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(PiPr2)­(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(PiPr2)­(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(PiPr2)­(PRMe)]2+([TfO]−)2 (10 and 11), which were reduced with LiAlH4 to the heteroleptic bis­(phosphines) Acenap­(PiPr2)­(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 4JPP = 163–199 Hz), comparable in magnitude to 1JPP 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.