Ylide Anions Research Articles

Electrochemical Oxidation of [1-X-12-I-CB11Me10-] Anions: Formation of Borenium Ylides [12-Dehydro-1-X-CB11Me10] and Iodonium Ylide Anions [{12-(1-X-CB11Me10-)}2I+

Cyclic voltammograms of 12-iodinated icosahedral carborane anions [1-X-12-I-CB11Me10-] (X = H, CH3, C2H5, C3H7, C4H9, C6H13, and COOCH3) show two one-electron anodic oxidation peaks at the Pt electrode in liquid SO2. Oddly, the first is irreversible and the second partially reversible. Mass spectrometry of the principal anionic product of preparative anodic oxidation of [1-H-12-I-CB11Me11-], identical with the anionic product of its reaction with [Et3Si-H-SiEt3]+ and/or Et3Si+, allows it to be identified as the iodonium ylide anion [{12-(1-H-CB11Me10-)}2I+]. Its reversible oxidation to a neutral ylide radical [{12-(1-H-CB11Me10•)}{12-(1-H-CB11Me10-)}I+] is responsible for the second peak. A DFT geometry optimization suggests that both the ylide anion and the ylide radical are very crowded and have an unusually large C-I-C valence angle of ∼132°; they are the first compounds with two bulky highly methylated CB11 cages attached to the same atom. Molecular iodine is another product of the electrolysis. We propose an electrode mechanism in which initial one-electron oxidation of [1-X-12-I-CB11Me10-] is followed by a transfer of an iodine atom from the B-I bond to SO2 to yield a weakly bound radical ISO2• which disproportionates into SO2 and I2. The other product is the borenium ylide [12-dehydro-1-X-CB11Me10], which has a strongly Lewis acidic naked vertex in position 12 that rapidly adds to another [1-X-12-I-CB11Me10-] anion to form the observed stable ylide anion [{12-(1-X-CB11Me10-)}2I+]. In acetonitrile, where it presumably exists as a solvent adduct, [12-dehydro-1-X-CB11Me10] has been trapped with H2O and, to a small extent, with MeOH, but not with several other potential trapping agents.

Cyclic Trinuclear Gold(I) Clusters with N,N and Unusual C,C Mixed-Ligand Bridges.

Three crystalline trinuclear gold(I) clusters, [Au3f2y] (1), [Au3fy2] (2), and [Au3y3] (3), where f = N,N'-bis(2,6-dimethylphenyl)methanimidamidate and y = dimethylendiphenylphosphinate, exhibit bridges from the N,N-formamidinate and/or from the ylide anion ligand whose P-methylene groups chelate in an unusual fashion, where the chelate CPC unit is perpendicular to the trigonal plane of the metal atoms. Assemblies 1 and 2 are the first gold(I) trinuclear clusters featuring mixed-ligand bridges from different N,N and C,C donors; 3 is a previously unknown homoleptic ylide anion cyclic trinuclear assembly. Formamidinate bridges in 1 and 2 connect gold(I) atoms at aurophilic distances of 3.084(2) and 3.0543(4) Å, whereas an out-of-plane (perpendicular) P-ylide anion bite produces AuI-AuI distances of as large as 3.900(2) Å in 3. The crystal space groups for 1 and 2 are triclinic P1̅ and that for 3 is monoclinic P21/c, with Z = 2 for 1 and 2 and Z = 4 for 3. Compounds are synthesized under Schlenk conditions at -20 °C in toluene by reacting the proper ratios of the gold(I) formamidinate [Au2f2] with the phosphorus ylide [Hy] under basic conditions (KOH), followed by extraction with ether. This synthesis also produces a dinuclear cation, [Au2f(Hy)2]+, previously reported by our group. A neutral mixed-ligand dinuclear complex, [Au2fy], was not observed. Under UV light, 1 and 2 display a bright-green luminescence at room temperature and in frozen methyltetrahydrofuran solutions under liquid nitrogen, with microsecond lifetimes. All three complexes 1-3 are characterized by their X-ray crystal structures, 1H NMR, IR, UV-visible, and luminescence spectroscopies, and elemental analysis.

New Synthesis of 3-Trifluoromethylpyrroles by Condensation of Mesoionic 4-Trifluoroacetyl-1,3-oxazolium-5-olates with Phosphorus Ylides

Mesoionic 4-trifluoroacetyl-1,3-oxazolium-5-olates (1), obtained from the reaction of N-acyl-N-alkylglycines with trifluoroacetic anhydride, react with phosphorus ylides to give β-trifluoromethylpyrroles (2) in good yields. The novel ring transformations of 1 into 2 occur via an initial attack of the ylide anions on the C-2 position of the ring.

Reactivity of Aldehydes with Semi‐Stabilized Arsonium Ylide Anions: Synthesis of Terminal (E)‐1,3‐Dienes.

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Reactivity of Aldehydes with Semi‐Stabilised Arsonium Ylide Anions: Synthesis of Terminal (E)‐1,3‐Dienes

A study of the reactivity of semi-stabilised arsonium ylide anions in olefination reactions is presented. The different ylide anions were generated by the addition of nBuLi to various arsonium halide derivatives: [Ph(2)As(R)R'](+)X(-), where R and R' are methyl, allyl, prenyl or benzyl groups. By using diallyldiphenylarsonium bromide (R=R'=allyl) an olefination protocol was optimised allowing the efficient transformation of aliphatic aldehydes into terminal 1,3-dienes with a high selectivity for the E isomer (E/Z ratios ranging from 90:10 to 97:3). The olefination reactions of aldehydes with dissymmetric arsonium halides (R not equal R') are very chemoselective; with arsonium ylide anions the benzyl moiety is more reactive than the allyl moiety which is much more reactive than prenyl and methyl groups. Based on the experimental results, a mechanism is proposed for the reaction.

A Convenient Stereocontrolled Route to Trifluoromethylated Penta‐2E,4E‐ or 2Z,4E‐dienenitriles.

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A Convenient Stereocontrolled Route to Trifluoromethylated Penta-2E,4E- or 2Z,4E-dienenitriles

The phosphoryl-stabilized carbanions 2, generated from the corresponding phosphonates and lithium diisopropylamide in tetrahydrofuran, were used to add regiospecifically to [(trifluoroacyl)cyanomethylenetriphenylphosphorane] (1) forming ylide anions 3. After protonation and elimination of triphenylphosphine oxide from 3, trifluoromethylated cyanoallylphosphonates 4 were obtained in 74-95% yields with high Z-stereoselectivity (4a-c) or E-stereoselectivity (4d-h) depending upon the structure of the phosphoryl-stabilized carbanions 2 used. The E- and Z-isomers of 4 could be separated conveniently by column chromatography. Treatment of Z-4 or E-4 with sodium hydride gave an anion which reacted with aldehydes affording the trifluoromethylated penta-2E,4E- or 2Z,4E-dienenitriles exclusively or predominantly in 52-71% yields. Their structures were determined by X-ray crystallographic analysis.

ChemInform Abstract: Novel Conversion of E Stereoselectivity to Z Stereoselectivity in Trifluoromethylated α,β‐Unsaturated Esters and Nitriles by Way of O‐Methylation of an Ylide Anion.

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Novel conversion of E stereoselectivity to Z stereoselectivity in trifluoromethylated α,β-unsaturated esters and nitriles by way of O-methylation of an ylide anion

A stereocontrolled synthesis of (Z)-trifluoromethylated α,β-unsaturated esters and nitriles by way of O-methylation of an ylide anion is described.

Synthesis and comparative chemistry of the early-late transition metal heterobimetallacycles CpCp′Ta(CH 2) 2Ir(CO)(L) and their main-group element-late transition metal analogues R 2P(CH 2) 2Ir(CO)(L)

The synthesis of two tantalum-iridium heterodinuclear complexes formed by the reaction of CpCp′Ta(CH 2)(CH 3) with IndIr(CO) 2 is presented (Cp′ Cp ( 1a); indenyl ( 1b)). An X-ray diffraction study of the compound (Ind)CpTa(CH 2) 2Ir(CO) 2 was performed: the Ta(CH 2) 2Ir ring is planar and the TaIr bond length is 2.858(1) Å. These compounds react with phosphines to form substitution and addition products. The crystal structure of the PEt 3 adduct Cp 2Ta(CH 2) 2Ir(CO) 2(PEt 3) ( 2) is presented; the geometry about the iridium center of 2 is midway between a square-based pyramid and a trigonal bipyramid, and the TaIr bond length is 2.881(1) Å. Compound 1a reacts with MeI to form the six-coordinate iridium oxidative addition product Cp 2Ta(CH 2) 2Ir(CO) 2(CH 3)I. The compound Cp 2Ta(CH 2) 2Ir(CO)(PPh 3) ( 3) reacts with MeI in an analogous manner ( k 2nd  7.61 ± 0.43 M −1 s −1, THF, −5 °C). In order to assess the effect of the early metal on the chemistry at the late transition metal center, the chelating phosphorus ylide analogues R 2P(CH 2 )2Ir(CO)(PPh 3) (RPh ( 6a), Me ( 6b)) were synthesized by treatment of the ylide anion, R 2P(CH 2) 2Li with Vaska's complex (PPh 3) 2Ir(CO)Cl. An X-ray diffraction study performed on 6a showed that the Ir(CoH 2) 2P metallacycle, in contrast to that of the Ta-Ir compounds, is non-planar. The ylide P-Ir distance 2.746(1) Å is beyond bonding interaction. Compounds 6a ( k 2nd  7.55 ± 0.30 M −1 s −1, THF, −5 °C) and 6b ( k 2nd  17.9 ± 1.4 M −1 s −1, THF, −5 °C) react with CH 3I in a fashion analogous to that of the TaIr complexes. Unlike compound 3, both 6a and 6b are highly fluxional in solution due to the dissociation of the PPh 3 ligand from the Ir center. In addition, the metallacycle undergoes rapid ring inversion in solution, even at −90 °C. These studies suggest the early metal fragment can act as an electron sink and source for the late transition metal fragment through a direct TaIr bond interaction.

ChemInform Abstract: Wittig Reactions of Ylide Anions Derived from Stabilized Ylides.

ChemInformVolume 20, Issue 49 Preparative Organic Chemistry ChemInform Abstract: Wittig Reactions of Ylide Anions Derived from Stabilized Ylides. E. G. MCKENNA, E. G. MCKENNA Dep. Chem., Queen's Univ., Belfast BT9 5AG, Northern IrelandSearch for more papers by this authorB. J. WALKER, B. J. WALKER Dep. Chem., Queen's Univ., Belfast BT9 5AG, Northern IrelandSearch for more papers by this author E. G. MCKENNA, E. G. MCKENNA Dep. Chem., Queen's Univ., Belfast BT9 5AG, Northern IrelandSearch for more papers by this authorB. J. WALKER, B. J. WALKER Dep. Chem., Queen's Univ., Belfast BT9 5AG, Northern IrelandSearch for more papers by this author First published: December 5, 1989 https://doi.org/10.1002/chin.198949103Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume20, Issue49December 5, 1989 RelatedInformation

Wittig reactions of ylide anions derived from stabilised ylides

Ester- and nitrile-stabilised ylide anions are more reactive than the corresponding ylides and react with aldehydes and ketones to give alkenes in good yields; the reactivity of stabilised triphenylphosphonium ylides is greatly increased by the replacement of one phenyl substituent.

Synthesis of Nitriles via the Ylide Anion of Sodium Cyanotriphenylphosphoranylidenemethanide

A convenient access to nitriles having a variety of extremely different structures is provided by the ylide anion 1, which is isolable as the sodium salt. By reaction with alkyl halides RX, 1 can be converted into cyclic α,β-unsatu-rated nitriles such as 2; the “dienyl cyanides” 3 and alkynyl cyanides RCCCN are obtainable from 1 by reaction with aldehydes RCHO and esters RCOOR', respectively.

New ylide anions. A vinyl anion equivalent for substituted fumarate esters

A new type of ylide anion is reported which upon alkylation and elimination of triphenylphosphine serves as a vinyl anion equivalent.

Alkyl complexes of scandium(III), titanium(III) and vanadium(III) derived from phosphorus ylide anions

Alkyl complexes of scandium(III), titanium(III) and vanadium(III) derived from phosphorus ylide anions