Electrophile Induced Addition Reactions of Bis-phosphonio-isophosphindolide Cations

Structural and Electronic Properties of Neutral Phosphoniobenzo[c]phospholides

“…[11] In contrast to 2, which binds a Cr(CO) 5 fragment via the endocyclic two-coordinate phosphorus atom, [11] complexation of 3 to a 16e-metal complex fragment is expected to occur at the exocyclic phosphane moiety, as in the anion 4. [8] More importantly, the π-bond localisation in neutral phosphoniobenzophospholides towards a phosphaalkeneϪ benzylidene ylide electronic structure, suggests that these compounds should also display an increased susceptibility towards addition [such as addition of reactive EϪH bonds which have been found to occur for less reactive bis(phosphonio)-substituted cations [5] ], or even cycloaddition reactions at the PϪC double bond, or Wittig reactions at the ylide moiety. Investigations aiming at the verification of these reaction schemes for 2, where the largest degree of π-bond localisation is observed, are currently in progress.…”

“…[2,3] Although electron delocalisation over the phosphonio groups and the π-electron system is low, [2,4] the electrostatic influence of the substituents still induces a marked reduction in nucleophilicity relative to the anionic phospholide derivatives, and polarises the π-electron distribution in the ring. [2Ϫ4] As a consequence of these effects, bis(phosphonio)benzophospholides display a very balanced nucleophilic and electrophilic reactivity, which is the primary reason for their remarkable stability towards solvolysis and addition reactions, [1,3,5] and their preference to coordinate to transition metal atoms through the phosphorus lone-pair [3,6] rather than the π-electron system as most other phospholide-type ligands. [7] In the course of the investigation of the chemical properties of bis(phosphonio)benzophospholides, we established that reduction of 1 gives easy access to both neutral, zwitterionic phosphoniobenzophospholides 2, 3, and phosphanylbenzophospholide anions 4 (see Scheme 1).…”

The Continuing Development of the Chemistry of Phospholes

“…The phosphino group in 188 exhibited typical properties and was converted to the borane adduct 189 and to the sulfide 190. Protonation, however, occurred on the carbon atom [81] giving a species that was very susceptible to addition of water or methanol.…”

Anellated Heterophospholes and Phospholides and Analogies with Related Non-Phosphorus Systems

“…Bis(phosphonio)isophosphindolides, which display a related but symmetric π-excessive aromatic system with charge compensation by substituents, lack this high sensitivity to water or alcohol . However, electron withdrawal from phosphorus by coordination to transition metal cations or by oxidation enhances the reactivity and promotes rapid reaction with H 2 O, alcohols, or H 2 S. 102c,,− In 1,3-benzazaphospholes and 1-phosphaindolizines, the +M effect of the nitrogen electron-pair reduces the polarity of the CP bond and makes these compounds more resistant to hydrolysis. Analogously, 1,3-benzoxaphospholes are stabilized by the +M effect of the O-atom.…”

“…Equimolar amounts of TfOH lead to an equilibrium with two species, in which one or both carbon atoms adjacent to phosphorus are protonated. Addition of small amounts of water to the acidic THF solution causes rapid hydrolysis yielding the acyclic bis(phosphonium) salt via a cyclic phosphinoxide and a phosphonous acid intermediate detected by NMR . The hydrolytic sensitivity of 55a (X = I 3 ) is markedly increased by the mildly oxidizing counterion giving rise to a cyclic phosphinic acid derivative if the solution is exposed to moist air.…”