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

ABSTRACT: A series of phosphinophosphonium cations ([R₂PPMe₃]⁺; R = Me, Et, ⁱ Pr, ^t Bu, Cy, Ph and N ⁱ Pr₂) have been prepared and examined by collision-induced dissociation (CID) to determine the fragmentation pathways accessible to these prototypical catena-phosphorus cations in the gas-phase. Experimental evidence for fission of P-P and P-E (E = P, C) bonds, and ?-hydride elimination has been obtained. Comparison of appearance potentials for the P-P bond dissociation fragments [R₂P]⁺ (P-P heterolysis) and [PMe₃]⁺? (P-P homolysis) shows that heterolytic P-P cleavage is more sensitive than P-P homolysis towards changes in substitution at the trivalent phosphorus center. The facility of ?-hydride elimination increases with the steric bulk of R in [R₂PPMe₃]⁺. A density functional theory (DFT) study modelling these observed processes in gas-phase, counterion- and solvent-free conditions, to mimic the mass spectrometric environment, was performed for derivatives of [R₂PPMe₃]⁺ (R = Me, Et, ⁱ Pr, ^t Bu, Ph and N ⁱ Pr₂), showing good agreement with experimental trends. The unusual observation of both homolytic and heterolytic cleavage pathways for the P-P and P-C bonds reveals new insight into the fundamental aspects of bonding in monocations and undermines the use of simplistic bonding models.

SUBMITTER: Bamford KL 

PROVIDER: S-EPMC5477047 | biostudies-literature | 2016 Apr

REPOSITORIES: biostudies-literature