Ligand‐Enabled Disproportionation of 1,2‐Diphenylhydrazine at a P^V‐Center**

Abstract

We present herein the synthesis of a nearly square-pyramidal chlorophosphorane supported by the tetradentate bis(amidophenolate) ligand, N,N'-bis(3,5di-tert-butyl-2-phenoxy)-1,2-phenylenediamide.After chloride abstraction the resulting phosphonium cation efficiently promotes the disproportionation of 1,2-diphenylhydrazine to aniline and azobenzene. Mechanistic studies, spectroscopic analyses and theoretical calculations suggest that this unprecedented reactivity mode for P V -centres is induced by the high electrophilicity at the cationic P V -center, which originates from the geometry constraints imposed by the rigid pincer ligand, combined with the ability of the o-amidophenolate moieties to act as electron reservoir. This study illustrates the promising role of cooperativity between redox-active ligands and phosphorus for the design of organocatalysts able to promote redox processes.

Metallomimetic Chemistry of a Cationic, Geometrically Constrained Phosphine in the Catalytic Hydrodefluorination and Amination of Ar–F Bonds

“…The past decade witnessed a growing interest in the chemistry of geometrically constrained main-group centers and their reactivity . A lot of work in this field is focused on the chemistry of geometrically constrained P III centers due to their ability to cycle between two stable oxidation states, P III and P V , which makes them a potent target for metallomimetic chemistry in catalysis .…”

Calix[4]pyrrolato-germane-(thf)2: Unlocking the Anti-van’t Hoff–Le Bel Reactivity of Germanium(IV) by Ligand Dissociation

“…Besides the established strategies to enhance the reactivity of p-block elements by low oxidation or valence states, manipulation of frontier molecular orbital (FMO) energies by structural constraint approaches is gaining recent interest . Accordingly, p-block compounds in non-VSEPR geometries enabled an array of reactivities previously restricted to transition metals or low-valent p-block compounds (refs − ). While most achievements in this area are based on the deformation of group 13 , and 15 ,,, elements (see Figure A for selected examples), only a few structurally constrained group 14 elements have been reported .…”

“…Accordingly, p-block compounds in non-VSEPR geometries enabled an array of reactivities previously restricted to transition metals or low-valent p-block compounds (refs − ). While most achievements in this area are based on the deformation of group 13 , and 15 ,,, elements (see Figure A for selected examples), only a few structurally constrained group 14 elements have been reported . However, based on the predicted changes in frontier molecular orbital energies, the induced effect should be most pronounced upon the planarization of tetrahedral group 14 species .…”

Ligand-enforced geometric constraints and associated reactivity in p-block compounds

“…Alcarazo reported the chlorophosphorane 82 and the corresponding phosphonium cation 83 + -L stabilized by coordination of 4-dimethylaminopyridine (DMAP). 201 Although both of these species are approximately square pyramidal, the proposed free phosphonium cation would feature a ligand-enforced unusual geometry. While the free phosphonium cation was not able to be accessed, it is predicted to have an extremely high Lewis acidity, with a fluoride ion affinity even higher than that of highly fluorinated 84 + .…”

“…Another unique constrained phosphorus compound is the four-coordinate anionic phosphoranide 83 À . [201][202][203] Typical phosphoranide species are 'see-saw' shaped or trigonal bipyramidal if considering the lone pair as a substituent, while the constrained ligand in 83 À forces this molecule into a square pyramidal geometry. 203 Unsurprisingly, reaction with electrophilic methyl iodide gave the five-coordinate phosphorus species 85.…”