Bond fission in monocationic frameworks: diverse fragmentation pathways for phosphinophosphonium cations

Abstract

Bond dissociation pathways for phosphinophosphonium cations have been addressed through the concerted application of ESI-CID-MS/MS and DFT modelling.

Using the Lewis Acid Me3Si−F−Al(ORF)3 To Prepare Phosphino‐Phosphonium Cations with the Least‐Coordinating Anion [(RFO)3Al−F−Al(ORF)3]−

“…For the [R 2 P−PMe 3 ] + cations, the differences between Δ G (hetero) and Δ G (homo) in the gas phase are only +41 kJ mol −1 (R=Me) and −69 kJ mol −1 (R=Ph). The calculated values are in agreement with Burford's findings that homolytic P−P bond cleavage is preferred in [Me 2 P−PMe 3 ] + , whereas for [Ph 2 P−PMe 3 ] + only heterolytic bond cleavage is observed . However, when looking at the calculated data in polar solvents, the energy difference between homolytic and heterolytic bond cleavage becomes considerably smaller.…”

“…Yet, this non‐bonded structure as well as the dative version would speak for a weak P−P bond. To shed some light on this riddle, Burford recently published both a computational and a very extensive experimental study on the bonding of the [R 2 P−PMe 3 ] + cations in the gas phase, leading to the legitimate conclusion that the positive charge in these cations is significantly delocalized over the entire system and cannot be described by the sole use of dative or Lewis representations as shown in Scheme , top row. From this study emerged that the P−P bonds in this system are rather strong!…”

“…Given that the homolytic P−P bond cleavage was shown to be predominant in the gas phase for [Me 2 P−PMe 3 ] + to yield [Me 2 P] . and [PMe 3 ] .+ , we were interested in whether a highly polar environment has an influence on the dissociation energy of the P−P bond in these cations. They might favor the [R 2 P] + cation over the [R 2 P−PMe 3 ] + cation because it is considerably smaller and therefore, Δ solv G 0 should be higher.…”

“…Note, however, the dispute on the coordinate description . Recently Burford and co‐workers performed extensive studies on the nature of the P−P bond in these cations and concluded that the positive charge is completely delocalized, which is neither well‐described by Lewis nor coordinate notation, but only by a combination of both …”

Ferrocene‐Based Phosphenium Ion with Intramolecular Phosphine Coordination

“…In addition, we expected the Fc P group would afford the reversible donor coordination due to the rotation of the cyclopentadienyl moiety, which could control the stability of the phosphenium ion, i. e., 1 + could exhibit both stability and reactivity because of the interconversion between the stable phosphine-coordinated phosphonium form 1A + and the reactive "free" phosphenium form 1B + (Figure 1). [12] On the other hand, the sterically demanding ferrocenyl group, Fc*, should afford kinetic stability to the phosphenium ion, expecting the stability for handling in the air. Here, we report the synthesis of phosphenium ion…”