Cyclotetraphosphinophosphonium Ions:  Synthesis, Structures, and Pseudorotation

Abstract

The first derivatives of catenated cyclotetraphosphinophosphonium cations, [(PhP)4PPhMe]+ (8a), [(MeP)4PMe2]+ (8b), [(CyP)4PPh2]+ (8d), [(CyP)4PMe2]+ (8e), [(PhP)4PPh2]+ (8f), [(PhP)4PMe2]+ (8g), are synthesized as trifluoromethanesulfonate (triflate, OSO2CF3-) salts through the reaction of cyclopentaphosphines (PhP)5 (4a) or (MeP)5 (4b) with methyl triflate (MeOTf) or by a net phosphenium ion [PR2+, R = Ph, Me; from R2PCl and trimethylsilyltriflate (Me3SiOTf)] insertion into the P-P bond of either cyclotetraphosphine (CyP)4 (3c) or cyclopentaphosphines (PhP)5 (4a) or (MeP)5 (4b). Although more conveniently prepared from 4a, compound 8a[OTf] can also be formed from (PhP)4 (3a) and MeOTf, and derivatives 8f[OTf] and 8g[OTf] are also accessible through reactions of 3a and R2PCl/Me3SiOTf with R = Ph or Me, respectively. A tetrachlorogallate salt of [(PhP)4PPhtBu]+ (8c) has been synthesized by alkylation of 4a with tBuCl/GaCl3. 31P[1H] NMR parameters for all derivatives of 8 have been determined by iterative simulation of experimental data. Derivatives 8a[OTf], 8b[OTf], 8c[GaCl4], 8e[OTf], 8f[OTf], and 8g[OTf] and have been characterized by X-ray crystallography, showing the most favorable all-trans configuration of substituents for the phosphine centers, thus minimizing steric interactions. Each derivative adopts a unique envelope or twist conformation of C1 symmetry. The effective C2 symmetry observed for 8b, d, e, f, and g in solution, signified by their 31P[1H] NMR AA'BB'X spin systems, implies a rapid conformational exchange for derivatives of 8. The core frameworks of the cations in the solid state are viewed as snapshots of different conformational isomers within the solution-phase pseudorotation process.

P−P Condensation and P−N/P−P Bond Metathesis: Facile Synthesis of Cationic Tri‐ and Tetraphosphanes

“…Research Articles 3586 www.angewandte.org by diffusion of Et 2 Oi nto aC H 3 CN solution of 4b[OTf] at À30 8 8C. [21] Them olecular structures are shown in the Supporting Information, Figure S2 for 4a[OTf] and in Figure 1 for 4b [OTf].S imilar to related 1,2,3-triphospholane derivatives, [16,23] both cations show an envelope conformation of the five-membered ring in the solid state in which the phenyl and the imidazoliumyl substituents adopt an all-trans configuration. TheP ÀPb ond lengths range from 2.2156(4) to 2.2291-(4) and are comparable to other structurally related 1,2,3triphospholanes.…”

catena‐Phosphorus Cations

“…Triphosphinophosphonium ( D ) and tetraphosphinophosphonium ( E ) cations were first proposed on the basis of elemental analysis data for compounds isolated from the alkylation of cyclotetra‐ and cyclopentaphosphines with CCl 4 or MeI,40–42 but examples have only recently been definitively characterized 39. 43–46 Triflate salts of cations with frameworks C‐1 ,44 D ‐1 ,44 and E‐1 45 can be prepared in high yields by methylation or protonation ( D ‐1 only) of cyclopolyphosphines (Scheme ). Frameworks D ‐2 and E‐2 are also formed by insertion of a phosphenium ion into cyclotri‐ and tetraphosphines to give ring‐expanded cations (Scheme ).…”

Lewis Base Stabilized Oxophosphonium Ions

“…[7,8] The area has seen a recent resurgence [6,[9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] which may be due to the popularity of the isovalent singlet carbenes and, as such, the use of phosphenium ions as ligands in transition metal chemistry has been exploited. [24][25][26][27][28][29][30] In the context of main group chemistry, [31] phosphenium ions have been involved in the preparation of phosphinophosphonium systems, [32][33][34][35][36][37][38][39][40] as well in reactions with P 4 , [39,[41][42][43][44] and other reagents. [15] Approximately 20 years ago, the synthesis of terminal thioxo-and selenoxophosphonium ions were targeted by Burford et al, [45][46][47] however these attempts resulted in the formation of dimeric structures B.…”