Synthesis, Crystal Structures, and Catalytic Activity of Dicopper(II) Complexes with Dinucleating Tetraimidazole Ligands [Cu2(RO)(mbipl)](ClO4)2 (R = Me, Et, 2-Pr; Hmb

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• 作者：Masahito Kodera ; Norihisa Terasako ; Toshio Kita ; Yoshimitsu Tachi ; Koji Kano ; Mikio Yamazaki ; Masayuki Koikawa ; and Tadashi Tokii
• 刊名：Inorganic Chemistry
• 出版年：1997
• 出版时间：August 27, 1997
• 年：1997
• 卷：36
• 期：18
• 页码：3861 - 3868
• 全文大小：288K
• 年卷期：v.36,no.18(August 27, 1997)
• ISSN：1520-510X

文摘

Synthesis, crystal structures, and catalytic activity are reportedfor dinuclear copper(II) complexes of newdinucleating tetraimidazole ligands,1,5-bis[bis[(1-methyl-4-imidazolyl)methyl]amino]-3-pentanol(Hmbipl) and1,5-bis[bis[(1-isopropyl-4-imidazolyl)methyl]amino]-3-pentanol(Hpbipl). These ligands have been prepared bya reductive coupling of 1,5-diamino-3-pentanol with 4 equiv of1-alkyl-4-formylimidazole (alkyl = methyl andisopropyl) by using sodium cyanoborohydride in quantitative yields.The ligand Hmbipl forms[Cu₂(MeO)(mbipl)](ClO₄)₂ (1) in MeOH.The methoxide bridge of 1 is easily exchanged with EtOHand 2-PrOH duringrecrystallization from such solvents, yielding ethoxide- and2-propoxide-bridged complexes[Cu₂(RO)(mbipl)](ClO₄)₂ (R = Et, 2; R = 2-Pr,3). The ligand Hpbipl forms[Cu₂(MeO)(pbipl)](ClO₄)₂(4) in MeOH. Compounds1-4 have been characterized by elementalanalyses, FAB mass, electronic absorption, and IR spectra,magneticsusceptibilities, and cyclic voltammograms. Crystal structures of2·2MeCN and3·CH₂Cl₂ have beendeterminedby X-ray analyses, showing that the coordination geometry about eachcopper ion in 2 and 3 is distortedtrigonalbipyramidal. Compounds 1-4 catalyze thequantitative oxidation of 2,4-di-tert-butylphenol (DBP) to3,3',5,5'-tetra-tert-butyl-2,2'-dihydroxybiphenyl withH₂O₂. A hydroperoxodicopper(II)complex 5 which is generatedfrom 4 as an active intermediate is detected by UV-visspectroscopy. Compound 4 shows the highestactivityamong the present complexes because of its high reaction rate and highdurability. Kinetic studies show that thereaction is first order with respect to both DBP and the catalyst.The second-order rate constant, k₂, is 5.3M^-1s^-1. It seems that the bulkyN-isopropyl groups enhance the catalytic activity of4.