Azidophosphenium Cations: Versatile Reagents in Inorganic Synthesis

Abstract

This work describes the synthesis and characterization of a series of iminophosphorane-substituted phosphenium cations of the type [R2NPNP(Cl)2NPNR'2][GaCl4] [R = iPr; R' = iPr (7[GaCl4]), SiMe3 (8)], which are directly derived from azidophosphenium salt [iPrNPN3][GaCl4] (2iPr[GaCl4]) and the corresponding chlorophosphane R2NPCl2. The reactivity of 7[GaCl4] toward 2,3-dimethylbutadiene (dmb) and 2,2'-bipyridine (bipy) was investigated, resulting in the formation of 7-dmb[GaCl4] and 7-Cl. In addition, self-condensation of [(Me3Si)2NPN3][GaCl4] (2SiMe3[GaCl4]) was studied in detail, and [(Me3Si)2NPNP(XY)N(SiMe3)2][GaCl4] [X = Cl; Y = Cl (13), N3 (14)] were determined as products on the basis of (31)P NMR spectroscopy. The reaction of 2SiMe3[GaCl4] with [(Me3Si)2NPCl][GaCl4] (1SiMe3[GaCl4]) yielded an unprecedented bicyclic 1,3,2λ(3),4λ(5)-diazadiphosphetidine (15), which was formed via a GaCl3-assisted Me3SiCl elimination starting from 13. Furthermore, cations of the type [R2NPNPR'3][GaCl4] [R = iPr; R' = cHex (19)] were obtained by the effective combination of 2R[GaCl4] (R = iPr, SiMe3) with PR'3 (R' = Ph, cHex). Azidochlorophosphanes R2NP(N3)Cl [R = iPr, SiMe3 (20R)] are shown to be accessible when 2R[GaCl4] was combined with bipy. All new compounds were fully characterized by means of X-ray, vibrational spectroscopy, CHN analysis, and NMR experiments. All compounds were further investigated by means of density functional theory, and the bonding situation was accessed by natural bond orbital analysis.

A Ferrocenophane-Based Diaminophosphenium Ion

“…The observation of intermolecular contacts at directions that are often close to perpendicular to the local NPN plane is a common phenomenon in crystal structures of phosphenium ions and is attributable to electrostatic stabilization of the highly electrophilic cations. ,, However, intermolecular P···Cl interactions in diaminophosphenium tetrachloroaluminates and -gallates remain close to the sum of van der Waals radii (P–Cl > 3.4 Å), whereas short contacts with similar distances as in 2a [AlCl 4 ] are only known for strongly electrophilic cations obtained by formal exchange of one amino group by a substituent of weaker π-donating power. ,, In this context, we regard both the short interion contacts in crystalline 2a [AlCl 4 ] and the observation of a relatively short P–Cl distance in the chlorophosphine precursor 1a as structural indicators of an unusually high (for a cyclic diaminophosphenium ion) Lewis acidity of 2a + . Enhanced electrophilicity with respect to conventional N-heterocyclic derivatives was also observed for ferrocenophane-based carbenes and is presumably attributable to the increased bond angle enforced by the geometrical constraints of the ferrocenophane skeleton. , It should be noted, however, that the electron-withdrawing power of the cation causes hardly any imbalance between the distances of ’”coordinating” (2.123(2), 2.130(2) Å) and “free” (2.131(2), 2.134(2) Å) Al–Cl bonds, all of which remain essentially indistinguishable within experimental error …”

On New Staudinger Type Reactions of Phosphorus Centered Biradicaloids, [P(μ‐NR)]2 (R = Ter, Hyp), with Ionic and Covalent Azides

“…As depicted in Scheme 7, reaction of 1 Hyp with Mes*‐N 3 resulted in a completely different reaction channel leading to the formation of a cyclo‐diazaphosphetidine 4 HypMes*_ P6 (Figure 4 top, Scheme 8 corresponds to isomer P6 ) without release of molecular nitrogen. [ 71,72,81,82,73–80 ] The 31 P NMR spectrum featured two doublet resonances at 9.9 ppm for the four‐coordinate and 382.5 ppm ( 2 J [ 31 P‐ 31 P] = 39 Hz) for the two‐coordinate phosphorus atoms. With a decomposition point of 91 °C, 4 HypMes*_ P6 is thermally less stable compared to the pentadienes ( 3 HypDipp_ I2 : 122°, 3 HypTer_ I5 : 231 °C).…”

Kinetically Stabilized Diarylpnictogenium Ions

“…[95] Crystallographic data for the structural analyses have been deposited with the Cambridge Crystallographic Data Centre, Nos. 2220584 (7) and 2220585 (8). Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: + 44-1223-336033; e-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).…”

“…Unlike those, pnictogenium ions are also strong electrophiles, which can be attributed to the positive charge that attracts any nucleophile present. Consequently, the vast majority of phosphenium ions, [R 2 P] + , [2–33] arsenium ions, [R 2 As] + , [34–51] stibenium ions, [R 2 Sb] +[52–59] and bismuthenium ions, [R 2 Bi] + , [60–72] reported in the literature are either affected by ion pairing or stabilized by electron‐rich ligands or substituents, which inter‐ or intramolecularly fill the vacant p‐orbital. These electronically stabilized pnictogenium ions often have a dramatically reduced Lewis acidity and cannot be regarded as genuine 6 VE species as they fulfill or even exceed the octet rule.…”