摘要/Abstract

通过对双齿膦配体的单P原子定向甲基化, 合成了两种离子型“叔膦-季鏻鎓Lewis酸”双功能配体L2和L3, 该类双功能配体分子结构中既含有与过渡金属配位的叔膦基团, 又含有具Lewis酸的季鏻鎓基团. 研究结果表明, 在合成气的体积比(CO/H₂)为4∶1时, 双功能配体L2修饰的[Ir(COD)Cl]₂催化剂高效催化烯烃的“氢甲酰化-缩醛化”串联反应, 1-辛烯的转化率为98%, 缩醛的选择性高达86%, 其催化活性好于同等条件下的Rh催化剂. 双功能配体L2与[Ir(COD)Cl]₂原位构建的共催化体系的催化效果远优于Ir(I)配合物和季鏻鎓Lewis酸的物理混合; 同时还表现出较好的底物普适性. 此外, 由于双功能配体L2的高极性, 其修饰的Ir催化剂可以顺利实现与正己烷溶液的分离, 从而实现催化剂的回收循环使用.
关键词: 氢甲酰化, 缩醛化, 串联反应, 双功能配体, 铱催化剂
The ionic bi-functional ligands of L2 and L3 in combination of a phosphine with a Lewis acidic phosphonium were synthesized through selective quaternized by MeI at the one P-position of the bi-dentate ligands. Due to the separation by the rigid ring, the incorporated -PPh₂ and the Lewis acidic phosphonium were well retained without quenching problem. In the bi-functional ligands, the phosphine group could coordinate with transition metals, the phosphonium group could present Lewis acidic. The Ir(I)-complex modified by the “phosphino-phosphonium” bi-functional ligand ( L2) was used to catalyze the tandem hydroformylation-acetalization of olefins. Under the optimized conditions ([Ir(COD)Cl]₂ 0.025 mmol, L2 0.025 mmol, 1-octene 5.0 mmol, methanol 5.0 mL, N-methyl pyrrolidone 2.0 mL, V_CO/V_H2=4∶1 4.0 MPa, temperature 120 ℃, reaction time 8 h), the conversion of 1-octene was 97% with the selectivity of acetals up to 86%, which was analyzed by GC and GC-MS. In this system, the activity of Ir catalyst was better than that of Rh catalyst at same conditions. It was found thatL2-modified [Ir(COD)Cl]₂ could also efficiently accelerate this tandem reaction, which proved more effective than the ligands lacking phosphonium or the mechanical mixtures of the individual functional groups independently. It was believed that, in L2, the phosphonium not only acted as a Lewis acid organocatalyst to drive the sequential acetalization of aldehydes, but also contributed to the synergetic catalysis for the preceding hydroformylation through stabilizing the Ir-acyl intermediate with the phosphine cooperatively. The L2-[Ir(COD)Cl]₂ system is also generally applied to the tandem hydroformylation-acetalization reaction of a wide range of olefins in different alcohols, give the yields of products in the range of 45%~87%. Advantageously, as an ionic ligand with high polarity, L2-based Ir(I)-catalyst could be precipitated by n-hexane upon completion to fulfil the recovery and recycling uses of transition metal catalysts.
Key words: hydroformylation, acetalization, tandem reaction, bi-functional ligand, Ir-catalyst


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