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. 2022 Apr 27;13(20):5957-5963.
doi: 10.1039/d2sc01060g. eCollection 2022 May 25.

Geometrically constrained square pyramidal phosphoranide

Solomon Volodarsky  1 , Irina Malahov  1 , Deependra Bawari  1 , Mohand Diab  1 , Naveen Malik  2 , Boris Tumanskii  1 , Roman Dobrovetsky  1
Affiliations

Geometrically constrained square pyramidal phosphoranide

Solomon Volodarsky et al. Chem Sci. .

Abstract

Geometrical constriction of main group elements leading to a change in the reactivity of these main group centers has recently become an important tool in main group chemistry. A lot of focus on using this modern method is dedicated to group 15 elements and especially to phosphorus. In this work, we present the synthesis, isolation and preliminary reactivity study of the geometrically constrained, square pyramidal (SP) phosphoranide anion (1-). Unlike, trigonal bipyramidal (TBP) phosphoranides that were shown to react as nucleophiles while their redox chemistry was not reported, 1- reacts both as a nucleophile and reductant. The chemical oxidation of 1- leads to a P-P dimer (1-1) that is formed via the dimerization of unstable SP phosphoranyl radical (1˙), an unprecedented decay pathway for phosphoranyl radicals. Reaction of 1- with benzophenone leads via a single electron transfer (SET) to 1-OK and corresponding tetraphenyl epoxide (4).

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1
Fig. 1. Comparison between TBP phosphoranides and 1−.
Scheme 1
Scheme 1. Synthesis of 1-H.
Fig. 2
Fig. 2. POV-ray depiction of 1-H (a), [1−][K(18-crown-6] (b), and the structural features of the SP fragment (c). Thermal ellipsoids at the 50% probability level, non-relevant hydrogens were omitted for clarity.
Scheme 2
Scheme 2. Synthesis of phosphoranide 1−.
Scheme 3
Scheme 3. Preliminary reactivity study of phosphoranide 1−.
Fig. 3
Fig. 3. POV-ray depiction of 1-1 (a) and [1-OK]4 (b). Thermal ellipsoids at the 50% probability level, hydrogens were omitted for clarity.
Fig. 4
Fig. 4. Cyclic voltammetry (CV) of [1−][K(18-crown-6)] (9.3 mM) (a) and 1-1 (3.4 mM) (b) in dry 0.1 M [nBu4N][ClO4]/THF solution obtained at 0.1 V s−1 scan rate using glassy carbon electrodes, Pt wire, and Ag/Ag+ as the working, counter, and reference electrodes, respectively.
Scheme 4
Scheme 4. Generation of 1˙, its dimerization and trap with benzophenone.
Fig. 5
Fig. 5. (a) EPR spectra of 1˙ (blue) and its simulation (red); (b) DFT calculated structure and Mulliken spin densities of 1˙.
Fig. 6
Fig. 6. (a) EPR spectra of [1-OCPh2]˙ under UV-irradiation (λ > 300 nm) at 370 K (blue), and its simulation (red); (b) MS of the reduced [1-OCPh2]˙ (725.3771 (M)−) (red) and its simulation (blue); (c) DFT calculated Mulliken atomic spin densities in [1-OCPh2]˙.
Scheme 5
Scheme 5. Generation of [1-OC(C6F5)2]˙ by two independent routes.
Fig. 7
Fig. 7. (a) EPR spectra of [1-OC(C6F5)2]˙ (blue) and its simulation (red); (b) MS of the reduced [1-OC(C6F5)2]˙ (905.2927 (M)−) (red) and its simulation (blue); (c) DFT calculated Mulliken atomic spin densities in [1-OC(C6F5)2]˙.
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