Functionalization of Intact Trimetaphosphate: A Triphosphorylating Reagent for C, N, and O Nucleophiles

Trimetaphosphate (TriMP, [P3O9]3–) reacts with PyAOP ([(H8C4N)3PON4C5H3]­[PF6]) to yield an activated TriMP, [P3O9P­(NC4H8)3]− (1), incorporating a phosphonium moiety. Anion 1 is isolated as its bis­(triphenylphosphine)­iminium (PPN) salt in 70% yield and phosphorylates nucleophiles with elimination of phosphoramide OP­(NC4H8)3. Treatment of 1 with amines HNR1R2 generates [P3O8NR1R2]2– (2a: R1 = R2 = Et; 2b: R1 = H, R2 = tBu) in greater than 70% yield as mixed PPN and alkyl ammonium salts. Treatment of 1 with primary alcohols in the presence of a tertiary amine base results in salts of intact TriMP alkyl esters [P3O9R]2– (3a: R = Me; 3b: R = Et) in greater than 60% isolated yield. Reaction of 1 with [PPN]­[H2PO4] provides orthophosphoryl TriMP (4, [P4O12H2]2–) in 40% yield as the PPN salt. Treatment of 1 with Wittig reagent H2CPPh3 (4 equiv) provides phosphorus ylide [P3O8CHPPh3]2– (5) in 61% yield as a mixed salt. Ylide 5 reacts with water to provide [P3O8Me]2– (6) and with aldehydes to give olefins [P3O8CHCHR]2– (7a: R = H; 7b: R = 4-C6H4Br), products in which one TriMP oxygen is replaced by a phosphonate P–C linkage. Treatment of intact TriMP derivatives 2a, 2b, 3a, and 7a with aqueous tetrabutylammonium hydroxide results in ring opening to linear triphosphate derivatives. X-ray crystal structures are provided for salts of 1, 2a, 3a, and 4.