The First Nonclassical Distonic Ion (original) (raw)
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Journal of the American Society for Mass Spectrometry, 2006
By Yates, Bouma, and Radom's definition, distonic radical ions are those formally arising by ionization of diradicals or zwitterionic molecules (including ylides). These ions differ, therefore, from conventional radical ions by displaying the charge site and unpaired electron site (spin) localized mandatorily on separate atoms or group of atoms; that is, these sites are separated in all of their major resonance forms. Many conventional radical ions with a major resonance form in which charge and spin sites reside formally on the same atom or group of atoms display, however, high degree of discretionary (non-mandatory) charge-spin separation. By analogy with the metal/metalloid terminology, we propose that these distonic-like radical ions be classified as distonoid ions. Radical ions would, therefore, be divided into three sub-classes: conventional, distonic, and distonoid ions. B3LYP/6-311 ϩ G(d,p) calculations for a proof-of-principle set of radical cations are used to demonstrate the existence of many types of distonoid ions with a high degree of discretionary charge-spin separation. Reliable calculations are indispensable for probing distonoid ions, since an ion that was expected to be distonoid (by the analysis of its resonance forms) is shown by the calculations to display a characteristic conventional-ion electronic distribution. Similarly to many distonic radical ions, and in sharp contrast to a conventional radical ion (ionized 1,4-dioxane), the gas-phase intrinsic bimolecular reactivity with selective neutrals of a representative distonoid ion, ionized 2-methylene 1,3-dioxolane, is found to include dual ion-radical type reactions.
Bonding, proton transfer, and diradical stabilization in phosphonium ylides
Journal of the American Chemical Society, 1970
The phosphorus-carbon bond of phosphonium ylides is studied with semiempirical molecular orbital calculations. The primary effect of the inclusion of 3d orbitals on phosphorus is the anticipated electron transfer from the ylide carbon to the 3d orbitals, with an accompanying increase in P-C bond order. A novel effect of some significance is the hyperconjugative a-type interaction of CHZ orbitals in a model H3PCHz with a P 3d orbital of the appropriate symmetry. Intermolecular and intramolecular mechanisms for proton transfer in (CH3)3PCH2 are studied. A concerted hydrogen switch involving two molecules is calculated to possess a high activation energy. The potential surface for a concerted intramolecular hydrogen migration leads to a transition state best described as a pentavalent phosphorus derivative. Carbon diradicals should be stabilized by intervening phosphorus or other second-row atoms. This type of stabilization is studied for a hypothetical CH2PR3CH2. Such species are potential singlet states and should possess barriers to rotation of CHZ groups but not of the PRa moiety.
Distonic ions of the �ate� class
Journal of the American Society For Mass Spectrometry, 1999
The gas phase synthesis, structure, and reactivity of distonic negative ions of the "ate" class are described. "Ate"-class negative ions are readily prepared in the gas phase by addition of neutral Lewis acids, such as BF 3 , BH 3 , and AlMe 3 , to molecular anions, carbene negative ions, and radical anions of biradicals. The ions contain either localizedor delocalized -type radical moieties remote from relatively inert borate and aluminate charge sites. The free radical reactivity displayed by these ions appears to be independent of the charge site. As an example, the distonic alkynyl radical (⅐C'CBF 3 Ϫ ) is highly reactive and undergoes radical coupling reactions with NO 2 , NO, H 2 CACH-CN, and H 2 CACH-CH 3 . Radical-mediated group and atom transfers are observed with O 2 , CS 2 , and CH 3 SSCH 3 . Furthermore, H-atom abstraction reactions are observed, in accordance with the predicted high C-H bond strength of this species [DH 298 (H-C 2 BF 3 Ϫ ) ϭ 130.8 kcal mol Ϫ1 ]. High level ab initio molecular orbital calculations on the prototype "ate"-class distonic ion ⅐ CH 2 BH 3
Ambident Reactivity of Acetyl- and Formyl-Stabilized Phosphonium Ylides
Journal of the American Chemical Society, 2016
The kinetics and mechanism of the reactions of formyl-stabilized ylide Ph3P═CHCHO (1) and acetyl-stabilized ylide Ph3P═CHCOMe (2) with benzhydrylium ions (Ar2CH(+), 3) were investigated by UV-vis and NMR spectroscopy. As ambident nucleophiles, ylides 1 and 2 can react at oxygen as well as at the α-carbon. For some reactions, it was possible to determine the second-order rate constant for O-attack as well as for C-attack and to derive the nucleophile-specific parameters N and sN according to the correlation lg k (20 °C) = sN(E + N) for both nucleophilic sites. Generally, O-attack of benzhydrylium ions is faster than C-attack. However, the initially formed benzhydryloxyvinylphosphonium ions can only be observed by NMR spectroscopy when benzhydryl cations with high Lewis acidity are employed. In other cases, rearrangement to the thermodynamically more stable products arising from C-attack occurs. The results derived from our investigations are employed to rationalize the behavior of am...
Are RR′C–PR″(BH3)2 ‘electron poor’ phosphorus ylides?— an ab initio–NMR study †
Journal of the Chemical Society, Perkin Transactions 2, 2000
The parent RRЈC-PRЉ(BH 3) 2 , 3 (R, RЈ, RЉ = H), has no minimum geometry with ylide structure. In contrast to 'normal' ylides, RRЈC-PRЉ 3 , which are destabilised when the substituents (R, RЈ) have π donor character, the investigated RRЈC-PRЉ(BH 3) 2 require at least one amino group to form a stable ylidic structure (e.g. 4NH with R = NH 2 , RЈ = H, and RЉ = H). Without π donor substituents the molecules lack a tautomerisation barrier for the hydroborylation (RRЈC᎐ ᎐ PH(BH 3)-BH 2 HЈ→(RRЈHЈC-PH(BH 3)᎐ ᎐ BH 2). Compound 6, cyclo-1-(C-PH(BH 3) 2)-2,5-(NH) 2-3,4-(CH) 2 , is a model for the ylide recently obtained by Arduengo. Analysis of the electronic structure confirms his suggestion that a considerable delocalisation from the carbene moiety into the 'electron poor' PRЉ(BH 3) 2 group occurs. This electron delocalisation is reflected by the partial charge of the ylide group (Ϫ0.50 in 4HN, Ϫ0.51 in 4NN, and Ϫ0.85 in 6) which is negative (positive in 'normal' ylides). The term 'inverse ylides' could express this special bonding situation.
The Journal of Organic Chemistry, 2001
We report the synthesis of a new series of cyclophanes 11a-d by ester-forming macrocyclization reactions of diol 9 with the dicarbonyl chloride derivatives of benzene, thiophene, ferrocene, and diphenyl ether, 10a-d, respectively. Compounds 11a-d display a two-electron, quasireversible oxidation wave in the cyclic voltammogram to yield the dication species at E ox pa) 0.70-0.72 V (for 11a-c) and 0.47 V (for 11d) (vs Ag/AgCl in acetonitrile). The raised oxidation potentials for 11a-c reflect the reduced stability of the twisted dication structure within the steric constraints of the smaller cyclophanes. Consistent with this, the value of ∆E (defined as E ox pa-E ox pc) decreases (i.e., reversibility of the oxidation process increases) in the sequence 11d > 11c > 11a > 11b as the bridging chain becomes shorter. X-ray crystal structures are reported for compounds 11a-d and the dication salt 11d 2+ (I 3-) 2 ‚(CH 2 Cl 2) 2.25. For 11a-d the typical saddle-shaped conformation of the 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene moiety is observed, with the strain imposed by the cyclophane ring being accommodated in the structure of the bridging unit. In the dication 11d 2+ both dithiolium rings are planar and the anthracene unit is essentially aromatic, with the conformation of the bridge basically the same as in neutral 11d.
Angewandte Chemie International Edition, 2007
We have previously developed a strategy for the preparation of heterometallic main-group imido (RN 2À ) and phosphinidene (RP 2À ) compounds involving stepwise deprotonation of REH 2 (E = N,P) with alkali-metal organometallics (for example nBuLi), followed by reaction with M(NMe 2 ) n (M = As, Sb, Bi, n = 3; Sn n = 2; Scheme 1). Recently, however, we have recognized the behavior of this type of mixed-metal system as superbases. This effect was first apparent in the reaction of MesPH 2 (Mes = 2,4,6-Me 3 C 6 H 2 ) with Sn(NMe 2 ) 2 /PhCH 2 Na, which gives the unusual stannate ion [Sn{P(2-CH 2 -4,6-Me 2 C 6 H 2 )}{PMes}] 3À [3] as a result of deprotonation of a PH 2 group and an ortho-CH 3 group. Remarkably, quadruple deprotonation of the PH 2 and NH 2 groups occurs in 1-NH 2 -2-PH 2 -C 6 H 4 (LH 4 ) using a similar Sn(NMe 2 ) 2 /nBuLi mixture, giving the paramagnetic complex [({(L)Sn-(NMe 2 )Li·THF}{(L)SnLi·3 THF}Sn) 2 ] containing the L 4À tetraanion and LC 3À radical. Herein we report the reaction of 1,2-(PH 2 ) 2 C 6 H 4 with Sb(NMe 2 ) 3 /nBuLi, which results in the complete deprotonation of the PH 2 groups, giving the 6p-aromatic anion [1,2-C 6 H 4 P 2 Sb] À . Upon one-electron reduction, the [1,2-C 6 H 4 P 2 Sb] 2 4À tetraanion is formed. As established from DFT calculations, this highly charged, Sb À Sb-bonded distibane is best described as a dimer of two 7p-[1,2-C 6 H 4 P 2 Sb]C 2À radicals (Scheme 2 a) and is valence-isoelectronic with the important class of sulfur/nitrogen-based thiazolyl radicals (Scheme 2 b). Lithiation of 1,2-(PH 2 ) 2 C 6 H 4 (1 equiv) with nBuLi (2 equiv) in tmeda (tmeda = Me 2 NCH 2 CH 2 NMe 2 ) followed by reaction with Sb(NMe 2 ) 3 (0.67 equiv) gives [Li-(tmeda) 2 ] + [1,2-C 6 H 4 P 2 Sb] À (1) after crystallization from THF/tmeda. However, black crystals of [{1,2-C 6 H 4 P 2 Sb} 2 {Li-(tmeda)} 4 ] (2) are obtained if this reaction is undertaken in toluene and the product crystallized from toluene/tmeda. Compound 2 presumably arises from one-electron reduction of the 6p-aromatic anion of 1 (Scheme 3). The diamagnetic nature of 2 persists in the solid state and in dilute solutions in toluene as a result of spin-pairing of the electrons within the SbÀSb-bonded dimer, as shown by the structural characterization (see below). This situation contrasts with the behavior of valence-isoelectronic dithiazolyl dimers, for which a dissociation energy of about 0 kJ mol À1 results in extensive dissociation in solution. A few other related 6p-aromatic Group 15 anions have been reported; notably, the coordination chemistry of the 6pbenzatriazolyl ion, [1,2-C 6 H 4 N 3 ] À , which is valence-isoelectronic with the [1,2-C 6 H 4 P 2 Sb] À ion of 1, has been investigated extensively. However, the only representative of this type for the heavier Group 15 elements is the 6p-diaraarzoyl anion [1,2-C 6 H 4 N 2 As] À , which is obtained by the unusual reaction of the lithiate of 1,2-C 6 H 4 (NH 2 ) 2 with (Me 2 N) 2 AsCH 2 As-(NMe 2 ) 2 . To our knowledge, however, one-electron reduction of this type of species has never been detected previously for Group 15 or elsewhere in the p block, except in sulfur/ nitrogen chemistry. The low-temperature solid-state structures of 1 and 2 were both obtained. [9] After many attempts, only one very limited data set was obtained for 1. Although the structural parameters involved should be treated with caution, the nature of the complex has been determined unequivocally, being composed of [Li(tmeda) 2 ] + and 6p-aromatic [1,2-C 6 H 4 P 2 Sb] À ions ). The atoms within each of the four independent C 2 P 2 Sb rings are almost exactly coplanar (maximum deviation 0.020 ), as expected for the conjugation of all of the p orbitals throughout this ring. The small angle at antimony [mean 93.78] is consistent with the lone pair on Scheme 1. Stepwise deprotonation of amines (E = N) and phosphines (E = P). M = As, Sb, Bi, n = 3; Sn n = 2; R = aliphatic or aromatic group.
International Journal of Mass Spectrometry, 2006
The C 6 H 5 C + (OH)OCH 2 • radical cation, formally a distonic isomer of ionized methyl benzoate, has been prepared by dissociative ionization of neopentyl benzoate, as earlier suggested by Audier et al. [H.E. Audier, A. Milliet, G. Sozzi, S. Hammerum, Org. Mass. Spectrom. 25 (1990) 44]. Its distonic character has now been firmly established by its high reactivity towards neutral methyl isocyanide (ionized methylene transfer) producing N-methyl ketenimine ions. Other mass spectrometric experiments and ab initio quantum chemical calculations also concur with each other pointing toward the existence of a stable distonic radical cation.
Dehydrobenzoyl Cations: Distonic Ions with Dual Free Radical and Acylium Ion Reactivity
Journal of the American Chemical Society, 1998
In the gas phase, m-and p-dehydrobenzoyl cations display strong duality of chemical behavior. The ions react selectively as either free radicals or acylium ions, depending on the choice of the neutral reaction partner. Transacetalization with 2-methyl-1,3-dioxolane, ketalization with 2-methoxyethanol, and epoxide ring expansion with epichlorohydrin demonstrate their acylium ion reactivity, whereas • SCH 3 abstraction with dimethyl disulfide demonstrates their free radical reactivity. In one-pot reactions with gaseous mixtures of epichlorohydrin and dimethyl disulfide, the m-and p-dehydrobenzoyl cations react selectively at either site to form the two monoderivatized ions in variable but controlled yields; further reaction at either the remaining radical or the acylium charge site forms a single biderivatized ion as the final product. The o-dehydrobenzoyl cation also displays the expected radical and acylium ion reactivities. But for the ortho isomer, binding of the nucleophilic neutral to the free or derivatized C + dO group facilitates reactions at the radical site. Hence, the ortho isomer displays a unique behavior; its acylium ion reactions either occur simultaneously with, or are followed by, H-abstraction radical reactions. As shown by ab initio calculations, the three isomers display σ-localized odd-spin and π-delocalized charge densities, which characterize distonic structures with molecular orbital-separated radical and charge sites. The dehydrobenzoyl cations are also, according to the calculations, the most stable among 19 of the most feasible C 7 H 4 O +• isomers.