Oxidation of Alcohols to Carbonyl Compounds Catalyzed by Oxo-Bridged Dinuclear Cerium Complexes with Pentadentate Schiff-Base Ligands under a Dioxygen Atmosphere
Oxidation of Alcohols to Carbonyl Compounds Catalyzed by Oxo-Bridged Dinuclear Cerium Complexes with Pentadentate Schiff-Base Ligands under a Dioxygen Atmosphere
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DOI：
10.1021/acscatal.8b01718
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发表时间：
2018-06
期刊：
影响因子：
12.9
通讯作者：
Satoru Shirase;Koichi Shinohara;H. Tsurugi;K. Mashima
中科院分区：
文献类型：
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作者：
Satoru Shirase;Koichi Shinohara;H. Tsurugi;K. Mashima
合成了一系列含五齿席夫碱配体的铈（III）3-L1-3-L9离子单核和中性双核配合物，表征了其结构，并将其用作无氧乙醇氧化反应的催化剂. Ce（NO3）3·6 H2O与邻叔丁基取代的位阻配体NH的反应（CH2CH2N-[CHC6H2-3-（tBu）-5-R2 -2-OH）2（对于L1 H2，R2 = tBu;对于L2 H2，R2 = OMe;对于L_3H_2，R_2 = H），在三乙胺存在下得到相应的阴离子铈配合物[HNEt_3][Ce（L_1 -3）（NO_3）_2]。（3-L1-3-L3），而与空间位阻较小的配体如NH（CH2CH2N-CHC6H2-3-R1-5-R2-2-OH）2（对于L4 H2，R1 = OMe且R2 = H;对于L5 H2，R1 = H且R2 = tBu;对于L 6 H2，R1 = H且R2 = OMe;对于L7 H2，R1 = H且R2 = H;对于L 8H 2，R1 = H且R2 = NO2;对于L_9H_2，R_1 = tBu，R_2 = NO_2），得到中性双核配合物[Ce（L_4 -9）（NO_3）]_2（3-L_4 -3-L_9）。在这些新制备的配合物中，配合物3-L1被选为最佳的催化剂。
Ionic mononuclear and neutral dinuclear complexes of cerium(III) 3-L1–3-L9 bearing a series of dianionic pentadentate Schiff-base ligands were synthesized, characterized, and used as catalysts for N-oxyl radical-free aerobic alcohol oxidation. Reactions of Ce(NO3)3·6H2O with o-tert-butyl-substituted sterically hindered ligands NH(CH2CH2N═CHC6H2-3-(tBu)-5-R2-2-OH)2 (for L1H2, R2 = tBu; for L2H2, R2 = OMe; and for L3H2, R2 = H) in the presence of triethylamine afforded the corresponding anionic cerium complexes [HNEt3][Ce(L1–3)(NO3)2] (3-L1–3-L3), whereas complexation with sterically less hindered ligands, such as NH(CH2CH2N═CHC6H2-3-R1-5-R2-2-OH)2 (for L4H2, R1 = OMe and R2 = H; for L5H2, R1 = H and R2 = tBu; for L6H2, R1 = H and R2 = OMe; for L7H2, R1 = H and R2 = H; for L8H2, R1 = H and R2 = NO2; and for L9H2, R1 = tBu and R2 = NO2), afforded neutral dinuclear complexes [Ce(L4–9)(NO3)]2 (3-L4–3-L9). Among these newly prepared complexes, complex 3-L1 was selected as the best catalyst for oxidizing primary...