Browse history interactively

Page 1

Page 1Revision 1

Page 2

Page 2Revision 2

← Previous editContent deleted Content addedVisualWikitext

Revision as of 09:40, 9 July 2011 editAmirobot (talk | contribs)56,602 editsm r2.7.1) (robot Adding: zh:八羰基二钴← Previous edit		Latest revision as of 17:18, 4 July 2024 edit undoDMacks (talk | contribs)Edit filter managers, Autopatrolled, Administrators186,427 edits MOS for image placement: in section where relevant, not dangling down from preceding
(152 intermediate revisions by 56 users not shown)
Line 1:		Line 1:
			{{short description|Chemical compound}}
	{{chembox		{{chembox
	| Watchedfields = changed		|Verifiedfields = changed
			|Watchedfields = changed
	| verifiedrevid = 396340589
			|verifiedrevid = 438551689
	| Name = Dicobalt octacarbonyl
	| ImageFile = Dicobcalt-octacarbonyl-from-xtal-3D-balls.png		|Name = Dicobalt octacarbonyl
	| ImageName = Dicobalt octacarbonyl		|ImageFile = Dicobalt-octacarbonyl-C2v-bridged-from-xtal-1983-3D-balls-A.png
	| ImageFile1 = Dicobalt-octacarbonyl-non-bridged-3D-balls.png		|ImageName = Dicobalt octacarbonyl, bridged C2v isomer
	| ImageName1 = Dicobalt octacarbonyl		|ImageFile1 = Dicobalt octacarbonyl.png
			|ImageCaption1 = Co<sub>2</sub>(CO)<sub>8</sub> soaked in ]
	| IUPACName = Octacarbonyldicobalt(''Co—Co'')
			|IUPACName = Octacarbonyldicobalt(''Co—Co'')
	| OtherNames = Cobalt carbonyl
			|OtherNames = Cobalt carbonyl (2:8), di-mu-Carbonylhexacarbonyldicobalt, Cobalt octacarbonyl, Cobalt tetracarbonyl dimer, Dicobalt carbonyl, Octacarbonyldicobalt
	| Section1 = {{Chembox Identifiers
			|Section1 = {{Chembox Identifiers
	| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
			|ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
	| ChemSpiderID = 2007057
			|ChemSpiderID = 2007057
	| InChI = 1/8CO.2Co/c8*1-2;;/q;;;;;;;;2*+2
			|PubChem = 25049
	| SMILES = ..#.#.#.#.#.#.#.#
			|InChI = 1/8CO.2Co/c8*1-2;;/q;;;;;;;;2*+2
	| InChIKey = MQIKJSYMMJWAMP-UHFFFAOYAG
			|SMILES = O=C=1(=C=O)(=C=O)C(=O)(=C=O)(=C=O)(=C=O)C1=O
	| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
			|SMILES1 = O=C=(=C=O)(=C=O)(=C=O)(=C=O)(=C=O)(=C=O)=C=O
	| StdInChI = 1S/8CO.2Co/c8*1-2;;/q;;;;;;;;2*+2
			|InChIKey = MQIKJSYMMJWAMP-UHFFFAOYAG
	| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
			|StdInChI_Ref = {{stdinchicite|correct|chemspider}}
	| StdInChIKey = MQIKJSYMMJWAMP-UHFFFAOYSA-N
			|StdInChI = 1S/8CO.2Co/c8*1-2;;/q;;;;;;;;2*+2
	| CASNo = 10210-68-1
	| CASNo_Ref = {{cascite|correct|CAS}}		|StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
			|StdInChIKey = MQIKJSYMMJWAMP-UHFFFAOYSA-N
	| UNNumber = 3281
			|CASNo = 10210-68-1
	| RTECS = GG0300000
			|CASNo_Ref = {{cascite|correct|CAS}}
	}}
			|EINECS = 233-514-0
	| Section2 = {{Chembox Properties
			|UNII_Ref = {{fdacite|correct|FDA}}
	| Formula = Co<sub>2</sub>(CO)<sub>8</sub>
			|UNII = MDH533S43Q
	| MolarMass = 341.95 g/mol
			|UNNumber = 3281
	| Appearance = red-orange crystals<br />when pure
			|RTECS = GG0300000
	| Density = 1.87 g/cm<sup>3</sup>
			}}
	| Solubility = insoluble
			|Section2 = {{Chembox Properties
	| MeltingPtCL = 51
			|Formula = {{chem2|Co2(CO)8}}
	| MeltingPtCH = 52
			|MolarMass = 341.95 g/mol
	| BoilingPtC = 52
			|Appearance = red-orange crystals<br />
	| Boiling_notes = decomp. ca.
			|Density = 1.87 g/cm<sup>3</sup>
	}}
			|Solubility = insoluble
	| Section3 = {{Chembox Structure
			|MeltingPtC = 51 to 52
	| Dipole = 1.33 ] (C<sub>2v</sub> isomer)<br />0 ] (D<sub>3d</sub> isomer)
			|BoilingPtC = 52
	}}
			|BoilingPt_notes = decomposes
	| Section7 = {{Chembox Hazards
			|VaporPressure = 0.7 mmHg (20&nbsp;°C)<ref name=PGCH/>
	| ExternalMSDS =
			}}
	| MainHazards = Toxic
			|Section3 = {{Chembox Structure
	| FlashPt =
			|Dipole = 1.33 ] (C<sub>2v</sub> isomer)<br />0 ] (D<sub>3d</sub> isomer)
	| RPhrases =
			}}
	| SPhrases =
			|Section4 = {{Chembox Hazards
	}}
			|MainHazards = Potential carcinogen
	| Section8 = {{Chembox Related
			|NFPA-H = 4
	| Function = metal carbonyls
			|NFPA-F = 3
	| OtherFunctn = ]<br />]<br />]
			|NFPA-R = 1
	}}
			|ExternalSDS =
			|FlashPt = -23 °C (-9.4 °F)
			|FlashPt_ref = <ref name=PGCH/>
			|GHSPictograms = {{GHS02}}{{GHS06}}{{GHS07}}{{GHS08}}
			|GHSSignalWord = Danger
			|HPhrases = {{H-phrases|251|302|304|315|317|330|351|361|412}}
			|PPhrases = {{P-phrases|201|260|273|280|304+340+310|403+233}}
			|PEL = none<ref name=PGCH>{{PGCH|0147}}</ref>
			|IDLH = N.D.<ref name=PGCH/>
			|REL = TWA 0.1 mg/m<sup>3</sup><ref name=PGCH/>
			|LD50 = 15 mg/kg (oral, rat)
			}}
			|Section5 = {{Chembox Related
			|OtherFunction_label = metal carbonyls
			|OtherFunction = ]<br />]<br />]
			}}
	}}		}}
	'''Dicobalt octacarbonyl''' is the ] Co<sub>2</sub>(CO)<sub>8</sub>. This ] is a ] and ] in ] and ].<ref>Pauson, P. L. “Octacarbonyldicobalt” in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. {{DOI|10.1002/047084289}}{{Dead link|date=July 2010}}.</ref> It is used as a catalyst for ], the conversion of ]s to ]s.<ref>Elschenbroich, C.; Salzer, A. ”Organometallics : A Concise Introduction” (2nd Ed) (1992) Wiley-VCH: Weinheim. ISBN 3-527-28165-7</ref>		'''Dicobalt octacarbonyl''' is an ] with composition {{chem2|Co2(CO)8}}. This ] is used as a ] and ] in ] and ], and is central to much known ].<ref name = Pauson>{{cite encyclopedia|first1 = Peter L.|last1 = Pauson|authorlink1 = Peter Pauson|first2 = James P.|last2 = Stambuli|first3 = Teh-Chang|last3 = Chou|first4 = Bor-Cherng|last4 = Hong|title = Octacarbonyldicobalt|encyclopedia = ]|year = 2014|pages = 1–26|doi = 10.1002/047084289X.ro001.pub3|publisher = ]|isbn = 9780470842898}}</ref><ref name = Ullmann /> It is the parent member of a family of ] catalysts.<ref name = ElschSalzer>{{cite book|last1 = Elschenbroich|first1 = C.|last2 = Salzer|first2 = A.|title = Organometallics: A Concise Introduction|edition = 2nd|year = 1992|publisher = ]|location = Weinheim|isbn = 3-527-28165-7}}</ref> Each ] consists of two ] atoms bound to eight ] ]s, although multiple structural isomers are known.<ref name = SolutionStructures /> Some of the carbonyl ligands are ].
	==Synthesis, structure, properties==		==Synthesis, structure, properties==
			Dicobalt octacarbonyl an orange-colored, ] solid.<ref name=IS/> It is synthesised by the high pressure ] of cobalt(II) ]:<ref name=IS>{{cite book |doi=10.1002/9780470132333.ch76|title=Dicobalt Octacarbonyl, Cobalt Nitrosyl Tricarbonyl, and Cobalt Tetracarbonyl Hydride |series=Inorganic Syntheses |year=1946 |last1=Gilmont |first1=Paul |last2=Blanchard |first2=Arthur A. |pages=238–243 |isbn=9780470132333|volume =2 }}</ref>
	The high pressure ] of cobalt(II) salts, often in the presence of ], affords this compound. It is an orange-colored, ] solid that is thermally unstable. It exists as two isomers in solution:<ref>Ray L. Sweany and Theodore L. Brown "Infrared spectra of matrix-isolated dicobalt octacarbonyl. Evidence for the third isomer" Inorganic Chemistry 1977, 16, pp 415 - 421. {{DOI|10.1021/ic50168a037}}</ref>
	:]
			:{{chem2|2 (CH3COO)2Co + 8 CO + 2 H2 → Co2(CO)8 + 4 CH3COOH}}
	The predominant isomer resembles Fe<sub>2</sub>(CO)<sub>9</sub>, less one bridging CO. The Co-Co distance is 2.52 Å, and the Co-CO<sub>terminal</sub> and Co-CO<sub>bridge</sub> distances are 1.80 and 1.90 Å, respectively.<ref>G.G. Sumner, HP Klug, LE Alexander "The crystal structure of dicobalt octacarbonyl" Acta Crystallographica, 1964 Volume 17 Part 6 Pages 732-742. {{DOI|10.1107/S0365110X64001803}}</ref> These ]s rapidly interconvert. The minor isomer has no bridging CO ligands; it is described (CO)<sub>4</sub>Co-Co(CO)<sub>4</sub> (D<sub>3d</sub> ]). The major isomer contains two bridging CO ligand and features ] cobalt, describable as (CO)<sub>3</sub>Co(μ-CO)<sub>2</sub>Co(CO)<sub>3</sub> (C<sub>2v</sub> ]). The minor isomer has been crystallized together with C<sub>60</sub>.<ref>"Splendid symmetry: crystallization of an unbridged isomer of Co<sub>2</sub>(CO)<sub>8</sub> in Co<sub>2</sub>(CO)<sub>8</sub><sup>·</sup>C<sub>60</sub>" Thelma Y. Garcia, James C. Fettinger, Marilyn M. Olmstead, Alan L. Balch, Chem. Commun., 2009. {{DOI|10.1039/b915083h}}.</ref>
			The preparation is often carried out in the presence of ], converting the cobalt(II) salt into a ](II) complex that reacts with carbon monoxide to yield {{chem2|K}}. Acidification produces ], {{chem2|HCo(CO)4}}, which degrades near room temperature to dicobalt octacarbonyl and hydrogen.<ref name = Ullmann /><ref name = cyanide>{{cite book|chapter = Hydrogenation of Organic Compounds with Synthesis Gas|first = Milton|last = Orchin|title = Advances in Catalysis|year = 1953|volume = 5|pages = 385–415|chapter-url = https://books.google.com/books?id=f_Oiij4V98cC&pg=PA409|publisher = ]|isbn = 9780080565095}}</ref> It can also be prepared by heating cobalt metal to above 250&nbsp;°C in a stream of ] gas at about 200 to 300&nbsp;]:<ref name = Ullmann />
			:{{chem2|2 Co + 8 CO → Co2(CO)8}}
			It exist as a mixture of rapidly interconverting ]s.<ref name = Pauson /><ref name = Ullmann /> In solution, there are two isomers known that rapidly interconvert:<ref name = SolutionStructures>{{cite journal|first1 = Ray L.|last1 = Sweany|first2 = Theodore L.|last2 = Brown|authorlink2 = Theodore L. Brown|title = Infrared spectra of matrix-isolated dicobalt octacarbonyl. Evidence for the third isomer|journal = ]|year = 1977|volume = 16|issue = 2|pages = 415–421|doi = 10.1021/ic50168a037}}</ref>
			:]
			The major isomer (on the left in the above ] process) contains two bridging carbonyl ligands linking the cobalt centres and six terminal carbonyl ligands, three on each metal.<ref name = SolutionStructures /> It can be summarised by the formula {{chem2|(CO)3Co(μ\-CO)2Co(CO)3}} and has C<sub>2v</sub> ]. This structure resembles ] ({{chem2|Fe2(CO)9}}) but with one fewer bridging carbonyl. The Co–Co distance is 2.52&nbsp;Å, and the Co–CO<sub>terminal</sub> and Co–CO<sub>bridge</sub> distances are 1.80 and 1.90&nbsp;Å, respectively.<ref>{{cite journal|first1 = G. Gardner|last1 = Sumner|first2 = Harold P.|last2 = Klug|first3 = Leroy E.|last3 = Alexander|title = The crystal structure of dicobalt octacarbonyl|journal = ]|year = 1964|volume = 17|issue = 6|pages = 732–742|doi = 10.1107/S0365110X64001803|doi-access = free}}</ref> Analysis of the bonding suggests the absence of a direct cobalt&ndash;cobalt bond.<ref>{{cite journal|first1 = Jennifer C.|last1 = Green|first2 = Malcolm L. H.|last2 = Green|authorlink2 = Malcolm Green (chemist)|first3 = Gerard|last3 = Parkin|authorlink3 = Gerard Parkin|title = The occurrence and representation of three-centre two-electron bonds in covalent inorganic compounds|journal = ]|year = 2012|volume = 2012|issue = 94|pages = 11481–11503|doi = 10.1039/c2cc35304k|pmid = 23047247}}</ref>
			The minor isomer has no bridging carbonyl ligands, but instead has a direct bond between the cobalt centres and eight terminal carbonyl ligands, four on each metal atom.<ref name = SolutionStructures /> It can be summarised by the formula {{chem2|(CO)4Co\–Co(CO)4}} and has D<sub>4d</sub> symmetry. It features an unbridged cobalt&ndash;cobalt bond that is 2.70&nbsp;Å in length in the solid structure when crystallized together with ].<ref>{{cite journal|first1 = Thelma Y.|last1 = Garcia|first2 = James C.|last2 = Fettinger|first3 = Marilyn M.|last3 = Olmstead|first4 = Alan L.|last4 = Balch|title = Splendid symmetry: Crystallization of an unbridged isomer of Co<sub>2</sub>(CO)<sub>8</sub> in Co<sub>2</sub>(CO)<sub>8</sub><sup>·</sup>C<sub>60</sub>|journal = ]|year = 2009|volume = 2009|issue = 46|pages = 7143–7145|doi = 10.1039/b915083h|pmid = 19921010}}</ref>
			{{Gallery
			| title = Isomers of dicobalt octacarbonyl
			| File:Dicobalt-octacarbonyl-C2v-bridged-from-xtal-1983-3D-balls-A.png
			| Bridged C<sub>2v</sub> isomer
			| File:Dicobalt-octacarbonyl-D3d-non-bridged-from-C60-xtal-2009-3D-balls.png
			| non-bridged D<sub>3d</sub> isomer
			| File:Dicobalt-octacarbonyl-D2d-non-bridged-3D-balls.png
			| nonbridged D<sub>2d</sub> isomer
			}}
	==Reactions==		==Reactions==
			===Reduction===
	The most characteristic reaction of Co<sub>2</sub>(CO)<sub>8</sub> is its hydrogenation to ], :
			Dicobalt octacarbonyl is reductively cleaved by alkali metals and related reagents, such as ]. The resulting salts protonate to give ]:<ref name = Ullmann>{{cite encyclopedia|last1 = Donaldson|first1 = John Dallas|last2 = Beyersmann|first2 = Detmar|year = 2005|title = Cobalt and Cobalt Compounds|encyclopedia = ]|publisher = Wiley-VCH|doi = 10.1002/14356007.a07_281.pub2|isbn = 3527306730}}</ref>
	:Co<sub>2</sub>(CO)<sub>8</sub> + H<sub>2</sub> → 2 HCo(CO)<sub>4</sub>
			:{{chem2|Co2(CO)8 + 2 Na → 2 Na}}
	This hydride is the active agent in hydroformylation. It adds to ]s to give an alkyl-Co(CO)<sub>4</sub> product that then proceeds to insert CO and undergo hydrogenolysis to afford the ]. Reduction of Co<sub>2</sub>(CO)<sub>8</sub> gives the ] of HCo(CO)<sub>4</sub>:
	:Co<sub>2</sub>(CO)<sub>8</sub> + 2 Na → 2 NaCo(CO)<sub>4</sub>		:{{chem2|Na + H+ → H + Na+}}
			Salts of this form are also intermediates in the cyanide synthesis pathway for dicobalt octacarbonyl.<ref name = cyanide />
	The CO ligands can be replaced with tertiary ] ]s to give Co<sub>2</sub>(CO)<sub>8-x</sub>(PR<sub>3</sub>)<sub>x</sub>. These bulky derivatives are more selective catalysts for hydroformylation reactions. "]" Lewis bases, e.g. ], cause ]:
	:6 C<sub>6</sub>H<sub>5</sub>N + 1.5 Co<sub>2</sub>(CO)<sub>8</sub> → <sub>2</sub> + 4 CO
			===Reactions with electrophiles===
	Co<sub>2</sub>(CO)<sub>8</sub> catalyzes the ] of an ], an ], and CO to give cyclopentenones.
			Halogens and related reagents cleave the Co–Co bond to give pentacoordinated halotetracarbonyls:
			:{{chem2|Co2(CO)8 + Br2 → 2 Br}}
			] is produced by treatment of dicobalt octacarbonyl with nitric oxide:
	Heating causes decarbonylation and formation of the tetrahedral cluster:
	:2 Co<sub>2</sub>(CO)<sub>8</sub> → Co<sub>4</sub>(CO)<sub>12</sub> + 4 CO		:{{chem2|Co2(CO)8 + 2 NO → 2 Co(CO)3NO + 2 CO}}
			===Reactions with alkynes===
	==Safety==
			The ] is a ] whereby an alkoxy group located on the α-carbon of an ] is replaced by another ]. The alkyne reacts first with dicobalt octacarbonyl, from which is generated a stabilized ]ic ] that reacts with the incoming nucleophile and the product then forms by ].<ref name = NicholasRev1>{{cite journal|last = Nicholas|first = Kenneth M.|title = Chemistry and synthetic utility of cobalt-complexed propargyl cations|journal = ]|year = 1987|volume = 20|issue = 6|pages = 207–214|type = Review|doi = 10.1021/ar00138a001}}</ref><ref name = NicholasRev2>{{cite journal|last = Teobald|first = Barry J.|journal = ]|year = 2002|title = The Nicholas reaction: The use of dicobalt hexacarbonyl-stabilised propargylic cations in synthesis|volume = 58|issue = 21|pages = 4133–4170|type = Review|doi = 10.1016/S0040-4020(02)00315-0}}</ref>
	Co<sub>2</sub>(CO)<sub>8</sub> a volatile source of cobalt(0), is ] and releases ] upon decomposition.<ref></ref>
			]
	==See also==
	*]
			The ],<ref name = PK>{{cite journal|first1 = P. L.|last1 = Pauson|authorlink1 = Peter Pauson|first2 = I. U.|last2 = Khand|journal = ]|year = 1977|title = Uses of Cobalt-Carbonyl Acetylene Complexes in Organic Synthesis|volume = 295|issue = 1|pages = 2–14|doi = 10.1111/j.1749-6632.1977.tb41819.x|bibcode = 1977NYASA.295....2P|s2cid = 84203764}}</ref> in which an ], an alkene, and carbon monoxide cyclize to give a ], can be catalyzed by {{chem2|Co2(CO)8}},<ref name = Ullmann /><ref name = PK-review>{{cite journal|title = The Pauson&ndash;Khand reaction, a powerful synthetic tool for the synthesis of complex molecules|year = 2004|first1 = Jaime|last1 = Blanco-Urgoiti|first2 = Loreto|last2 = Añorbe|first3 = Leticia|last3 = Pérez-Serrano|first4 = Gema|last4 = Domínguez|first5 = Javier|last5 = Pérez-Castells|journal = ]|volume = 33|issue = 1|pages = 32–42|doi = 10.1039/b300976a|pmid = 14737507}}</ref> though newer methods that are more efficient have since been developed:<ref>{{cite journal|last = Schore|first = Neil E.|authorlink = Neil E. Schore|title = The Pauson&ndash;Khand Cycloaddition Reaction for Synthesis of Cyclopentenones|journal = ]|year = 1991|volume = 40|pages = 1–90|doi = 10.1002/0471264180.or040.01|isbn = 0471264180}}</ref><ref>{{cite journal|first1 = Susan E.|last1 = Gibson|first2 = Andrea|last2 = Stevenazzi|title = The Pauson&ndash;Khand Reaction: The Catalytic Age Is Here!|journal = ]|year = 2003|volume = 42|issue = 16|pages = 1800–1810|doi = 10.1002/anie.200200547|pmid = 12722067}}</ref>
			]
			<!-- diagram would be useful here -->
			{{chem2|Co2(CO)8}} reacts with ]s to form a stable covalent complex, which is useful as a ] for the alkyne. <!-- Deprotection to regenerate the alkyne is accomplished using...? --> This complex itself can also be used in the Pauson–Khand reaction.<ref name = PK />
			Intramolecular Pauson–Khand reactions, where the starting material contains both the alkene and alkyne moieties, are possible. In the ] of the '']'' ] ], Takayama and co-workers used an intramolecular Pauson–Khand reaction to cyclise an ] containing a ''tert''-butyldiphenylsilyl (TBDPS) ] primary alcohol.<ref>{{cite journal|title = Asymmetric Total Synthesis of a Pentacyclic ''Lycopodium'' Alkaloid: Huperzine-Q|first1 = Atsushi|last1 = Nakayama|first2 = Noriyuki|last2 = Kogure|first3 = Mariko|last3 = Kitajima|first4 = Hiromitsu|last4 = Takayama|year = 2011|journal = ]|doi = 10.1002/anie.201103550|volume = 50|issue = 35|pages = 8025–8028|pmid = 21751323}}</ref> The preparation of the cyclic siloxane moiety immediately prior to the introduction of the dicobalt octacarbonyl ensures that the product is formed with the desired ].<ref name = Fiesers>{{cite book|chapter = Dicobalt Octacarbonyl|year = 2016|chapter-url = https://books.google.com/books?id=AO3bCwAAQBAJ&pg=PA251|pages = 251–252|title = Fiesers' Reagents for Organic Synthesis|volume = 28|first = Tse-Lok|last = Ho|publisher = ]|isbn = 9781118942819}}</ref>
			]
			Dicobalt octacarbonyl can catalyze ] of ] and its derivatives to ]s.<ref>{{cite journal |last1=Vij |first1=V. |last2=Bhalla |first2=V. |last3=Kumar |first3=M. |date=8 August 2016 |title=Hexaarylbenzene: Evolution of Properties and Applications of Multitalented Scaffold |journal=] |volume=116 |issue=16 |pages=9565–9627 |doi=10.1021/acs.chemrev.6b00144}}</ref> Symmetrical diphenylacetylenes form 6-substituted hexaphenylbenzenes, while asymmetrical diphenylacetylenes form a mixture of two isomers.<ref>{{cite journal |last1=Xiao |first1=W. |last2=Feng |first2=X. |last3=Ruffieux |first3=P. |last4=Gröning |first4=O. |last5=Müllen |first5=K. |last6=Fasel |first6=R.|date=18 June 2008 |title=Self-Assembly of Chiral Molecular Honeycomb Networks on Au(111) |journal=] |volume=130 |issue=28 |pages=8910–8912 |doi=10.1021/ja7106542}}</ref>
			]
			]
			===Hydroformylation===
			] for the ] of a ] ({{chem2|RCH\dCH2}}) to an ] ({{chem2|RCH2CH2CHO}}):<ref name = ElschSalzer />{{Ordered list
			|] dissociates from ] to form the active catalyst, {{nowrap|{{chem2|HCo(CO)3}}}}
			|The cobalt centre ] to the alkene
			|The alkene ligand inserts into the cobalt&ndash;hydride bond
			|An additional carbonyl ligand coordinates
			|A carbonyl ligand ] into the cobalt&ndash;alkyl bond<ref name = Heck>{{cite journal|first1 = Richard F.|last1 = Heck|authorlink1 = Richard F. Heck|first2 = David S.|last2 = Breslow| author-link2=David S. Breslow |title = The Reaction of Cobalt Hydrotetracarbonyl with Olefins|journal = ]|volume = 83|issue = 19|year = 1961|pages = 4023–4027|doi = 10.1021/ja01480a017}}</ref>
			|] ] to the ]
			|The ] ] the aldehyde product,<ref name = Halpern>{{cite journal|first = Jack|last = Halpern|authorlink = Jack Halpern (chemist)|title = Organometallic chemistry at the threshold of a new millennium. Retrospect and prospect.|journal = ]|year = 2001|volume = 73|issue = 2|pages = 209–220|doi = 10.1351/pac200173020209|doi-access = free}}</ref> regenerating the catalyst
			| An unproductive and reversible ]
			}}
			]]
			] of {{chem2|Co2(CO)8}} produces ] {{chem2|H}}:<ref name = HCo(CO)4>{{cite book|first1 = M.|last1 = Pfeffer|first2 = M.|last2 = Grellier|chapter = Cobalt Organometallics|title = Comprehensive Organometallic Chemistry III |year = 2007|volume = 7|pages = 1–119|publisher = ]|doi = 10.1016/B0-08-045047-4/00096-0|isbn = 9780080450476}}</ref>
			:{{chem2|Co2(CO)8 + H2 → 2 H}}
			This hydride is a ] for ] &ndash; the conversion of ]s to ]s.<ref name = ElschSalzer /><ref name = HCo(CO)4 /> The ] for this hydroformylation is shown in the diagram.<ref name = ElschSalzer /><ref name = Heck /><ref name = Halpern />
			===Substitution reactions===
			The CO ligands can be replaced with tertiary ] ligands to give {{chem2|Co2(CO)8−_{''x''}(PR3)_{''x''}|}}. These bulky derivatives are more selective catalysts for hydroformylation reactions.<ref name = Ullmann /> "]" Lewis bases, e.g. ], cause ]:
			:{{chem2|12 C5H5N + 3 Co2(CO)8 → 2 2 + 8 CO}}
			===Conversion to higher carbonyls===
			], {{nowrap|{{chem2|HCCo3(CO)9}}}}, an ] ] compound structurally related to ] ]]
			Heating causes decarbonylation and formation of ]:<ref name = Ullmann /><ref>{{cite journal|last = Chini|first = P.|title = The closed metal carbonyl clusters|journal = ]|year = 1968|volume = 2|pages = 31–51|doi = 10.1016/0073-8085(68)80013-0}}</ref>
			:{{chem2|2 Co2(CO)8 → Co4(CO)12 + 4 CO}}
			Like many metal carbonyls, dicobalt octacarbonyl abstracts halides from alkyl halides. Upon reaction with ], it converts to ], {{chem2|HCCo3(CO)9}}, by a reaction that can be idealised as:<ref>{{cite journal<!--Stop citation bot from replacing this with cite book-->|first1 = Mara O.|last1 = Nestle|first2 = John E.|last2 = Hallgren|first3 = Dietmar|last3 = Seyferth|first4 = Peter|last4 = Dawson|first5 = Brian H.|last5 = Robinson|title=μ<sub>3</sub>-Methylidyne and μ<sub>3</sub>-Benzylidyne-Tris(Tricarbonylcobalt) |doi = 10.1002/9780470132517.ch53|journal = ]| date=2007 |volume = 20|pages = 226–229|isbn = 9780470132517}}</ref>
			:{{chem2|9 Co2(CO)8 + 4 CHBr3 → 4 HCCo3(CO)9 + 36 CO + 6 CoBr2}}
			==Safety==
			{{chem2|Co2(CO)8}} a volatile source of cobalt(0), is ] and releases ] upon decomposition.<ref></ref> The ] has ] that workers should not be exposed to concentrations greater than 0.1&nbsp;mg/m<sup>3</sup> over an eight-hour time-weighted average, without the proper respiratory gear.<ref></ref>
			{{clear}}
	==References==		==References==
	<references/>		<references/>
			{{carbonyl complexes}}
	]		]
	]		]
			]
	]
	]
	]
	]
	]