Regioselective functionalization of iminophosphoranes through Pd-mediated C–H bond activation: C–C and C–X bond formation

Abstract

The orthopalladation of iminophosphoranes [R₃PN–C₁₀H₇-1] (R₃ = Ph₃1, p-Tol₃2, PhMe₂3, Ph₂Me 4, N–C₁₀H₇-1 = 1-naphthyl) has been studied. It occurs regioselectively at the aryl ring bonded to the P atom in 1 and 2, giving endo-[Pd(μ-Cl)(C₆H₄-(PPh₂N-1-C₁₀H₇)-2)-κ-C,N]₂ (5) or endo-[Pd(μ-Cl)(C₆H₃-(P(p-Tol)₂N–C₁₀H₇-1)-2-Me-5)-κ-C,N]₂ (6), while in 3 the 1-naphthyl group is metallated instead, giving exo-[Pd(μ-Cl)(C₁₀H₆-(NPPhMe₂)-8)-κ-C,N]₂ (7). In the case of 4, orthopalladation at room temperature affords the kinetic exo isomer [Pd(μ-Cl)(C₁₀H₆-(NPPh₂Me)-8)-κ-C,N]₂ (11exo), while a mixture of 11exo and the thermodynamic endo isomer [Pd(μ-Cl)(C₆H₄-(PPhMeN–C₁₀H₇-1)-2)-κ-C,N]₂ (11endo) is obtained in refluxing toluene. The heating in toluene of the acetate bridge dimer [Pd(μ-OAc)(C₁₀H₆-(NPPh₂Me)-8)-κ-C,N]₂ (13exo) promotes the facile transformation of the exo isomer into the endo isomer [Pd(μ-OAc)(C₆H₄-(PPhMeN–C₁₀H₇-1)-2)-κ-C,N]₂ (13endo), confirming that the exo isomers are formed under kinetic control. Reactions of the orthometallated complexes have led to functionalized molecules. The stoichiometric reactions of the orthometallated complexes [Pd(μ-Cl)(C₁₀H₆-(NPPhMe₂)-8)-κ-C,N]₂ (7), [Pd(μ-Cl)(C₆H₄-(PPh₂NPh)-2)]₂ (17) and [Pd(μ-Cl)(C₆H₃-(C(O)NPPh₃)-2-OMe-4)]₂ (18) with I₂ or with CO results in the synthesis of the ortho-halogenated compounds [PhMe₂PN–C₁₀H₆–I-8] (19), [I–C₆H₄-(PPh₂NPh)-2] (21) and [Ph₃PNC(O)C₆H₃–I-2-OMe-5] (23) or the heterocycles [C₁₀H₆-(NPPhMe₂)-1-(C(O))-8]Cl (20), [C₆H₅-(NPPh₂-C₆H₄–C(O)-2]ClO₄ (22) and [C₆H₃-(C(O)-1,2-N–PPh₃)-OMe-4]Cl (24).