Deoxygenation of chalcogen oxides EO 2 (E = S, Se) with phospha-Wittig reagents.

In here we present the deoxygenation of the chalcogen oxides EO 2 (E = S, Se) with R-P(PMe 3 ), so-called phospha-Wittig reagents. The reaction of DABSO (DABCO·2SO 2 ) with R-P(PMe 3 ) (R = Mes*, 2,4,6- t Bu 3 -C 6 H 2 ; Mes Ter, 2,6-(2,4,6-Me 3 -C 6 H 2 ) 2 -C 6 H 3 ) resulted in the formation of thiadiphosphiranes (RP) 2 S (1:R), while selenadiphosphiranes (RP) 2 Se (2:R) were afforded with SeO 2 , both accompanied by the formation of OPMe 3 . Utilizing the sterically more encumbered Dip Ter-P(PMe 3 ) ( Dip Ter = 2,6-(2,6-iPr 2 -C 6 H 3 ) 2 -C 6 H 3 ) a different selectivity was observed and ( Dip TerP) 2 Se (2:DipTer) along with [Se(μ-P Dip Ter)] 2 (3:DipTer) were isolated as the Se-containing species in the reaction with SeO 2 . Interestingly, the reaction with DABSO (or with equimolar ratios of SeO 2 at elevated temperatures) gave rise to the formation of the OPMe 3 -stabilized dioxophosphorane (phosphinidene dioxide) Dip TerP(O) 2 -OPMe 3 (4:DipTer) as the main product. This contrasting reactivity can be rationalized by two potential pathways in the reaction with EO 2 : (i) a Wittig-type pathway and (ii) a pathway involving oxygenation of the phospha-Wittig reagents and release of SO. Thus, phospha-Wittig reagents are shown to be useful synthetic tools for the metal-free deoxygenation of EO 2 (E = S, Se).