[{"@context":"http:\/\/schema.org\/","@type":"BlogPosting","@id":"https:\/\/wiki.edu.vn\/en\/pentamethylcyclopentadiene-wikipedia\/#BlogPosting","mainEntityOfPage":"https:\/\/wiki.edu.vn\/en\/pentamethylcyclopentadiene-wikipedia\/","headline":"Pentamethylcyclopentadiene – Wikipedia","name":"Pentamethylcyclopentadiene – Wikipedia","description":"before-content-x4 From Wikipedia, the free encyclopedia after-content-x4 Chemical compound 1,2,3,4,5-Pentamethylcyclopentadiene is a cyclic diene with the formula C5Me5H (Me =","datePublished":"2022-12-28","dateModified":"2022-12-28","author":{"@type":"Person","@id":"https:\/\/wiki.edu.vn\/en\/author\/lordneo\/#Person","name":"lordneo","url":"https:\/\/wiki.edu.vn\/en\/author\/lordneo\/","image":{"@type":"ImageObject","@id":"https:\/\/secure.gravatar.com\/avatar\/cd810e53c1408c38cc766bc14e7ce26a?s=96&d=mm&r=g","url":"https:\/\/secure.gravatar.com\/avatar\/cd810e53c1408c38cc766bc14e7ce26a?s=96&d=mm&r=g","height":96,"width":96}},"publisher":{"@type":"Organization","name":"Enzyklop\u00e4die","logo":{"@type":"ImageObject","@id":"https:\/\/wiki.edu.vn\/wiki4\/wp-content\/uploads\/2023\/08\/download.jpg","url":"https:\/\/wiki.edu.vn\/wiki4\/wp-content\/uploads\/2023\/08\/download.jpg","width":600,"height":60}},"image":{"@type":"ImageObject","@id":"https:\/\/upload.wikimedia.org\/wikipedia\/commons\/thumb\/5\/5e\/Cp%2AH_Synthesis_1.svg\/525px-Cp%2AH_Synthesis_1.svg.png","url":"https:\/\/upload.wikimedia.org\/wikipedia\/commons\/thumb\/5\/5e\/Cp%2AH_Synthesis_1.svg\/525px-Cp%2AH_Synthesis_1.svg.png","height":"207","width":"525"},"url":"https:\/\/wiki.edu.vn\/en\/pentamethylcyclopentadiene-wikipedia\/","wordCount":3476,"articleBody":"     (adsbygoogle = window.adsbygoogle || []).push({});before-content-x4From Wikipedia, the free encyclopedia       (adsbygoogle = window.adsbygoogle || []).push({});after-content-x4Chemical compound1,2,3,4,5-Pentamethylcyclopentadiene is a cyclic diene with the formula C5Me5H (Me = CH3).[1]  1,2,3,4,5-Pentamethylcyclopentadiene is the precursor to the ligand 1,2,3,4,5-pentamethylcyclopentadienyl, which is often denoted Cp* (C5Me5) and read as “C P star”, the “star” signifying the five methyl groups radiating from the core of the ligand. In contrast to less-substituted cyclopentadiene derivatives, Cp*H is not prone to dimerization.       (adsbygoogle = window.adsbygoogle || []).push({});after-content-x4Table of ContentsSynthesis[edit]Organometallic derivatives[edit]Comparison to other Cp ligands[edit]See also[edit]References[edit]Synthesis[edit]Pentamethylcyclopentadiene is commercially available. It was first prepared from tiglaldehyde via 2,3,4,5-tetramethylcyclopent-2-enone.[2]Alternatively, 2-butenyllithium adds to ethyl acetate followed by acid-catalyzed dehydrocyclization:[3][4]       (adsbygoogle = window.adsbygoogle || []).push({});after-content-x4  Sample of pentamethylcyclopentadiene in ampoule.Organometallic derivatives[edit]Cp*H is a precursor to organometallic compounds containing the C5Me\u22125 ligand, commonly called Cp*\u2212.[5]Cp*\u2013metal complexesCp*2FeyellowCp*TiCl3red[Cp*Fe(CO)2]2red-violet[Cp*RhCl2]2red[Cp*IrCl2]2orangeCp*Re(CO)3colorlessCp*Mo(CO)2CH3orangeSome representative reactions leading to such Cp*\u2013metal complexes follow:[6]Deprotonation with  n-butyllithium:Cp*H   +  C4H9Li \u2192   Cp*Li  +  C4H10Synthesis of (pentamethylcyclopentadienyl)titanium trichloride:Cp*Li  + TiCl4 \u2192   Cp*TiCl3  + LiClSynthesis of (pentamethylcyclopentadienyl)iron dicarbonyl dimer from iron pentacarbonyl:2\u00a0Cp*H  +  2 Fe(CO)5]]   \u2192   [\u03b75-Cp*Fe(CO)2]2  +  H2  +  6 COThis method is analogous to the route to the related Cp complex, see cyclopentadienyliron dicarbonyl dimer.Some Cp* complexes are prepared using silyl transfer:Cp*Li + Me3SiCl \u2192 Cp*SiMe3 + LiClCp*SiMe3 + TiCl4 \u2192 Cp*TiCl3 + Me3SiClAn instructive but obsolete route to Cp* complexes involves the use of hexamethyl Dewar benzene.  This method was traditionally used for preparation of the chloro-bridged dimers [Cp*IrCl2]2 and [Cp*RhCl2]2, but has been discontinued with the increased commercial availability of Cp*H.  Such syntheses rely on a hydrohalic acid induced rearrangement of hexamethyl Dewar benzene[7][8] to a substituted pentamethylcyclopentadiene prior to reaction with the hydrate of either iridium(III) chloride[9] or rhodium(III) chloride.[10]Comparison to other Cp ligands[edit]Complexes of pentamethylcyclopentadienyl differ in several ways from the more common cyclopentadienyl (Cp) derivatives.  Being more electron-rich, Cp*\u2212 is a stronger donor and dissociation, like ring-slippage, is more difficult with Cp* than with Cp.[11]  The fluorinated ligand, (trifluoromethyl)tetramethylcyclopentadienyl, C5Me4CF3, combines the properties of Cp and Cp*: it possesses the steric bulk of Cp* but has electronic properties similar to Cp, the electron-donation from the methyl groups being “canceled out” by the electron-accepting nature of the trifluoromethyl substituent.[12]  Its steric bulk stabilizes complexes with fragile ligands. Its bulk also attenuates intermolecular interactions, decreasing the tendency to form polymeric structures.  Its complexes also tend to be more soluble in non-polar solvents.  The methyl group in Cp* complexes can undergo C\u2013H activation leading to “tuck-in complexes”. Bulky cyclopentadienyl ligands are known that are far more sterically encumbered than Cp*.  Structure of tBu3C5H3, a prototypical bulky cyclopentadiene.See also[edit]References[edit]^ Elschenbroich, C.; Salzer, A. (1989). Organometallics: A Concise Introduction. VCH. p.\u00a047. ISBN\u00a09783527278183.^ De Vries, L. (1960). “Preparation of 1,2,3,4,5-Pentamethyl-cyclopentadiene, 1,2,3,4,5,5-Hexamethyl-cyclopentadiene, and 1,2,3,4,5-Pentamethyl-cyclopentadienylcarbinol”. J. Org. Chem. 25 (10): 1838. doi:10.1021\/jo01080a623.^ Threlkel, S.; Bercaw, J. E.; Seidler, P. F.; Stryker, J. M.; Bergman, R. G. (1993). “1,2,3,4,5-Pentamethylcyclopentadiene”. Organic Syntheses.; Collective Volume, vol.\u00a08, p.\u00a0505^ Fendrick, C. M.; Schertz, L. D.; Mintz, E. A.; Marks, T. J. (1992). Large-Scale Synthesis of 1,2,3,4,5-Pentamethylcyclopentadiene. Inorganic Syntheses. Vol.\u00a029. pp.\u00a0193\u2013198. doi:10.1002\/9780470132609.ch47. ISBN\u00a0978-0-470-13260-9.^ Yamamoto, A. (1986). Organotransition Metal Chemistry: Fundamental Concepts and Applications. Wiley-Interscience. p.\u00a0105. ISBN\u00a09780471891710.^ King, R. B.; Bisnette, M. B. (1967). “Organometallic chemistry of the transition metals XXI. Some \u03c0-pentamethylcyclopentadienyl derivatives of various transition metals”. J. Organomet. Chem. 8 (2): 287\u2013297. doi:10.1016\/S0022-328X(00)91042-8.^ Paquette, L. A.; Krow, G. R. (1968). “Electrophilic Additions to Hexamethyldewarbenzene”. Tetrahedron Lett. 9 (17): 2139\u20132142. doi:10.1016\/S0040-4039(00)89761-0.^ Criegee, R.; Gruner, H. (1968). “Acid-catalyzed Rearrangements of Hexamethyl-prismane and Hexamethyl-Dewar-benzene”. Angew. Chem. Int. Ed. Engl. 7 (6): 467\u2013468. doi:10.1002\/anie.196804672.^ Kang, J. W.; Mosley, K.; Maitlis, P. M. (1968). “Mechanisms of Reactions of Dewar Hexamethylbenzene with Rhodium and Iridium Chlorides”. Chem. Commun. (21): 1304\u20131305. doi:10.1039\/C19680001304.^ Kang, J. W.; Maitlis, P. M. (1968). “Conversion of Dewar Hexamethylbenzene to Pentamethylcyclopentadienylrhodium(III) Chloride”. J. Am. Chem. Soc. 90 (12): 3259\u20133261. doi:10.1021\/ja01014a063.^ Kuwabara, Takuya; Tezuka, Ryogen; Ishikawa, Mikiya; Yamazaki, Takuya; Kodama, Shintaro; Ishii, Youichi (2018-06-25). “Ring Slippage and Dissociation of Pentamethylcyclopentadienyl Ligand in an (\u03b7 5 -Cp*)Ir Complex with a \u03ba 3 – O , C , O Tridentate Calix[4]arene Ligand under Mild Conditions”. Organometallics. 37 (12): 1829\u20131832. doi:10.1021\/acs.organomet.8b00257. ISSN\u00a00276-7333.^ Gassman, Paul G.; Mickelson, John W.; Sowa, John R. (1992-08-01). “1,2,3,4-Tetramethyl-5-(trifluoromethyl)cyclopentadienide: a unique ligand with the steric properties of pentamethylcyclopentadienide and the electronic properties of cyclopentadienide”. Journal of the American Chemical Society. 114 (17): 6942\u20136944. doi:10.1021\/ja00043a065. ISSN\u00a00002-7863.     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