponding palladocene and platinocene are unknown. From nickelocene, many derivatives are generated, e.g. CpNiLCl, CpNiNO, and Cp₂Ni₂(CO)₃.

Carbene complexes

Nickel forms carbene complexes, formally featuring C=Ni double bonds.^[9]

Reactions

Alkene/alkyne oligomerizations

Nickel compounds catalyze the

. This so-called nickel effect prompted the search for other catalysts capable of this reaction, with results in the finding of new catalysts that technically produced high molar mass polymers, like the modern Ziegler–Natta catalysts.

One practical implementation of alkyne oligomerization is the

:

This is a formal [2+2+2+2]cycloaddition. The oligomerization of butadiene with ethylene to trans-1,4-hexadiene was an industrial process at one time.

Formal [2+2+2]cycloadditions also take place in

derivative.

In the

liberates the tetrahydroanthracene compound.

The formation of organonickel compounds in this type of reaction is not always obvious but in a carefully designed experiment two such intermediates are formed quantitatively:[11]^[12]

It is noted in one study

7 isomers are possibly differing in the position of the substituents or the double bond positions. One strategy to remedy this problem employs certain diynes:

The selected reaction conditions also minimize the amount formed of competing [2+2+2]cycloaddition product to the corresponding substituted arene.

Coupling reactions

Nickel compounds cause the

.

Ni carbonylation

Ni catalyzes the addition of carbon monoxide to alkenes and alkynes. The industrial production of acrylic acid at one time consisted of combining acetylene, carbon monoxide and water at 40-55 atm and 160-200 °C with nickel(II) bromide and a copper halide.

See also

• Nickel(IV) organometallic complex
• Nickel(II) precatalysts
• Lactate racemase

Further reading

• P.W. Jolly, G. Wilke, ed. (1974). The Organic Chemistry of Nickel Volume I: Organonickel Complexes. Academic Press.
  ISBN 9780123884015
  .

References