Cationic Phosphorus Compounds Based on a Bis(1-piperidinyl)-Substituted Carbodiphosphorane: Syntheses, Structures, and C_sp³ -H Activation.

ABSTRACT: The use of the bis(1-piperidinyl)-substituted carbodiphosphorane (Ph₂(Pip)P)₂C (1) as an NCN ligand for the stabilization of phosphorus cations was studied. A simple ligand for halide exchange allowed the synthesis and isolation of a series of phosphorus monocations of the type [1-PR₂]⁺ (with R = Cl, Br, I, CyCl, Ph). These cations exhibit characteristic NMR and structural properties which nicely correlate with the charge at the central phosphorus atom and the interaction between the ligand and the PR₂ moiety. Halide abstraction from the monocations does not result in isolable dicationic compounds but in an unexpected intramolecular C_sp³ -H activation in the piperidinyl group. DFT studies show that the selective activation of the CH₂ group next to the nitrogen atom instead of a CH group at the phenyl substituents proceeds via an iminium intermediate formed by hydride transfer from the carbon atom to the cationic phosphorus center. This observation clearly demonstrates the pronounced ? acidity of the dicationic phosphorus species in comparison to compounds with a further ?-donor substituent.

SUBMITTER: Kroll A 

PROVIDER: S-EPMC7861138 | biostudies-literature | 2020 Dec

REPOSITORIES: biostudies-literature