title: Diverse reactivity of the cyclo-diphosphinophosphonium cation [(PtBu)₃Me]⁺: parallels with epoxides and new catena-phosphorus frameworks.
abstract: The cyclo-diphosphinophosphonium salt [(PtBu)3Me][OTf] (2) has been shown to be highly reactive toward Lewis bases, exhibiting diverse reactivity with phosphines, 4-(dimethylamino)pyridine (dmap) and chlorophosphines, providing approaches to new open-chain and cyclic catena-phosphorus frameworks. Reaction of 2 with R3P (R = Me or nPr) or dmap led to the ring-opened adducts [R3P-PtBu-PtBu-P(Me)tBu][OTf] (R = Me (4a), nPr (4b)) and [(dmap)-PtBu-PtBu-P(Me)tBu][OTf] (6), respectively. The complicated (31)P{(1)H} NMR spectra of the three compounds were simulated, evidencing the presence of two diastereomeric forms of 4a, and single diastereomers of 4b and 6. This ring-opening reactivity of the cation in 2 parallels the reactivity of isolobal epoxides with nucleophiles under acidic conditions. Compound 2 was also shown to react with a 2:1 mixture of Me2PCl and TMSOTf to form the unexpected cyclo-diphosphino-1,2-diphosphonium salt [(Me2P)2(PtBu)2][OTf]2 (8), which is postulated to result from two consecutive ring-opening and ring-closing steps. In contrast, reaction with MePCl2 furnished [(MeP)(PtBu)2(P(Me)tBu)][OTf] (9), consistent with insertion of a "MeP" moiety into the cationic phosphorus framework of 2. The importance of ring strain on the reactivity of the cation in 2 was illustrated by comparative studies of the corresponding cyclo-tetraphosphorus cation in [(PtBu)4Me][OTf] (10), which exhibits no reactivity under analogous conditions.
authors.affiliation: Department of Chemistry, University of Victoria , Victoria, British Columbia V8W 3V6, Canada.
authors.forename: Alasdair P M
authors.initials: AP
authors.lastname: Robertson
authors.forename: C Adam
authors.initials: CA
authors.lastname: Dyker
authors.forename: Paul A
authors.initials: PA
authors.lastname: Gray
authors.forename: Brian O
authors.initials: BO
authors.lastname: Patrick
authors.forename: Andreas
authors.initials: A
authors.lastname: Decken
authors.forename: Neil
authors.initials: N
authors.lastname: Burford