Issue 32, 2023

Variation in pnictogen–oxygen bonding unlocks greatly enhanced Brønsted basicity for the monomeric stibine oxide

Abstract

Phosphine oxides and arsine oxides feature highly polarized pnictoryl groups (Pn+–O/Pn = O; Pn = P, As) and react as Brønsted bases through O-centered lone pairs. We recently reported the first example of a monomeric stibine oxide, Dipp3SbO (Dipp = diisopropylphenyl), allowing periodic trends in pnictoryl bonding to be extended to antimony for the first time. Computational studies suggest that, as the pnictogen atom becomes heavier, delocalization of electron density from the O-centered lone pairs to the Pn–C σ* orbitals is attenuated, destabilizing the lone pairs and increasing the donor capacity of the pnictine oxide. Herein, we assess the Brønsted basicity of a series of monomeric pnictine oxides (Dipp3PnO; Pn = P, As, and Sb). Stoichiometric reactivity between Dipp3PnO and a series of acids demonstrates the greatly enhanced ability of Dipp3SbO to accept protons relative to the lighter congeners, consistent with theoretical isodesmic reaction enthalpies and proton affinities. 1H NMR spectrometric titrations allow for the pKaH,MeCN determination of Dipp3AsO and Dipp3SbO, revealing a 106-fold increase in Brønsted basicity from Dipp3AsO to Dipp3SbO. The increased basicity can be exploited in catalysis; Dipp3SbO exhibits dramatically increased catalytic efficiency in the Brønsted base-catalyzed transesterification between p-nitrophenyl acetate and 2,2,2-trifluoroethanol. Our results unambiguously confirm the drastic increase in Brønsted basicity from Dipp3PO < Dipp3AsO < Dipp3SbO, a direct consequence of the variation in the electronic structure of the pnictoryl bond as the pnictogen atom increases in atomic number.

Graphical abstract: Variation in pnictogen–oxygen bonding unlocks greatly enhanced Brønsted basicity for the monomeric stibine oxide

Supplementary files

Article information

Article type
Paper
Submitted
05 Jul 2023
Accepted
27 Jul 2023
First published
02 Aug 2023

Dalton Trans., 2023,52, 11325-11334

Author version available

Variation in pnictogen–oxygen bonding unlocks greatly enhanced Brønsted basicity for the monomeric stibine oxide

J. S. Wenger, A. Getahun and T. C. Johnstone, Dalton Trans., 2023, 52, 11325 DOI: 10.1039/D3DT02113K

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