Abstract
Cationic imidazoliumyl(phosphonio)-phosphanides [L(C)-P-PR(3)](+) (1a-e(+), L(C) = 4,5-dimethyl-1,3-diisopropylimidazolium-2-yl; R = alkyl, aryl) are obtained via the nucleophilic fragmentation of tetracationic tetraphosphetane [(L(C)-P)(4)][OTf](4) (2[OTf](4)) with tertiary phosphanes. They act as [L(C)-P](+) transfer reagents in phospha-Wittig-type reactions, when converted with various thiocarbonyls, giving unprecedented cationic phosphaalkenes [L(C)-P═CR(2)](+) (5a-f[OTf]) or phosphanides [L(C)-P-CR(NR(2)('))](+) (6a-d[OTf]). Theoretical calculations suggest that three-membered cyclic thiophosphiranes are crucial intermediates of this reaction. To test this hypothesis, treatment of [L(C)-P-PPh(3)](+) with phosphaalkenes, that are isolobal to thioketones, permits the isolation of diphosphirane salts 11a,b[OTf]. Furthermore, preliminary studies suggest that the cationic phosphaalkene [L(C)-P═CPh(2)](+) may be employed to access rare examples of η(2)-P═C π-complexes with Pd(0) and Pt(0) when treated with [Pd(PPh(3))(4)] and [Pt(PPh(3))(3)] for which analogous complexes of neutral phosphaalkenes are scarce. The versatility of [L(C)-P](+) as a valuable P(1) building block was showcased in substitution reactions of the transferred L(C)-substituent using nucleophiles. This is demonstrated through the reactions of 5a[OTf] and 6c[OTf] with Grignard reagents and KNPh(2), providing a convenient, high-yielding access to MesP═CPh(2) (16) and otherwise difficult-to-synthesize 1,3-diphosphetane 17 and P-aminophosphaalkenes.