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 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.