Efficient and Recyclable RuCl₃ ⋅ 3H₂O Catalyst Modified with Ionic Diphosphine for the Alkoxycarbonylation of Aryl Halides

A series of ionic (mono-/di-)phosphines (L2, L4, and L6) with structural similarity and their corresponding neutral counterparts (L1, L3, and L5) were applied to modulate the catalytic performance of RuCl₃ ⋅ 3H₂O. With the involvement of the ionic diphosphine (L4), in which the two phosphino-fragments were linked by butylene group, RuCl₃ ⋅ 3H₂O with advantages of low cost, robustness, and good availability was found to be an efficient and recyclable catalyst for the alkoxycarbonylation of aryl halides. The L4-based RuCl₃ ⋅ 3H₂O system corresponded to the best conversion of PhI (96 %) along with 99 % selectivity to the target product of methyl benzoate as well as the good generality to alkoxycarbonylation of different aryl halides (ArX, X=I and Br) with alcohols MeOH, EtOH, i-PrOH and n-BuOH. The electronic and steric effects of the applied phosphines, which were analyzed by the ³¹P NMR for ¹J³¹_P-⁷⁷_Se¹J measurement and single-crystal X-ray diffraction, were carefully co-related to the performance RuCl₃ ⋅ 3H₂O catalyst. In addition, the L4-based RuCl₃ ⋅ 3H₂O system could be recycled successfully for at least eight runs in the ionic liquid [Bmim]PF₆.