Atom Swapping on Aromatic Rings: Conversion from Phosphinine Pincer Metal Complexes to Metallabenzenes Triggered by O₂ Oxidation

Abstract

Herein, we report a novel method for the synthesis of metallabenzenes by swapping the phosphorus atom in an aromatic phosphinine ring with transition metal fragments. The oxidation of a phosphine‐phosphinine‐phosphine pincer iridium complex by O2 triggered the replacement of the phosphorus atom of the phosphinine ring by an iridium fragment to afford iridabenzene. Dianionic rhodabenzene was also synthesized from a phosphinine rhodium complex by oxidation of the phosphorus atom, followed by subsequent reduction using metallic potassium. The aromaticity of the newly synthesized irida‐ and rhoda‐benzenes was evaluated both experimentally and theoretically.

Structure and Reactivity of Ag(I) Complexes Bearing Tridentate Phosphinine Ligands

“…First, λ 3phosphinine complex 2 was synthesized. A phosphine− phosphinine−phosphine pincer ligand 1 was synthesized following to a procedure slightly modified from our previous report for a PCy 2 analogue 34 (see the Supporting Information for detail). Ligand 1 was then treated with an equimolar amount of AgBF 4 to afford a dimeric silver complex 2 in a quantitative yield (Scheme 3).…”

“…We recently reported a novel phosphine−phosphinine− phosphine pincer ligand (Scheme 1c). 34 The O 2 oxidation of the Rh(I) complex produced a λ 5 -phosphinine complex, in which the phosphinine ring coordinates to Rh(I) in an η 5fashion. The subsequent reduction by metallic potassium resulted in the formation of rhodabenzene, which was the first synthesis of rhodabenzene.…”

“…In this case, the phosphinine moiety was oxidized by a diazoacetate or hexachloroethane without dimerization, but the ligand dissociated from the metal center. We recently reported a novel phosphine–phosphinine–phosphine pincer ligand (Scheme c) . The O 2 oxidation of the Rh­(I) complex produced a λ 5 -phosphinine complex, in which the phosphinine ring coordinates to Rh­(I) in an η 5 -fashion.…”

Efficient iron-catalyzed direct acylation of amines with carboxylic acids and esters under oxygenated conditions

“…In addition, activation by dioxygen has resulted to be essential for certain challenging reactions such as skeletal rearrangements 24 photoisomerization between the cis and the trans states of azobenzenes 25 and other oxygen-driven photoisomerization reactions of alkenes and polyenes, 26 redox-neutral nucleophilic aromatic substitutions leading to seven-membered ring formation, 27 conversion of pincer metal complexes into metallabenzenes, 28 and iron-catalyzed dearomatization of 2-naphthols. 29…”

Diphosphene with a phosphineborane tether and its rhodium complex

“…This situation sharply contrasts the abundance of multidentate ligands in phosphaalkenes and phosphinines in combination with oxazoline, pyridine, phosphine, etc. 16,17 In this regard, we planned to synthesize diphosphene 1′ with a PP bond and a phosphine (Fig. 1c).…”