Dang Liang, Guo Jing, Song Haibin, Liu Binyuan, Wang Baiquan
State Key Laboratory of Elemento-Organic Chemistry, College of Chemistry, Nankai University, Tianjin 300071, China.
Dalton Trans. 2014 Dec 7;43(45):17177-83. doi: 10.1039/c4dt02198c.
Treatment of the o-hydroxyaryl imidazolium pro-ligands (2-OH-3,5-tBu2C6H2)(R)(C3H3N2)(+)Br(-) [R = Mes (1a), Ph (1b), iPr (1c), Me (1d)] with Ag2O afforded the corresponding silver complexes 2a-d. Subsequent metal-exchange reactions of 2a-d with [Pd(OAc)(8-Me-quin-H)]2 (3) yielded the desired C(sp(3)), N-chelated and o-aryloxide-NHC-ligated palladacycle complexes 4a-d in 60-80% yields. When the N-tert-butyl substituted o-hydroxyaryl imidazolium pro-ligand 1e reacted with 3 in the presence of K2CO3 in dioxane, the palladacycle complex 4e, in which the NHC adopted an abnormal binding (C4-bonding), was obtained in 20% yield. All these complexes were fully characterized using (1)H and (13)C NMR spectra, high-resolution mass spectrometry (HRMS), and elemental analysis. Single-crystal X-ray diffraction analysis results further confirmed the molecular structures of 4a-c and the abnormal binding of NHC in 4e. With methylaluminoxane (MAO) as the cocatalyst these palladacycles showed excellent catalytic activities of up to 10(7) g of PNB (mol of Pd)(-1) h(-1) in the addition polymerization of norbornene.
用氧化银处理邻羟基芳基咪唑鎓前体配体(2-OH-3,5-tBu₂C₆H₂)(R)(C₃H₃N₂)(⁺)Br⁻ [R = 均三甲苯基(1a)、苯基(1b)、异丙基(1c)、甲基(1d)]，得到相应的银配合物2a - d。2a - d与[Pd(OAc)(8-Me-quin-H)]₂ (3)随后进行的金属交换反应，以60 - 80%的产率得到了所需的C(sp³)、N螯合且邻芳氧基-NHC配位的钯环配合物4a - d。当N-叔丁基取代的邻羟基芳基咪唑鎓前体配体1e在碳酸钾存在下于二氧六环中与3反应时，以20%的产率得到了钯环配合物4e，其中NHC采取了异常配位(C4-键合)。所有这些配合物都通过¹H和¹³C NMR光谱、高分辨率质谱(HRMS)以及元素分析进行了全面表征。单晶X射线衍射分析结果进一步证实了4a - c的分子结构以及4e中NHC的异常配位。以甲基铝氧烷(MAO)作为助催化剂，这些钯环在降冰片烯的加成聚合反应中表现出高达10⁷ g PNB (mol Pd)⁻¹ h⁻¹的优异催化活性。
