Organonickel chemistry is a branch of organometallic chemistry that deals with organic compounds feature nickel-carbon bonds. 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 put to use in the Mond process for nickel purification. Organonickel complexes are prominent in numerous industrial processes including carbonylations, hydrocyanation, and the Shell higher olefin process.
Organonickel compounds adopts oxidation state 0 or +2. The resemblance to organopalladium compounds is not strong, although both metals undergo reactions that involve sequences of reductive elimination and oxidative addition reactions.
Ni alkene complexes 
Many complexes exist of nickel coordinated to an alkene. In these compounds nickel is formally zerovalent Ni0 and the bonding is described with the Dewar-Chatt-Duncanson model. One common representative is Bis(cyclooctadiene)nickel(0) (Ni(COD)2), which contains two cyclooctadiene ligands. It is a 18VE compound with 10 electrons provided by nickel itself and 4x2 electrons more by the double bonds. This solid, which melts at 60 °C, is used as a catalyst and as a precursor for many other nickel compounds.
Ni allyl complexes 
Allyl halides react with Ni(CO)4 to form pi-allyl complexes, (allyl)2Ni2Cl2. These compounds in turn are sources of allyl nucleophiles. In (allyl)2Ni2Cl2 and (allyl)Ni(C5H5), nickel is assigned to oxidation number +2, and the electron counts are 16 and 18, respectively.
Nickel carbene complexes 
Nickel forms carbene complexes, formally featuring C=Ni double bonds.
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)2Ni2Br2 and the corresponding Grignard reagent.
Alkene/alkyne oligomerizations 
Nickel compounds 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 which resulted in the discovery of new catalysts that actually gave high molar mass polymers (the actual Ziegler-Natta catalysts).
Formal [2+2+2]cycloadditions also take place in alkyne trimerisation. This trimerisation can be extended to inclusion of benzyne. Benzyne is generated in situ from a benzene compound with a triflate and a trimethylsilyl substituent in the ortho- positions and reacts with a di-yne such as 1,7-octadiyne and with a nickel(II) bromide / zinc catalyst system (NiBr2 bis(diphenylphosphino) ethane / Zn) to the corresponding naphthalene derivative.
In the catalytic cycle elementary zinc serves to reduce nickel(II) to nickel(0) to which can then coordinate two alkyne bonds. A cyclometalation step follows to the nickelcyclopentadiene intermediate and then coordination of the benzyne which gives a C-H insertion reaction to the nickelcycloheptatriene compound. Reductive elimination liberates the tetrahydroanthracene compound.
It is noted in one study  that this reaction only works with acetylene itself or with simple alkynes due to poor regioselectivity. From a terminal alkyne 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 
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 
- Compounds of carbon with other elements in the periodic table:
|Core organic chemistry||Many uses in chemistry|
|Academic research, but no widespread use||Bond unknown|
- F.A. Carey R.J. Sundberg Advanced Organic Chemistry 2nd Ed. ISBN 0-306-41199-7
- Comprehensive organometallic chemistry III Robert Crabtree, Mike Mingos 2006 ISBN 0-08-044590-X
- 244988 Bis 1 5 cyclooctadiene nickel 0
- Martin F. Semmelhack and Paul M. Helquist (1988), "Reaction of Aryl Halides with π-Allylnickel Halides: Methallylbenzene", Org. Synth. 52: 115; Coll. Vol. 6: 161
- Jen-Chieh Hsieh and Chien-Hong Cheng (2005). "Nickel-catalyzed cocyclotrimerization of arynes with diynes; a novel method for synthesis of naphthalene derivatives". Chemical Communications 2005 (19): 2459–2461. doi:10.1039/b415691a.
- 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 –4932 doi: 10.1002/anie.200700688
- 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
- Nickel(0)-Catalyzed [2 + 2 + 2 + 2] Cycloadditions of Terminal Diynes for the Synthesis of Substituted Cyclooctatetraenes Paul A. Wender and Justin P. Christy J. Am. Chem. Soc.; 2007; 129(44) pp 13402 - 13403; (Communication) doi:10.1021/ja0763044