Cationic Phosphinidene as a Versatile P 1 Building Block: [L C -P] + Transfer from Phosphonio-Phosphanides [L C -P-PR 3 ] + and Subsequent L C Replacement Reactions (L C = N-Heterocyclic Carbene).

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