P_2 Addition to Terminal Phosphide M≡P Triple Bonds: A Rational Synthesis of cyclo-P_3 Complexes

摘要

The diphosphaazide complex (Mes~*NPP)Nb(N[Np]Ar)_3 (Mes~* = 2,4,6-tri-tert-butylphenyl, Np = neopentyl, Ar = 3,5-Me_2C_6H_3), 1, has previously been reported to lose the P_2 unit upon gentle heating, to form (Mes~*N)Nb(N[Np]Ar)_3, 2. The first-order activation parameters for this process have been estimated here using an Eyring analysis to have the values ΔH~* = 19.6(2) kcal/mol and ΔS~* = -14.2(5) eu. The eliminated P_2 unit can be transferred to the terminal phosphide complexes P≡M(N[~iPr]Ar)_3, 3-M (M = Mo, W), and [P≡Nb(N[Np]Ar)_3]~-, 3-Nb, to give the cyclo-P_3 complexes (P_3)M(N[~iPr]Ar)_3 and [(P_3)Nb(N[Np]Ar)_3]~-. These reactions represent the formal addition of a P≡P triple bond across a M≡P triple bond and are the first efficient transfers of the P_2 unit to substrates present in stoichiometric quantities. The related complex (OC)_5W(Mes~*NPP)Nb(N[Np]Ar)_3, 1-W(CO)_5, was used to transfer the (P_2)W(CO)-5 unit in an analogous manner to the substrates 3-M (M = Mo, W, Nb) as well as to [(OC)_5WP=Nb(N[Np]Ar)_3]~-. The rate constants for the fragmentation of 1 and 1-W(CO)_5 were unchanged in the presence of the terminal phosphide 3-Mo, supporting the hypothesis that molecular P_2 and (P_2)W(CO)_5, respectively, are reactive intermediates. In a reaction related to the combination of P≡P and M≡P triple bonds, the phosphaalkyne AdC≡P (Ad = 1-adamantyl) was observed to react with 3-Mo to generate the cyclo-CP_2 complex (AdCP_2)Mo(N[~iPr]Ar)_3. Reactions of the electrophiles Ph_3SnCI, Mes~*NPCI, and AdC(O)CI with the anionic, nucleophilic complexes [(OC)_5W(P_3)Nb(N[Np]Ar)_3]~- and [{(OC)_5W}_2(P_3)Nb(N[Np]Ar)_3]~- yielded coordinated η~2-triphosphirene ligands. The Mes~*NPW(CO)_5 group of one such product engages in a fluxional ring-migration process, according to NMR spectroscopic data. The structures of (OC)_5W(P_3)W(N[~iPr]Ar)_3, [(Et_2O)Na][{(OC)_5W}_2-(P_3)Nb(N[Np]Ar)_3], (AdCP_2)Mo(N[~iPr]Ar)_3, (OC)_5W(Ph_3SnP_3)Nb(N[Np]Ar)_3, Mes~*NP(W(CO)_5)P_3Nb(N[Np]Ar)_3, and {(OC)_5W}_2AdC(O)P_3Nb(NrNplAr)_3, as determined by X-ray crystallography, are discussed in detail.