Nucleophilic Addition of CH, NH, and OH Bonds to the Phosphadiazonium Cation and Interpretation of ³¹P Chemical Shifts at Dicoordinate Phosphorus Centers

The phosphadiazonium cation [Mes*NP]⁺ reacts quantitatively with the fluorenylide anion, Mes*NH₂, and Mes*OH (Mes* = 2,4,6-tri-tert-butylphenyl), resulting in formal insertion of the N−P moiety into the H−Y (Y = C, N, O) bonds. Specifically, reaction of Mes*NPCl with fluorenyllithium gives the aminofluorenylidenephosphine [crystal data:  C₃₁H₃₈NP, monoclinic, P2₁/c, a = 9.568(8) Å, b = 24.25(2) Å, c = 11.77(1) Å, β = 101.38(8)°, Z = 4]. Similarly, reaction of [Mes*NP][GaCl₄] with Mes*NH₂ gives the diaminophosphenium salt [Mes*N(H)PN(H)Mes*][GaCl₄] [crystal data:  C₃₆H₆₀Cl₄GaN₂P, monoclinic, C2/c, a = 24.921(2) Å, b = 10.198(4) Å, c = 16.445(2) Å, β = 93.32(1)°, Z = 4], and reaction with Mes*OH gives the first example of an aminooxyphosphenium salt [Mes*N(H)POMes*][GaCl₄]. It is proposed that the reactions involve nucleophilic attack at phosphorus followed by a 1,3-hydrogen migration from Y to N. Experimental evidence for the formation of σ-complex intermediates is provided by the isolation of [Mes*NP−PPh₃][SO₃CF₃] [crystal data:  C₃₇H₄₄F₃NO₃P₂S, triclinic, P1̄, a = 10.663(1) Å, b = 19.439(1) Å, c = 10.502(1) Å, α = 103.100(7)°, β = 113.311(7)°, γ = 93.401(7)°, Z = 2]. As part of the unequivocal characterization of the aminooxyphosphenium salt, detailed solid-state ³¹P NMR studies and GIAO calculations on the phosphenium cations have been performed. Contrary to popular belief, the phosphorus shielding in dicoordinate cations is not caused by the positive charge but results from efficient mixing between the phosphorus lone pair and π* orbitals.