| 词条 | Pentamethylcyclopentadiene | |||||||||||||||
| 释义 |
| Verifiedfields = changed | Watchedfields = changed | verifiedrevid = 418038654 | Name = Pentamethylcyclopentadiene | ImageFile = Pentamethylcyclopentadien.svg | ImageSize = 135 | ImageAlt = Skeletal formula of pentamethylcyclopentadiene | ImageFile1 = Pentamethylcyclopentadiene molecule ball.png | ImageSize1 = 160 | ImageAlt1 = Ball-and-stick model of the pentamethylcyclopentadiene molecule |Section1={{Chembox Identifiers | CASNo_Ref = {{cascite|correct|??}} | CASNo = 4045-44-7 | SMILES = CC1=C(C)C(C)C(C)=C1C | PubChem = 77667 | ChemSpiderID_Ref = {{chemspidercite|changed|chemspider}} | ChemSpiderID = 70069 | InChI = 1/C10H16/c1-6-7(2)9(4)10(5)8(6)3/h6H,1-5H3 | InChIKey = WQIQNKQYEUMPBM-UHFFFAOYAI | StdInChI_Ref = {{stdinchicite|changed|chemspider}} | StdInChI = 1S/C10H16/c1-6-7(2)9(4)10(5)8(6)3/h6H,1-5H3 | StdInChIKey_Ref = {{stdinchicite|changed|chemspider}} | StdInChIKey = WQIQNKQYEUMPBM-UHFFFAOYSA-N |Section2={{Chembox Properties | Formula = C10H16 | MolarMass = 136.24 g/mol | Solubility = Sparingly soluble | BoilingPtC = 55 to 60 | BoilingPt_notes = at {{convert|13|mmHg|kPa|abbr=on}} |Section7={{Chembox Hazards | FlashPtC = 114 }} 1,2,3,4,5-Pentamethylcyclopentadiene is a cyclic dialkene 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* (to signify the five methyl groups radiating from the periphery of this ligand as in a five-pointed star). In contrast to less-substituted cyclopentadiene derivatives, Cp*H is not prone to dimerization. SynthesisPentamethylcyclopentadiene 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] 2 MeCH=C(Li)Me + MeC(O)OEt → (MeCH=C(Me))2C(OLi)Me + LiOEt (MeCH=C(Me))2C(OLi)Me + H+ → Cp*H + H2O + Li+ Organometallic derivativesCp*H is a precursor to organometallic compounds containing the {{chem|C|5|Me|5|−}}ligand, commonly called Cp*−.[5]
Some representative reactions leading to such Cp*–metal complexes follow:[6] Cp*H + C4H9Li → Cp*Li + C4H10 Cp*Li + TiCl4 → Cp*TiCl3 + LiCl Some Cp* complexes are prepared using silyl transfer:
Some Cp* complexes were originally prepared using hexamethyl Dewar benzene as the precursor. This method was traditionally used for [Rh(C5Me5)Cl2]2, but has been discontinued with the increased commercial availability of Cp*H. 2 Cp*H + 2 Fe(CO)5 → [Cp*Fe(CO)2]2 + H2 + CO For the related Cp complex, see cyclopentadienyliron dicarbonyl dimer. An 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. 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 of Cp* with CpComplexes of pentamethylcyclopentadienyl differ in several ways from the more common cyclopentadienyl (Cp) derivatives. Being more electron-rich, Cp* is a stronger donor and is less easily displaced from the metal.{{citation needed|date=January 2017}} 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–H activation leading to "tuck-in complexes". See also
References1. ^{{cite book|last1=Elschenbroich |first1=C. |last2=Salzer |first2=A. |title=Organometallics: A Concise Introduction |date=1989 |page=47 |isbn=9783527278183| publisher=VCH}} 2. ^{{cite journal | first= L. |last=De Vries | title= 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 | journal = J. Org. Chem. | volume = 25 | year = 1960 | pages = 1838 | doi = 10.1021/jo01080a623 | issue = 10}} 3. ^{{OrgSynth | first1= S. |last1=Threlkel |first2=J. E. |last2=Bercaw |first3=P. F. |last3=Seidler |first4=J. M. |last4=Stryker |first5=R. G. |last5=Bergman | prep = cv8p0505 | title = 1,2,3,4,5-Pentamethylcyclopentadiene | collvol = 8 | collvolpages = 505 | year = 1993}} 4. ^{{cite journal | last1= Fendrick |first1=C. M. |last2=Schertz |first2=L. D. |last3=Mintz|first3=E. A. |last4=Marks |first4=T. J. | title = Large-Scale Synthesis of 1,2,3,4,5-Pentamethylcyclopentadiene | journal = Inorganic Syntheses | volume = 29 | pages = 193–198 | year = 1992 | doi = 10.1002/9780470132609.ch47 | series = Inorganic Syntheses | isbn = 978-0-470-13260-9}} 5. ^{{cite book|last=Yamamoto|first=A. |title=Organotransition Metal Chemistry: Fundamental Concepts and Applications |date=1986 |page=105 |isbn=9780471891710 |publisher=Wiley-Interscience}} 6. ^{{cite journal | title = Organometallic chemistry of the transition metals XXI. Some π-pentamethylcyclopentadienyl derivatives of various transition metals | first1= R. B. |last1=King|first2= M. B.|last2= Bisnette | journal = J. Organomet. Chem. | volume = 8 | year = 1967 | pages = 287–297 | doi = 10.1016/S0022-328X(00)91042-8 | issue = 2}} 7. ^{{cite journal |last1= Paquette|first1= L. A.|last2= Krow|first2= G. R.|year= 1968|title= Electrophilic Additions to Hexamethyldewarbenzene|journal= Tetrahedron Lett.|volume= 9|issue= 17|pages= 2139–2142|url= |doi= 10.1016/S0040-4039(00)89761-0}} 8. ^{{cite journal |last1= Criegee|first1= R.|last2= Gruner|first2= H.|year= 1968|title= Acid-catalyzed Rearrangements of Hexamethyl-prismane and Hexamethyl-Dewar-benzene|journal= Angew. Chem. Int. Ed. Engl.|volume= 7|issue= 6|pages= 467–468|url= |doi= 10.1002/anie.196804672}} 9. ^{{cite journal |last1= Kang|first1= J. W.|last2= Mosley|first2= K.|last3= Maitlis|first3= P. M.|authorlink3=Peter Maitlis|year= 1968|title= Mechanisms of Reactions of Dewar Hexamethylbenzene with Rhodium and Iridium Chlorides|journal= Chem. Commun.|issue= 21|pages= 1304–1305|url= |doi= 10.1039/C19680001304}} 10. ^{{cite journal |last1= Kang|first1= J. W.|last2= Maitlis|first2= P. M.|authorlink2=Peter Maitlis|year= 1968|title= Conversion of Dewar Hexamethylbenzene to Pentamethylcyclopentadienylrhodium(III) Chloride|journal= J. Am. Chem. Soc.|volume= 90|issue= 12|pages= 3259–3261|url= |doi= 10.1021/ja01014a063}} 2 : Cyclopentadienes|Ligands |
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