Carbene‐Stabilized Phosphenium Oxides and Sulfides

Abstract

Carbene→chalcogenophosphenium adducts, which correspond to an intermolecular stabilization mode of the so far elusive, free oxo- and thiooxophosphenium species [R(2)P(+) = X] (X = O, S) by imidazolylidene (NHC) and diaminocyclopropenylidene (BAC) donors, have been isolated and fully characterized. The dative character of the R(2)C:→P(+)(X)Ph(2) bond was confirmed experimentally by nucleophilic displacement of the carbene donor with a chloride ion and by an exchange reaction of the NHC ligand of the NHC:→P(+)(O)Ph(2) adduct with an independently prepared BAC ligand, thereby giving the BAC:→P(+)(O)Ph(2) adduct. This dative character was further characterized by the DFT-calculated preference of carbene→chalcogenophosphenium systems for a heterolytic dissociation mode over a homolytic one.

Recent Advances in Imidazoliumyl‐Substituted Phosphorus Compounds

“…The oxidation of imidazoliumyl‐substituted P III derivatives to the corresponding cationic phosphane sulfide or phosphane oxide succeeds with sulfur or m ‐CPBA ( meta ‐chloroperoxybenzoic acid), respectively …”

Carbeniophosphines versus Phosphoniocarbenes: The Role of the Positive Charge

“…Although the objective of lowering the donating character of the phosphine ligands by incorporating a proximal positive charge has been achieved, carbeniophosphines retain sufficient coordinating ability towards various Lewis acid centers of metallic (Rh I , Pd II , Ni II , Cu I , Ag I , Au I , etc.) and non‐metallic nature (O, S) . Coordinatively inert species were only observed in the case of diimidazoliophosphines, in which the P atom is substituted by two imidazolium moieties.…”

“…and non-metallic nature (O, S). [25,52] Coordinatively inert species were only observed in the case of diimidazoliophosphines, in which the Pa tom is substituted by two imidazolium moieties. For instance, N,N'-(dimethyl)diimidazoliodiphenylphosphine (20;s ee Scheme 6) wasf ound not only to be beyond the coordinating limit towards aR h I center, [34] but also inert with respect to oxidation.…”

The Highly Lewis Acidic Dicationic Phosphonium Salt: [(SIMes)PFPh2][B(C6F5)4]2

“…[16] Compound 5 was combined with Et 3 PO in CD 2 Cl 2 . [13] These data infer that simple coordination of Et 3 PO to the phosphonium P atom of 5 does not occur but rather an oxide-fluoride exchange reaction takes place affording [Et 3 PF][B(C 6 F 5 ) 4 ] (6) and [(SIMes)POPh 2 ][B(C 6 F 5 ) 4 ] (7). This was evidenced by the 31 P NMR spectrum which reveals a doublet resonance at comparably low field (d( 31 P) = 147.2 ppm) with a typical 1 J PF coupling constant of 989 Hz [9] attributed to 6 whereas a singlet resonance observed at 14.0 ppm was attributed to 7.…”

“…This chemical shift is downfield of that observed for the neutral phosphorane (C 6 F 5 ) 3 PF 2 at À48.0 ppm ( 1 J PF = 694 Hz). [13] One of the fluoro-substituents on the cation of 4 is removed upon treatment with Et 3 Si[B(C 6 F 5 ) 4 ]·2 (C 7 H 8 ) giving rise to the dication [(SIMes)PFPh 2 ][B(C 6 F 5 ) 4 ] 2 (5) and the expected by-product Et 3 SiF. The fluoro-substituents occupy the axial positions with a F-P-F angle of 168.8(2)8 while the carbene and the phenyl-substituents occupy equatorial positions.…”