The reactivity of diphosphenes towards electrophilic and nucleophilic reagents

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Abstract
The reaction of P2[C(SiMe3)3]2(2) with a stoicheiometric quantity of HCI leads to (Me3Si)3CP(H)–P(Cl)C(SiMe3)3 whilst an excess of this reagent causes PP cleavage and results in the formation of PH(Cl)[C(SiMe3)3]. The corresponding reaction with RPPR (R = 2,4,6-But 3C6H2), (1), results in PH(Cl)R, even when 1 equivalent of HCl is used. Protonation of compound (2) with HBF4·Et2O at –78 °C results in the phosphonium salt [PH3{C(SiMe3)3}][BF4]. Protonation of (1) with HBF4·Et2O is more complex and leads ultimately to PP bond cleavage and insertion of a cationic phosphorus centre into a C–H bond of an ortho-But group. The dication [R(Ag)PP(Ag)R]2+ and the monocation [R(Ag)PPR]+ and [RPP(AuPEt3)R]+ are formed on treatment of (1) with Ag[SO3CF3] or [Au(PEt3)][PF6]. The reaction of (1) with excess of sulphur in the presence of 1,5-diazabicyclo[5.4.0] undec-5-ene results in PP bond cleavage and formation of a cyclic dithiophosphinic acid. The diphosphene, (1), reacts with LiMe to afford the anion [RP–P(Me)R]–. Quenching with MeOH affords the diphosphine R(H)P–P(Me)R, whilst treatment of [RP–P(Me)R]– with OH– causes P–P bond cleavage and formation of the phosphine oxides PH2RO and PH(Me)RO. Treatment of [RP–P(Me)R]– with HBF4·Et2O produces PH2R and the phosphonium salt [PH2(Me)R][BF4]. Treatment of (1) with LiBut also results in anion formation, viz. [RP–P(But)R]–, as the major product which on protonation with MeOH gives the diphosphine R(H)P–P(But)R. The corresponding reaction with LiBun gives the related anion and diphosphine. The reaction of (1) with K[BHBus 3] results only in the diphosphine R(H)P–P(H)R.

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