Hydride Abstraction and Deprotonation-An Efficient Route to Low Coordinate Phosphorus and Arsenic Species

Abstract

Treatment of Acenap(PiPr2)(EH2) (Acenap = acenaphthene-5,6-diyl; 1a, E = As; 1b, E = P) with Ph3C·BF4 resulted in hydride abstraction to give [Acenap(PiPr2)(EH)][BF4] (2a, E = As; 2b, E = P). These represent the first structurally characterised phosphino/arsino-phosphonium salts with secondary arsine/phosphine groups, as well as the first example of a Lewis base stabilised primary arsenium cation. Compounds 2a and 2b were deprotonated with NaH to afford low coordinate species Acenap(PiPr2)(E) (3a, E = As; 3b, E = P). This provides an alternative and practical synthetic pathway to the phosphanylidene-σ4-phosphorane 3b and provides mechanistic insight into the formation of arsanylidene-σ4-phosphorane 3a, indirectly supporting the hypothesis that the previously reported dehydrogenation of 1a occurs via an ionic mechanism. Hydride abstraction from a primary phosphine/arsine affords the first examples of secondary phosphino/arsino-phosphonium salts. Subsequent deprotonation provides a novel and high yielding route to phosphine-stabilised phosphinidene/arsinidene. These investigations indirectly support an ionic mechanism for the spontaneous dehydrogenation of the primary arsine.