Peri-substituted phosphino-phosphonium salts: synthesis and reactivity

The clean reaction of 5-lithio-6-(diisopropylphosphino)acenaphthene with dichlorophosphines RPCl2 gives the peri-substituted phosphino-phosphonium salts [Acenap(PiPr(2))(PR)]Cl-+(-) (2, R = Ph; 3, R = Fc; 4, R = NMe2; 5, R = iPr; Acenap = acenaphthene-5,6-diyl). Their ionic structure is maintained in solution and in the solid state. The reduction of 2 and 3 with LiAlH4 led to the formation of mixed tertiary/secondary chelating bis(phosphines) Acenap(PiPr(2))(PRH) (6 and 7), which were subsequently reacted with PtCl2(cod) to give the complexes [(6)/(7)PtCl2] (8 and 9). Reaction of 2 and 3 with a large excess of MeOTf at elevated temperature gave the chiral 1,2-diphosphoniums [Acenap(PiPr(2))(PRMe)](2+)([TfO](-))(2) (10 and 11), which were reduced with LiAlH4 to the heteroleptic bis(phosphines) Acenap(PiPr(2))(PRMe) (12 and 13); these were then reacted with [(nor)Mo(CO)(4)] to give the complexes [(12)/(13)Mo(CO)(4)] (14 and 15). The heteroleptic bis(phosphines) 6, 7, 12, and 13 display large through-space couplings (formally (4)J(PP) = 163-199 Hz), comparable in magnitude to (1)J(PP) couplings observed in phosphino-phosphonium salts 2-5 (303-412 Hz). Single-crystal X-ray structures of 2, 3, 7-9, 14, and 15 are reported.