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[[File:Organonickel.png|right|150px|organonickel]]'''Organonickel chemistry''' is a branch of organometallic chemistry that deals with organic compounds featuring nickel-carbon bonds.<ref>F.A. Carey R.J. Sundberg ''Advanced Organic Chemistry'' 2nd Ed. {{ISBN|0-306-41199-7}}</ref><ref>''Comprehensive organometallic chemistry'' III Robert Crabtree, Mike Mingos 2006  {{ISBN|0-08-044590-X}}</ref> 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)<sub>4</sub>, 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 [[Chemistry:Shell higher olefin process|Shell higher olefin process]].<ref>{{cite journal |doi=10.1021/acscatal.5b00072|title=Nickel: The "Spirited Horse" of Transition Metal Catalysis|year=2015|last1=Ananikov|first1=Valentine P.|journal=ACS Catalysis|volume=5|issue=3|pages=1964–1971}}</ref>
== Classes of compounds ==

:[[File:Ni(cod)2.png|right|200px|Bis(1,5-cyclooctadiene)nickel(0)]]
===Alkyl and aryl complexes===
A popular reagent is Ni(CH<sub>3</sub>)<sub>2</sub>(tetramethylethylenediamine).<ref>{{cite journal |doi=10.1021/acs.organomet.0c00500|title=A Practical Synthesis of &#91;(tmeda)Ni(CH<sub>3</sub>)<sub>2</sub>&#93;, Isotopically Labeled &#91;(tmeda)Ni(<sup>13</sup>CH<sub>3</sub>)<sub>2</sub>&#93;, and Neutral Chelated-Nickel Methyl Complexes|year=2020|last1=Göttker-Schnetmann|first1=Inigo|last2=Mecking|first2=Stefan|journal=Organometallics|volume=39|issue=18|pages=3433–3440}}</ref>

Many alkyl and aryl complexes are known with the formula NiR(X)L<sub>2</sub>.  Examples include [(dppf)Ni(cinnamyl)Cl)], ''trans''-(PCy<sub>2</sub>Ph)<sub>2</sub>Ni(''o''-tolyl)Cl]], (dppf)Ni(''o''-tolyl)Cl]], (TMEDA)Ni(''o''-tolyl)Cl, and (TMEDA)NiMe<sub>2</sub>.
[[File:Doyle reduction.tif|center|350x350px|thumb|Synthesis of [(TMEDA)Ni(''o''-tolyl)Cl].<ref name=":1">{{Cite journal |last1=Shields |first1=Jason D. |last2=Gray |first2=Erin E. |last3=Doyle |first3=Abigail G. |date=2015-05-01 |title=A Modular, Air-Stable Nickel Precatalyst |journal=Organic Letters |volume=17 |issue=9 |pages=2166–2169 |doi=10.1021/acs.orglett.5b00766 |pmc=4719147 |pmid=25886092}}</ref>]]

Nickel compounds of the type NiR<sub>2</sub> 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)<sub>2</sub>Ni<sub>2</sub>Br<sub>2</sub> and the corresponding [[Chemistry:Grignard reagent|Grignard reagent]].
:(allyl)<sub>2</sub>Ni<sub>2</sub>Br<sub>2</sub>  +   4 C<sub>6</sub>H<sub>2</sub>Me<sub>3</sub>MgBr   →   2 (allyl)MgBr  + 2 MgBr<sub>2</sub>  +  2 (C<sub>6</sub>H<sub>2</sub>Me<sub>3</sub>)<sub>2</sub>Ni

===Alkene complexes===
Many complexes exist of nickel coordinated to an [[Chemistry:Alkene|alkene]]. Practical applications of this theme include polymerization or oligomerization of alkenes, as in the Shell Higher Olefin Process.<ref>{{cite journal |doi=10.1021/acs.chemrev.0c00076|title=Nickel Catalyzed Olefin Oligomerization and Dimerization|year=2020|last1=Olivier-Bourbigou|first1=H.|last2=Breuil|first2=P. A. R.|last3=Magna|first3=L.|last4=Michel|first4=T.|last5=Espada Pastor|first5=M. Fernandez|last6=Delcroix|first6=D.|journal=Chemical Reviews|volume=120|issue=15|pages=7919–7983|pmid=32786672}}</ref>  In these compounds nickel is formally zerovalent Ni<sup>0</sup> and the bonding is described with the [[Chemistry:Dewar–Chatt–Duncanson model|Dewar–Chatt–Duncanson model]].  One common representative is [[Chemistry:Bis(cyclooctadiene)nickel(0)|Bis(cyclooctadiene)nickel(0)]] (Ni(COD)<sub>2</sub>), which contains two [[Chemistry:Cyclooctadiene|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&nbsp;°C, is used as a [[Chemistry:Catalyst|catalyst]] and as a precursor for many other nickel compounds.

===Allyl complexes===
[[File:Ni2(allyl)2Br2.png|150px|right|Allylnickel(II) bromide dimer.]]
[[Chemistry:Allyl|Allyl]] halides react with Ni(CO)<sub>4</sub> to form pi-allyl complexes, (allyl)<sub>2</sub>Ni<sub>2</sub>Cl<sub>2</sub>.<ref>{{OrgSynth|author=Martin F. Semmelhack and Paul M. Helquist|year=1988|title=Reaction of Aryl Halides with π-Allylnickel Halides: Methallylbenzene|volume=52|pages=115|collvol=6|collvolpages=161|prep=CV6P0722}}</ref> These compounds in turn are sources of allyl [[Chemistry:Nucleophile|nucleophile]]s. In (allyl)<sub>2</sub>Ni<sub>2</sub>Br<sub>2</sub> and (allyl)Ni(C<sub>5</sub>H<sub>5</sub>), nickel is assigned to oxidation number +2, and the electron counts are 16 and 18, respectively.

===Cyclopentadienyl complexes===
:[[File:NickeloceneStructure.png|100px|right|Nickelocene]]
[[Chemistry:Nickelocene|Nickelocene]] NiCp<sub>2</sub> with +2 Ni oxidation state and 20 valence electrons is the main [[Chemistry:Metallocene|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 Cp<sub>2</sub>Ni<sub>2</sub>(CO)<sub>3</sub>.

===Carbene complexes===
Nickel forms [[Chemistry:Transition metal carbene complex|carbene]] complexes, formally featuring C=Ni double bonds.<ref>{{cite journal |doi=10.1021/acs.chemrev.8b00505|title=N-Heterocyclic Carbene Complexes of Copper, Nickel, and Cobalt|year=2019|last1=Danopoulos|first1=Andreas A.|last2=Simler|first2=Thomas|last3=Braunstein|first3=Pierre|journal=Chemical Reviews|volume=119|issue=6|pages=3730–3961|pmid=30843688}}</ref>
:[[File:NiCarbenes.png|400px|Nickel carbenes]]

==Reactions==

===Alkene/alkyne oligomerizations===
Nickel compounds catalyze the oligomerization of [[Chemistry:Alkene|alkene]]s and [[Chemistry:Alkyne|alkyne]]s. This property validated the research and development of [[Chemistry:Ziegler–Natta catalyst|Ziegler–Natta catalyst]]s in the 1950s. That discovery shown by nickel impurities originating from an [[Organization:Autoclave|autoclave]] which killed the propagation reaction (''Aufbau'') in favor of termination reaction to a terminal [[Chemistry:Alkene|alkene]]: the polymerization of [[Chemistry:Ethylene|ethylene]] suddenly stopped at 1-butene. 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 [[Chemistry:Reppe synthesis|Reppe synthesis]]; for example in the synthesis of [[Chemistry:Cyclooctatetraene|cyclooctatetraene]]:

:[[File:Reppe Synthesis COT.svg|frameless|upright=1.5|Reppe's synthesis of cyclooctatetraene]]

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

Formal [2+2+2]cycloadditions also take place in [[Chemistry:Alkyne trimerisation|alkyne trimerisation]]. This extensible trimerisation can generally include [[Chemistry:Benzyne|benzyne]].<ref>{{cite journal | title = Nickel-catalyzed cocyclotrimerization of arynes with diynes; a novel method for synthesis of naphthalene derivatives | author = Jen-Chieh Hsieh and Chien-Hong Cheng | journal = Chemical Communications | year = 2005 | volume = 2005 | issue = 19 | pages = 2459–2461 | doi = 10.1039/b415691a| pmid = 15886770 }}</ref> Benzyne is generated [[Biology:In situ|in situ]] from a [[Chemistry:Benzene|benzene]] compound attached to a [[Chemistry:Triflate|triflate]] and a [[Chemistry:Trimethylsilyl|trimethylsilyl]] [[Chemistry:Substituent|substituent]] in the ortho- positions and reacts with a di-yne such as 1,7-octadiyne along with a [[Chemistry:Nickel(II) bromide|nickel(II) bromide]] / [[Chemistry:Zinc|zinc]] catalyst system (NiBr<sub>2</sub> [[Chemistry:1,2-Bis(diphenylphosphino)ethane|bis(diphenylphosphino) ethane]] / Zn) to synthesize the corresponding [[Chemistry:Naphthalene|naphthalene]] derivative.

[[File:AlkyneTrimerizationInvolvingAnAryne.png|400px|Alkyne trimerization involving an aryne]]

In the [[Chemistry:Catalytic cycle|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 [[Chemistry:Benzyne|benzyne]] which gives a C-H insertion reaction to the nickelcycloheptatriene compound. [[Chemistry:Reductive elimination|Reductive elimination]] 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:<ref>''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}}</ref><ref>Reaction of the [[Chemistry:Imine|imine]] N-(benzenesulfonyl)benzaldimine with two equivalents of [[Chemistry:Diphenylacetylene|diphenylacetylene]] with NiCOD<sub>2</sub> and [[Chemistry:Tricyclohexylphosphine|tricyclohexylphosphine]] first to nickelapyrroline and with a second insertion a nickeldihydroazepine and finally on heating a [[Chemistry:Dihydropyridine|dihydropyridine]]</ref>

:[[File:Nickeldihydroazepine.png|400px|Reaction of N-(benzenesulfonyl)benzaldimine with two equivalents of diphenylacetylene]]

It is noted in one study <ref>''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}}</ref> that this reaction only works with acetylene itself or with simple alkynes due to poor [[Chemistry:Regioselectivity|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:
:[[File:ReppeApplication.svg|550px|Reppe application Wender 2007]]
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 [[Chemistry:Coupling reaction|coupling reaction]] between [[Chemistry:Allyl|allyl]] and [[Chemistry:Aryl|aryl]] [[Chemistry:Halide|halide]]s. Other coupling reactions involving nickel in [[Chemistry:Catalytic cycle|catalytic amounts]] are the [[Chemistry:Kumada coupling|Kumada coupling]] and the [[Chemistry:Negishi coupling|Negishi coupling]].

:[[File:Organonickelcouplings.png|400px|Coupling of 3-Chloro-2-methyl-1-propene to 2,5-dimethyl-1,6-hexadiene]]

===Ni carbonylation===
Ni catalyzes the addition of [[Chemistry:Carbon monoxide|carbon monoxide]] to alkenes and alkynes. The industrial production of [[Chemistry:Acrylic acid|acrylic acid]] at one time consisted of combining [[Chemistry:Acetylene|acetylene]], [[Chemistry:Carbon monoxide|carbon monoxide]] and water at 40-55 atm and 160-200&nbsp;°C with [[Chemistry:Nickel(II) bromide|nickel(II) bromide]] and a copper halide.

:[[File:NickelCatalyzedCarbonylation.png|400px|Nickel catalyzed carbonylation of acetylene to acrylic acid]]

==See also==
* [[Chemistry:Nickel(II) precatalysts|Nickel(II) precatalysts]]

==Further reading==
*{{cite book |doi=10.1016/B978-0-12-388401-5.X5001-5|title=The Organic Chemistry of Nickel Volume I: Organonickel Complexes|year=1974|isbn=9780123884015|editor=P.W. Jolly, G. Wilke|publisher=Academic Press}}

==References==
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[[Category:Organonickel compounds| ]]

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