Organonickel

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organonickel
organonickel

Organonickel chemistry is a branch of organometallic chemistry that deals with organic compounds containing a nickel to carbon bond and their reactions [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 ever discovered was nickel tetracarbonyl Ni(CO)4 in 1890 and quickly put to use in the Mond process for nickel purification.


Overview

Organonickel compounds can have oxidation state 0 or +2 and in many ways resemble organopalladium compounds in the same Group 10 element column of the periodic table. Both metals are reducing agents: Raney nickel for nickel and a host of palladium catalysts such as palladium on carbon. Many reactions of nickel compounds are based on reductive elimination / oxidative addition sequences.

Ni alkene complexes

Bis(1,5-cyclooctadiene)nickel(0)
Bis(1,5-cyclooctadiene)nickel(0)

Many complexes exist of nickel coordinated to an alkene. In these comounds nickel is formally zerovalent Ni0 and the bonding is based on the Dewar-Chatt-Duncanson model. One widely available representative is bis(1,5-cyclooctadiene)nickel(0) or Ni(COD)2 containing two cyclooctadiene units. It is a 18VE compound with 10 electrons provided by nickel itself and 4x2 electrons more by the double bonds. This solid melts at 60°C [3] and is used as a catalyst.

Ni allyl complexes

Allyl(cyclopentadienyl)nickel(II)
Allyl(cyclopentadienyl)nickel(II)

Allyl halides react with Ni(CO)4 to form nickel pi-allyl complexes. These compounds in turn are sources of allyl nucleophiles in reaction with alkyl halides. In allyl(cyclopentadienyl)nickel(II) [4] nickel has oxidation number +2. The electron count is 18 (8 from nickel, 6 from the Cp unit and 4 more from the allyl anion).

Nickelocenes

Nickelocene
Nickelocene

The nickel metallocene pendant is nickelocene NiCp2 with +2 Ni oxidation state and with 20 valence electrons. It is easily reduced to a 19 VE nickelicinium ion. In contrast, the corresponding palladocene based on palladium is an unknown compound.

Nickel carbene complexes

With electron-rich alkenes nickel forms nickel transition metal carbene complexes containing C=Ni double bonds.

Nickel carbenes

Nickel 12 VE compounds

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

Dimesitylnickel

Organonickel Reactions

Alkene/alkyne oligomerizations

Nickel compound catalyze the oligomerization of alkenes and alkynes. This property came to light as part as the development of Ziegler-Natta catalyst in the 1950s. It was found that nickel impurities originating from an autoclave killed the propagation reaction (Aufbau) in favor of termination reaction to a terminal alkene: the polymerization of ethylene simply stopped at 1-butene. This so-called nickel effect prompted the search for other catalyst capable of this reaction during which other catalysts that actually gave high mlar mass polymers (the actual Ziegler-Natta catalysts).

One practical implementation of alkyne oligomerization is the Reppe synthesis for example in the synthesis of cyclooctatetraene:

Reppe synthesis

The oligomerization of butadiene with ethylene to trans-1,4-hexadiene at one time was an industrial process.

The formation of organonickel compounds in this type of reaction is not always obvious but in a carefully designed experiment two such intermediates were formed quantitatively [5] [6]:

Reaction of N-(benzenesulfonyl)benzaldimine with two equivalents of diphenylacetylene


Coupling reactions

Nickel compounds cause the coupling reaction between allyl and aryl halides. Other coupling reactions involving nickel in catalytic amounts are the Kumada coupling and the Negishi coupling.

Coupling of 3-Chloro-2-methyl-1-propene to 2,5-dimethyl-1,6-hexadiene

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.

Nickel catalyzed carbonylation of acetylene to acrylic acid

See also

  • Compounds of carbon with other elements in the periodic table:

Template:ChemicalBondsToCarbon

References

  1. F.A. Carey R.J. Sundberg Advanced Organic Chemistry 2nd Ed. ISBN 0306411997
  2. Comprehensive organometallic chemistry III Robert Crabtree, Mike Mingos 2006 ISBN: 0-08-044590-X
  3. http://www.sigmaaldrich.com/catalog/search/ProductDetail/ALDRICH/244988
  4. http://www.sigmaaldrich.com/catalog/search/ProductDetail/ALDRICH/524271
  5. Formation of an Aza-nickelacycle by Reaction of an Imine and an Alkyne with Nickel(0): Oxidative Cyclization, Insertion, and Reductive Elimination Sensuke Ogoshi Haruo Ikeda, and Hideo Kurosawa Angew. Chem. Int. Ed. 2007, 46, 4930 –4932Error: Bad DOI specified!
  6. Reaction of the imine N-(benzenesulfonyl)benzaldimine with two equivalents of diphenylacetylene with NiCOD2 and tricyclohexylphosphine first to nickelapyrroline and with a second insertion a nickeldihydroazepine and finally on heating a dihydropyridine

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