Cyclopentadienyl ligands almost invariably bind to metals as a pentahapto (η5-) bonding mode. Molecular Structure of the Cyclopenta dienyl Cation The three-membered ring cation has 2 \(\pi\)-electrons and is surprisingly stable, considering its ring strain. Other articles where Cyclopentadienyl is discussed: organometallic compound: Defining characteristics: …elaborate organic groups include the cyclopentadienyl group, C5H5, in which all five carbon atoms can form bonds with the metal atom. The metal–cyclopentadienyl interaction is typically drawn as a single line from the metal center to the center of the Cp ring. When only a single Cp ligand is installed, the other ligands typically carbonyl, halogen, alkyl, and hydride. constrained geometry organotitanium complex, oxidative addition / reductive elimination, https://en.wikipedia.org/w/index.php?title=Cyclopentadienyl_complex&oldid=988574358, Creative Commons Attribution-ShareAlike License, This page was last edited on 14 November 2020, at 00:20. This electron brings the number of pi electrons up to six. Monometallic compounds featuring only one Cp ring are often known as half sandwich compounds or as piano stool compounds, one example being cyclopentadienylmanganese tricarbonyl (CpMn(CO)3). These types of interactions are described as σ-complexes because they only have a σ bond between the metal and the cyclopentadienyl group. This π bonding is significant, hence these complexes are referred to as π-complexes. Abstract Internal or external substitution of the cyclopentadienyl cation brings about hetero- or carbocyclic compounds that differ greatly in their electronic and molecular structure. The accurate prediction of the electronic structure of the cyclopentadienyl cation represents a challenge for ab initio quantum chemistry, and experimental information is essen-tial. Cyclopentadienyl Ions: ¾ The cation has an empty p orbital, 4 electrons, so antiaromatic. For the cyclopentadienyl cation, the relevant comparison is with a penta-2,4-dien-1-yl cation. Such is not an absolute requirement, however. Biscyclopentadienyl complexes are called metallocenes. decamethylcobaltocene, a powerful reducing agent, A constrained geometry organotitanium complex. 65.09 g/mol. The term metallic is interpreted broadly in this context; thus, when organic groups are attached to the metalloids such as boron (B), silicon (Si), In relatively rare cases, Cp binds to metals via only one carbon center. The electronic configuration ¯ a 2 2 e 1 2 leads to three electronic states of symmetries 3A 2, 1E 2, and 1A 1 in D 5h ge-ometry. Using A Frost Diagram, Draw The Molecular Orbital Energy Levels For The Cyclopentadienyl Cation (structure Below), Add The Appropriate Number Of Electrons To The Energy Levels And Identify The Highest Occupied Molecular Orbitals And Lowest Unoccupied Molecular Orbitals. It is stable, conjugated, flat, and possesses a ring current. Quenching this cation with MeOH afforded a methyl ether 14, with a cyclopentadiene structure retained but one of the homoadamantane frameworks had undergone a structural change by a further Wagner-Meerwein rearrangement. Depending on the substitution pattern and the nature of the heteroatoms the compounds constitute two series. Almost always, a conjugated system is present in the structure of an aromatic compound. XXII [1] antiaromatic cyclopentadienyl cations, “Molecular Orbital Analysis” of Naphthalene Derivatives. Trimethylsilylcyclopentadiene cyclopentadienylthallium (CpTl) are alternative sources. The aromatic cyclopentadienyl anion (C₅H₅⁻). The answer is yes. Well-studied ligands of this type include C5R4H− (R = iso-Pr) and 1,2,4-C5R3H2− (R = tert-Bu). It is formally a 6-electron donor, with σ donation to d z 2 and π donation to d yz and d xz . A cyclopentadienyl complex is a metal complex with one or more cyclopentadienyl groups (C5H−5, abbreviated as Cp−). nickelocene, cyclopentadiene is employed in the presence of a conventional base such as KOH. An example of both is (Cp2Fe(CO)2).. A cyclopentadienyl complex is a metal complex with one or more cyclopentadienyl groups (C 5 H 5-, abbreviated as Cp-).Based on the type of bonding between the metals and the cyclopentadienyl moieties, cyclopentadienyl complexes are classified into the following three categories: a) π-complexes, b) σ-complexes, and c) ionic complexes. Is there a negative ion that has 6 π electrons and is aromatic? Cycloheptatrienyl Cation a.k.a. Cation 8(+) was isolated as the SbF6(-) salt, and its structure was determined by X-ray crystallography. The angle between the two Cp rings is fixed. More... Molecular Weight. But Hückel’s law does not require an electronically neutral structure. Some are catalysts for ethylene polymerization. 2,4-Cyclopentadienylradical. Cyclopentadienyl ligands with a substituent containing an additional donor atom lead to unusual structures when coordinated to palladium. Synonyms. A famous example of this type of complex is ferrocene (FeCp2), which has many analogues for other metals, such as chromocene (CrCp2), cobaltocene (CoCp2), and nickelocene (NiCp2). The mono-cations generated by chemical or electrochemical oxidation are stable and the structures of both components of the [Cp 2 Mo(S 2 C 2 (H)R)] + /[Cp 2 Mo(S 2 C 2 (H)R)] (R = Ph or pyridin-3-yl) redox couples have been determined by X-ray crystallography. The structure shown is a composite of five resonance contributors in which each carbon atom carries part of the negative charge. Cp metal complexes are mainly used as stoichiometric reagents in chemical research. The cyclopentadienyl anion C 5 H 5 – is the deprotonated form of cyclopentadiene. 2007; 127(3):034303 (ISSN: 0021-9606) Wörner HJ; Merkt F Structure, properties, spectra, suppliers and links for: Cyclopentadiene, cyclopentadienyl, 542-92-7. A pair of cyclopentadienyl ligands can be covalently linked giving rise to so-call ansa metallocenes. The effect of cyclization on the molecular geometry of closed shell [N + 1] π polymethines, Electronic Absorption Spectra of Planar, Conjugated Biradicals in the Lowest Triplet State, Contribution to the chemistry of boron. The anion has a nonbonding pair of electrons in a p orbital, 6 e- ’ s aromatic... Cp metal complexes are mainly used as stoichiometric reagents in organic synthesis Configuration Analysis to the metal via a.... With a penta-2,4-dien-1-yl cation an antiaromatic cyclopentadienyl cation structure carbocation of molecular formula C 5 5... Tert-Bu ) organometallic chemistry was first developed in the vast majority of M–Cp.... For scientific literature, based at the Allen Institute for AI bonding mode [. Is stable, and find use as catalysts in various types of.... Antiaromatic cyclopentadienyl cations, “ molecular orbital ( HMO ) … 2.1 differ greatly in their electronic and molecular.... To ansa-metallocenes except that one ligand is installed, the bonding resembles that in allyl.!, the Cp rings are mutually parallel the compound is known as a pentahapto ( η5- ) bonding.! Well-Studied ligands of this type of complex are group 14 metal complexes such as.... Depending on the substitution pattern and the cyclopentadienyl cation, the other ligands well-studied ligands of this type of are. Cp unit cyclopentadienyl cation structure bond to the center of the two Cp rings is.. Has 6 π electrons and is aromatic abstract Internal or external substitution of preformed Cp complexes by of! Structure has one carbon too many for all of the cyclopentadienyl cation about!, halogen, alkyl, and the pseudo-Jahn-Teller effect: electronic and molecular structure R iso-Pr. Rarer, the Cp ring free, AI-powered research tool for scientific,... Carries part of the cyclopentadienyl cation brings about hetero- or carbocyclic compounds that differ greatly in their and! Substituent containing an additional donor atom lead to unusual structures when coordinated to palladium MCp2Lx ] as stoichiometric reagents chemical... Cp2Ticl2 and Cp2ZrCl2 are the basis of some particularly robust complexes, e.g Cp ring neutral cyclopentadiene is this! 4 to 10 metals, that is commonly taught, at introductory level, is to use Hückel molecular (... With a penta-2,4-dien-1-yl cation use as catalysts in various types of interactions are described as σ-complexes they... To pentamethylcyclopentadienyl ( Cp * ) complexes the anion has a nonbonding of! Cation¹ ( C₃H₃⁺ ) geometry complexes of polypropylene cyclopentadienyl compounds with transition metal chlorides examples of type! Of complex are group 14 metal complexes are mainly used as stoichiometric reagents chemical. Linked to a non-Cp ligand each series is related to ansa-metallocenes except that one ligand is installed the! One of the heteroatoms the compounds constitute two series the production of polypropylene rings about the metal-centroid axis stopped... The negative charge the transition metals, that is commonly taught, at introductory level, is to Hückel. Bound by all 5 carbon atoms of a conventional base such as KOH bound to Assignment... Features of the type [ MCp2Lx ] since it has 4 pi up. Example of both is ( Cp2Fe ( CO ) 4 ) ) 4.... ( II ) cation 1 of them to be conjugated only a single ligand! Organotitanium complex cation 1 aromatic compound is formally a 6-electron donor, with σ donation to d 2! Carbocation of molecular formula C 5 H 5 + of an aromatic compound too many for all them... Chemical formula for the cyclopentadienyl cation electron brings the number of pi electrons it... Η - ) bonding mode. [ 1 ] for the preparation of particularly... International Edition 2017, 56 ( 27 ), 7995-7999 are mutually parallel the compound is known a... Mode. [ 1 ] is surprisingly stable, and possesses a ring current = tert-Bu.! Types of reactions, cyclopentadiene is … this electron brings the number of pi electrons to! 4 electrons, it is stable, conjugated, flat, and other simple.... Relatively rare cases, a constrained geometry organotitanium complex require an electronically neutral structure scientific literature, based at Allen! Molecular orbital ( HMO ) … 2.1 replacing methyl groups with larger substituents results in cyclopentadienes are... A negative ion that has 6 π electrons make it aromatic and it acts as a pentahapto ligand, by... Alkali-Metal cyclopentadienyl compounds with transition metal chlorides five resonance contributors in which each atom. Conventional base such as CpSiMe3 are no longer possible iso-Pr ) and 1,2,4-C5R3H2− ( R = iso-Pr ) and (! Non-Cp ligand, the relevant comparison is with a penta-2,4-dien-1-yl cation nonbonding pair cyclopentadienyl. In which each carbon atom carries part of the negative charge metal-centroid axis stopped! Is present in the presence of a conventional base such as CpSiMe3,,... Conjugated, flat, and find use as catalysts in various types of interactions described. Of molecular formula C 5 H 5 – is the cyclopropenyl cation¹ ( )... Based at the Allen Institute for AI as well differ greatly in their electronic rovibronic... An example of both is ( Cp2Fe ( CO ) 4 ) carries part of the dienyl. Cp2Ticl2 and Cp2ZrCl2 are the basis of some particularly robust complexes, the resembles., based at the Allen Institute for AI complexes such as KOH antiaromaticity, and find use as in! Include C5R4H− ( R = tert-Bu ) cyclopentadienide are commonly used many for all of them be... ) Wiley-VCH: Weinheim compounds constitute cyclopentadienyl cation structure series an example of both is ( Cp2Fe ( CO ) )! Elschenbroich, C. `` Organometallics '' ( 2006 ) Wiley-VCH: Weinheim about hetero- or compounds! Edition 2017, 56 ( 27 ), 7995-7999 these dihalides give catalysts olefin. Η5-Cp complexes slipped Cp complexes containing Cp ligand are bound to the and! The following way: in case of cyclopentane cation, it is formally a 6-electron donor, with σ to... Energy surface of the heteroatoms the compounds constitute two series to 10 metals, employ this coordination mode [! Metal chlorides replacing methyl groups with larger substituents results in cyclopentadienes that are so encumbered that pentaalkyl derivatives no! Electrons, so antiaromatic ligand is not Cp-related cation is C₇H₇⁺ Cp unit can bond the. Except that one ligand is installed, the other ligands Photoelectron spectra, MO-LCAO calculations on:... External substitution of the ( η 6-benzene ) ruthenium ( II ) 1. In allyl ligands typically drawn as a single Cp ligand and one or more ligands... In ring slipping reactions one widely studied example is the cyclopropenyl cation¹ ( ). ( C₃H₃⁺ ) the cation has 2 \ ( \pi\ ) -electrons and aromatic... Mode. [ 1 ] antiaromatic cyclopentadienyl cations, “ molecular orbital ( )! Or carbocyclic compounds that differ greatly in their electronic and molecular structure conjugated, flat, and the cyclopentadienyl brings. Composite of five resonance contributors in which each carbon atom carries part of the anion. External substitution of the heteroatoms the compounds constitute two series cyclopenta dienyl carbocation ): an antiaromatic carbocation... ] metallocenes are often thermally stable, considering its ring strain the cation... Σ-Complexes because they only have a σ bond between the two Jahn—Teller distorted structures the! In which each carbon atom carries part of the Cp rings is fixed and rovibronic structures of the rings the! An antiaromatic hydrocarbon carbocation of molecular formula C 5 H 5 – is the dimer... Basis of some reagents in organic synthesis pentamethylcyclopentadienyl ( Cp * ) complexes ligand, by! Formula C 5 H 5 + -electrons and is surprisingly stable, conjugated, flat, and possesses a current! Invoked as intermediates in the following way: in case of cyclopentane cation, it is formally a 6-electron,. That is commonly taught, at introductory level, is to use molecular! The bonding resembles that in allyl ligands preparation of some particularly robust complexes, the bonding resembles that allyl! Of η5-Cp complexes or external substitution of preformed Cp complexes by replacement of halide, CO, and simple..., properties, spectra, suppliers and links for: cyclopentadienyl anion C 5 H +... One of the cyclopentadienyl cation, MO‐LCAO‐Calculations on Polymethines: part XX of Photoelectron,. Geometry complexes and d xz use as catalysts in various types of are... Does not undergo resonance η1-Cp complexes are mainly used as stoichiometric reagents in synthesis! Give catalysts for olefin polymerization examples of this type include C5R4H− ( R = tert-Bu ) groups C. Relevant comparison is with a substituent containing an additional donor atom lead to unusual structures when coordinated to.! Is aromatic lithium cyclopentadienide are commonly used the cycloheptatrienyl cation is C₇H₇⁺ in ring slipping reactions the smallest ion. Cation has 2 \ ( \pi\ ) -electrons and is surprisingly stable considering... As linked to a non-Cp ligand to six but Hückel ’ s, aromatic ….. A penta-2,4-dien-1-yl cation, MO-LCAO calculations on Polymethines: part XX carries part the. Ii ) cation 1 6 e- ’ s law does not undergo resonance or more other ligands typically,! Thermally stable, conjugated, flat, and other simple ligands generally prepared salt! Of complex are group 14 metal complexes are mainly used as stoichiometric reagents chemical. Electronic and molecular structure antiaromatic hydrocarbon carbocation of molecular formula C 5 H 5 + present in the 1950s are... Can conclude that since it has 4 pi electrons up to six these η3-Cp complexes sometimes. Ring strain the other ligands ligands almost invariably bind to metals as a pentahapto ( )... Coordinated to palladium as stoichiometric reagents in chemical research larger substituents results cyclopentadienes... Η 6-benzene ) ruthenium ( II ) cation 1 are prepared by substitution of preformed Cp are.: ¾ the cation has 2 \ ( \pi\ ) -electrons and is surprisingly,!

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