Stable Open-Shell Phosphorane Based on a Redox-Active Amidodiphenoxide Scaffold

Abstract

The synthesis and redox reactivity of pentacoordinate phosphorus compounds incorporating a redox-active ONO amidodiphenoxide scaffold [ONO = N,N-bis(3,5-di-tert-butyl-2-phenoxide)amide] are described. Dichloro- and diphenylphosphoranes, 2·Cl and 2·Ph, respectively, are synthesized and crystallographically characterized. Cyclic voltammograms of 2·Cl show only a single irreversible oxidation (E = +0.83 V vs CpFe), while the diphenyl analogue 2·Ph is reversibly oxidized at lower applied potential (E = +0.47 V vs CpFe). Chemical oxidation of 2·Ph with AgBF produces the corresponding radical cation [2·Ph], where electron paramagnetic resonance spectroscopy and density functional theory calculations reveal that the unpaired spin density is largely ligand-based and is highly delocalized throughout the ONO framework of the paramagnetic species. The solid-state structures indicate only minor geometrical changes between the neutral 2·Ph and oxidized [2·Ph] species, consistent with fast self-exchange electron transfer, as observed by NMR line-broadening experiments.

On the Redox Reactivity of a Geometrically Constrained Phosphorus(III) Compound

“…The synthesis of the analogous difluoride compound, P(ONO)F 2 ,h as also been investigated, using xenon difluoride as as ource of F 2 .W hen this reaction is performed in deuterated dichloromethane the solution turns black immediatelya nd 31 PNMR spectroscopy reveals a2 :1 product mixture,w ith a doublet of doublets resonance centred at À31.9 ppm and a triplet resonancec entred at À38.1 ppm, respectively.T he former collapses to ad oublet upon proton decoupling.C om-plementary 1 J FÀP coupling constants are observed in the 19 FNMR spectrum ( 1 J FÀP = 872 and 1047 Hz, respectively). The NMR spectral data suggests the formation of both the targeted phosphorus difluoride (the species observed at À38.1 ppm) and also the hydrofluoride, P(ONO)(H)F (5), which is formed as the major product.…”

“…All of these reactions generated the dihalide compounds P(ONO)X 2 where X=Cl ( 2 ), Br ( 3 ) and I ( 4 ). It should be noted that 2 was first reported by Contreras and co‐workers and was recently employed by Radosevich for the synthesis of phosphorane based radicals . Upon dissolving the two reagents in toluene full consumption of 1 was observed by 31 P NMR spectroscopy and the formation of the respective phosphorus(V) dihalides was indicated by singlet resonances at −21.0 ( 2 ), −88.2 ( 3 ) and −258.3 ppm ( 4 ).…”

“…It should be noted that 2 was first reported by Contreras and co-workers and was recently employed by Radosevich for the synthesis of phosphoraneb ased radicals. [18,19] Upon dissolving the two reagents in toluenef ull consumption of 1 was observed by 31 PNMR spectroscopy and the formation of the respective phosphorus(V) dihalides was indicated by singlet resonances at À21.0 (2), À88.2 (3)a nd À258.3 ppm (4). The NMR data for 2 and 3 are in good agreement with other related phosphorus(V) dihalides previously reported by Arduengo.…”

“…Selectedb ond lengths[ ]and angles [8]: 2:P1 ÀN1 1.696(1), P1ÀO1 1.667(1), P1ÀO2 1.667(1), P1ÀCl12.038(1), P1À Cl2 2.047(1); O1-P1-O2 167.91 (5), O1-P1-N188.86(4), O1-P1-Cl1 95.71(4), O1-P1-Cl2 87.52 (3), O2-P1-N18 8.71(4), O2-P1-Cl1 96.21(4), O2-P1-Cl2 87.49(4), N1-P1-Cl1 111.11 (4), N1-P1-Cl2 143.98(4), Cl1-P1-Cl2 104.91 (2). 3:P 1-N1 1.702(4), P1-O1 1.661(3), P1-O21 .663(3), P1-Br1 2.219(2), P1-Br 2.235(2);O 1-P1-O2 165.42 (19), O1-P1-N188.51 (17), O1-P1-Br1 96.98 (13), O1-P1-Br2 86.40 (12),O 2-P1-N18 9.94 (18), O2-P1-Br1 97. 29(14), O2-P1-Br2 86.82 (12),N1-P1-Br1 107.88 (15), N1-P1-Br2 146.11(16), Br1-P1-Br2 105.99 (5).…”

Sterically Constrained Bicyclic Phosphines: A Class of Fascinating Compounds Suitable for Application in Small Molecule Activation and Coordination Chemistry

“…These dihalides allow the synthesis of cationic species, in part by treatment with strong Lewis acids as anion receptors. A relatively persistent radical cation has been obtained by oxidation of a diphenyl derivative derived from 2 , whereas the corresponding dichloride 13 b showed only an irreversible oxidation. Reduction of the phosphine 2 with strongly reducing KC 8 resulted in P−P bond formation .…”