Meisenheimer Complexes Positively Characterized as Stable Intermediates in the Gas Phase

Abstract

Prototypical Meisenheimer complexes are characterized as stable, covalent intermediates in the gas phase, using a novel, highly diagnostic spectroscopic technique that exploits the potential emerging from the combination of mass spectrometry with an IR FEL radiation source

Di‐ and Trifluorobenzenes in Reactions with Me2EM (E = P, N; M = SiMe3, SnMe3, Li) Reagents: Evidence for a Concerted Mechanism of Aromatic Nucleophilic Substitution

“…[12][13][14] This conclusion is supported by the observation of Meisenheimer complexes formed by nitroarenes in the gas phase. [15] It is of fundamental importance that neither high basicity of an entering or leaving ligand nor efficient resonance stabilization of a negative π-charge in a ring are present in the compounds of our study. These properties are unfavourable for the S N Ar mechanism, thus strongly supporting the A N D N mechanism.…”

Nitrosyl–heme and anion–arene complexes: structure, reactivity and spectroscopy

“…Thus, IRMPD spectroscopy has provided for the first time conclusive evidence for the existence of Meisenheimer complexes in the gas phase (see Fig. 2 with X = H and Y = OH, OCH 3 , OC 2 H 5 ) [23,24].…”

“…In our work we have examined the binding features of a prototypical electron-deficient aromatic system [1,3,5-trinitrobenzene (TNB)] with exemplary anions (OH -, OCH 3 -, OC 2 H 5 -, F -, Cl -, Br -, I -, CN -) in the gas phase using the combined information deriving from collision induced dissociation experiments at variable energy, IRMPD spectroscopy and quantum chemical calculations. The first spectroscopic evidence about the existence of a covalently bound anionic σ-complex in the gas phase has been obtained by delivering TNB-CH 3 O -ions into the gas phase by ESI of a basic methanol solution of TNB [24]. The so-formed ions have been assayed in the 900-1700 cm -1 range where prominent signatures associated to the symmetric stretching vibrations of the nitro groups are expected.…”

“…The first complex isolated by Meisenheimer in 1902 and characterized by the crystal structure responds to X = Y = OCH 3 . A relatively novel, structurally diagnostic tool has recently allowed us to ascertain the bonding features of the gaseous adducts of simple anions (OH -, OCH 3 -, OC 2 H 5 -, F -, Cl -, Br -, I -, CN -) with a π-acidic arene (1,3,5-trinitrobenzene, TNB) [21][22][23][24].…”

Communication: Vibrational study of a benzyl carbanion: Deprotonated 2,4-dinitrotoluene

“…6,7 Recently, the structural characteristics of complexes formed in solution by the addition of anions (alkoxides, hydroxide, halides) to 1,3,5-trinitrobenzene (TNB) have been elucidated in the gas phase by infrared multiple photon dissociation (IRMPD) spectroscopy in the highly informative fingerprint region. 8,9 The fruitful combination of vibrational spectroscopy, mass spectrometry, and quantum chemical calculations has allowed us to unveil that the sampled electrosprayed adducts conform to different binding motifs, depending on the nature of the anion: (i) a strongly covalent σ -adduct (Meisenheimer complex), with a tetrahedral carbon center, in the case of [TNB-OH] − and [TNB-OCH 3 ] − complexes; (ii) a donor-π -acceptor complex (also assigned the characteristics of a weak σ interaction), displaying a relatively unperturbed TNB unit, in the case of [TNB-Br] − and [TNB-I] − complexes. However, the formation of anionic a) Author to whom correspondence should be addressed.…”