N-Heterocyclic Carbenes with a N-2,4-Dinitrophenyl Substituent: Comparison with PPh3 and IPr
N-Heterocyclic Carbenes with a N-2,4-Dinitrophenyl Substituent: Comparison with PPh3 and IPr
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带有 N-2,4-二硝基苯基取代基的 N-杂环卡宾：与 PPh3 和 IPr 的比较
DOI：
10.1021/om300814f
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发表时间：
2012
期刊：
影响因子：
2.8
通讯作者：
Shuichi Oi
中科院分区：
文献类型：
--
作者：
Tetsuo Sato;Yoichi Hirose;Daisuke Yoshioka;Shuichi Oi
合成和表征了以2，4-二硝基苯基取代的N-杂环卡宾(NHC)。1-(2，4-二硝基苯基)-1H-咪唑(1)与1-溴-2，4-二硝基苯或三氟化甲酯反应，分别得到咪唑盐2a·Hbr或2b·HOTf，它们分别是1，3-bis(2，4-dinitrophenyl)-1H-imidazol-2-ylidene(2a)和1-(2，4-dinitrophenyl)-3-methyl-1H-imidazol-2-ylidene(2b)的前体。以2 a·HBr和2 b·HOTf为原料合成了Rh和Au配合物RhCl(2a)(Cod)[3a(Cod=1，5-环辛二烯)]、RhCl2b(Cod)(3b)、RhCl2a(CO)2(4a)、RhCl2b(CO)2(4b)和AuCl2a(5a)。红外光谱、核磁共振和结晶学分析表明，二氮磷取代基显著降低了碳氢化合物的σ供体能力，提高了其接受π的能力。此外，红外光谱还表明，Rh-二羰基络合物的平均CO伸缩频率与PPh_3相同。在Au(I)催化的环己烯氢烷氧基化反应中，Au络合物5a的催化活性明显高于AuCl(PPh_3)_5。对Au(I)络合物的计算分析支持实验数据，结果表明，5a的Au-Ccarbene-π-Back键相互作用能比5d的大17-20%。
Synthesis and characterization of N-heterocyclic carbenes (NHCs) bearing a 2,4-dinitrophenyl (DNP) substituent on an NHC framework were performed. The treatment of 1-(2,4-dinitrophenyl)-1H-imidazole (1) with 1-bromo-2,4-dinitrobenzene or methyl triflate afforded imidazolium salts2a·HBr or2b·HOTf, respectively, which were corresponding precursors of NHC ligands 1,3-bis(2,4-dinitrophenyl)-1H-imidazol-2-ylidene (2a) and 1-(2,4-dinitrophenyl)-3-methyl-1H-imidazol-2-ylidene (2b). Rh and Au complexesRhCl(2a)(cod) [3a(cod = 1,5-cyclooctadiene)], RhCl(2b)(cod) (3b), RhCl(2a)(CO)2(4a), RhCl(2b)(CO)2(4b), and AuCl(2a) (5a)were synthesized using2a·HBr and2b·HOTf. IR, NMR, and crystallographic analysis of the Rh complexes demonstrated that the DNP substituent remarkably decreased the σ-donating ability of the carbenic carbon and increased the π-accepting ability. In addition, IR spectroscopy of Rh dicarbonyl complexes revealed that the average CO stretching frequency of2awas equal to that of PPh3. Au complex5aexhibited a significantly higher catalytic activity than AuCl(PPh3)5din the Au(I)-catalyzed hydroalkoxylation of cyclohexene. The computational analysis of the Au(I) complexes supported the experimental data, and the results suggested that the Au–Ccarbeneπ-back-bonding interaction energy of5awas 17–20% larger than that of5d.