cyclooctadiene iridium chloride dimer
{{Chembox
|ImageFile1 = Ir2Cl2 cod 2improved.svg
|ImageFile2 = Cyclooctadiene-iridium-chloride-dimer-from-xtal-3D-bs-17.png
|ImageFile3 = Ir2Cl2(cod)2.jpg
|ImageSize3 = 166 px
| OtherNames = Bis(1,5-cyclooctadiene)diiridium(I) dichloride
|Section1={{Chembox Identifiers
|CASNo = 12112-67-3
|PubChem = 5365616
|PubChem_Comment = PubChem has wrong formula
|EC_number = 235-170-7
|ChemSpiderID = 21171240
|SMILES = C1/C=C\CC/C=C\C1.C1/C=C\CC/C=C\C1.[Cl].[Cl].[Ir].[Ir]
}}
|Section2={{Chembox Properties
|Formula = C16H24Cl2Ir2
|MolarMass = 671.70
|Appearance = red-orange solid
|Density = 2.65 g/cm3 (red polymorph)
}}
|Section3={{Chembox Hazards
|GHSPictograms = {{GHS07}}
|GHSSignalWord = Warning
|HPhrases = {{H-phrases|302|312|315|319|335}}
|PPhrases = {{P-phrases|261|264|270|271|280|301+312|302+352|304+340|305+351+338|312|321|322|330|332+313|337+313|362|363|403+233|405|501}}
}}
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Cyclooctadiene iridium chloride dimer is an organoiridium compound with the formula [Ir(μ2-Cl)(COD)]2, where COD is the diene 1,5-cyclooctadiene (C8H12). It is an orange-red solid that is soluble in organic solvents. The complex is used as a precursor to other iridium complexes, some of which are used in homogeneous catalysis.J. Hartwig, "Organotransition Metal Chemistry: From Bonding to Catalysis" University Science Books, 2009. {{ISBN|978-1891389535}}. The solid is air-stable but its solutions degrade in air.
Preparation, structure, reactions
The compound is prepared by heating hydrated iridium trichloride and cyclooctadiene in alcohol solvent. In the process, Ir(III) is reduced to Ir(I).{{cite book|first1=J. L.|last1=Herdé|first2=J. C.|last2=Lambert|first3=C. V.|last3=Senoff|title=Inorganic Syntheses|chapter=Cyclooctene and 1,5-Cyclooctadiene Complexes of Iridium(I)|year=1974|volume=15|pages=18–20|doi=10.1002/9780470132463.ch5|isbn=9780470132463}}
In terms of its molecular structure, the iridium centers are square planar as is typical for a d8 complex. The Ir2Cl2 core is folded with a dihedral angle of 86°. The molecule crystallizes in yellow-orange and red-orange polymorphs; the latter one is more common.F. Albert Cotton, Pascual Lahuerta, Mercedes Sanau, Willi Schwotzer "Air oxidation of Ir2(Cl)2(COD)2 revisited. The structures of [Ir(μ2-Cl)(COD)]2 (ruby form) and its oxidation product, Ir2Cl2(COD)2(μ2-OH)2(μ2-O)" Inorganica Chimica Acta, 1986 vol. 120, Pages 153–157. {{doi|10.1016/S0020-1693(00)86102-2}}Tabrizi, D., Manoli, J. M., Dereigne, A., "Etude radiocristallographique de μ-dichloro-bis (π cyclooctadiène-1,5) diiridium: [(COD-1,5)IrCl]2, variété jaune-orange", Journal of the Less Common Metals 1970, vol. 21, pp. 337. {{doi|10.1016/0022-5088(70)90155-4}}
The complex is widely used precursor to other iridium complexes. A notable derivative is Crabtree's catalyst.{{cite book|first1=Robert H.|last1=Crabtree|first2=Sheila M.|last2=Morehouse|title=[η4-1,5-Cyclooctadiene)(Pyridine)(Tricyclohexylphosphine)Iridium(I)Hexafluorophosphate|chapter=[η4 -1,5-Cyclooctadiene)(Pyridine)-(Tricyclohexylphosphine)Iridium(I)Hexafluorophosphate|series= Inorganic Syntheses|year=1986|volume=24|pages=173–176|doi=10.1002/9780470132555.ch50|isbn=9780470132555}} The chloride ligands can also be replaced with methoxide to give cyclooctadiene iridium methoxide dimer, Ir2(OCH3)2(C8H12)2.{{cite book|doi=10.1002/9780470132548.ch25|isbn=9780470132548|title=Inorganic Syntheses|year=1985|last1=Uson|first1=R.|last2=Oro|first2=L. A.|last3=Cabeza|first3=J. A.|chapter=Dinuclear Methoxy, Cyclooctadiene, and Barrelene Complexes of Rhodium(I) and Iridium(I) |volume=23|pages=126–130}} The cyclooctadiene ligand is prone to isomerize in cationic complexes of the type [(C8H12)IrL2]+.{{cite journal|doi=10.1021/om034218g|title=Versatility of Cyclooctadiene Ligands in Iridium Chemistry and Catalysis|year=2003|last1=Martín|first1=Marta|last2=Sola|first2=Eduardo|last3=Torres|first3=Olga|last4=Plou|first4=Pablo|last5=Oro|first5=Luis A.|journal=Organometallics|volume=22|issue=26|pages=5406–5417}}