Galactose Oxidase Models: Creation and Modification of Proton Transfer Coupled to Copper(II) Coordination Processes in Pro-Phenoxyl Ligands
Galactose Oxidase Models: Creation and Modification of Proton Transfer Coupled to Copper(II) Coordination Processes in Pro-Phenoxyl Ligands
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DOI：
10.1002/ejic.200600286
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发表时间：
2006-09
影响因子：
2.3
通讯作者：
F. Michel;F. Thomas;S. Hamman;C. Philouze;E. saint-Aman;J. Pierre
中科院分区：
文献类型：
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作者：
F. Michel;F. Thomas;S. Hamman;C. Philouze;E. saint-Aman;J. Pierre
合成了2个吡啶基和1个4-（苯并咪唑-2-基）-2-叔丁基苯酚（HL H）和1个2-叔丁基-4-（n -甲基苯并咪唑-2-基）苯酚（HL Me）单元的三足配体。它们具有一个氮氧供体集，已知比相应的氮氧供体单元更有效地稳定苯氧基。一摩尔等量的Cu(clo4) 2·6h2o与·HL H或HL Me反应，通过与铜（II）配位耦合的质子转移反应，生成两性离子苯并咪唑-苯酚配合物[Cu II (HL H)] 2+和[Cu II (HL Me)] 2+。在[Cu II (HL H)] 2+和[Cu II (HL Me)] 2+中加入HClO 4生成苯并咪唑-苯酚配合物[Cu II (h2 L H)] 3+和[Cu II (h2 L Me)] 2+，而加入NEt 3则分别生成苯并咪唑-苯酚配合物[Cu II (HL H)] 2+和[Cu II (L Me)] 2+。由于苯并咪唑取代基的强吸出作用，苯酚的pK值非常低。铜（II）配合物的x射线晶体分析表明，轴向苯酚的去质子化迫使金属从方形平面向氧原子移动，并且一个（或两个）Cu-N吡啶的赤道键长度增加。通过电化学或在HL H或HL Me中加入两摩尔等量的铜（II），制备了铜（II）苯氧基[Cu II (HL H)] 3+和[Cu II (HL Me)] 3+。在这些条件下，从未观察到含有两个吡啶基和一个2,4-二叔丁基苯酚基团的三脚配体形成自由基。这种差异可以用质子转移机制和氧化还原电位来解释。
Two tripodal ligands containing two pyridyl and one 4-(benzimidazol-2-yl)-2-tert-butylphenol (HL H ) and one 2-tertbutyl-4-(N-methylbenzimidazol-2-yl)phenol (HL Me ) unit have been synthesized. They possess a N 3 O donor set that is known to stabilize phenoxyl radicals more efficiently than the corresponding N 2 O 2 donor unit. Reaction of one molar equiv. of Cu(ClO 4 ) 2 ·6H 2 O with·HL H or HL Me affords the zwitterionic benzimidazolium phenolate complexes [Cu II (HL H )] 2+ and [Cu II (HL Me )] 2+ via a proton transfer reaction coupled to copper(II) coordination. Addition of HClO 4 to [Cu II (HL H )] 2+ and [Cu II (HL Me )] 2+ results in the formation of the benzimidazolium phenol complexes [Cu II (H 2 L H )] 3+ and [Cu II (H 2 L Me )] 2+ , while addition of NEt 3 affords the benzimidazol-phenolate complexes [Cu II (L H )] 2+ and [Cu II (L Me )] 2+ , respectively. The phenol's pK a is remarkably low due to the strong withdrawing effect of the benzimidazolium substituent. X-ray crystallographic analysis of the copper(II) complexes shows that deprotonation of the axial phenol forces the metal to move out of the square plane towards the oxygen atom, and one (or two) Cu-N pyridine equatorial bond length increases. The copper(II) phenoxyl species [Cu II (HL H )] 3+ and [Cu II (HL Me )] 3+ were prepared electrochemically, or by addition of two molar equiv. of copper(II) to HL H or HL Me . Under these conditions, radical formation has never been observed for tripodal ligands containing two pyridyl and one 2,4-di-tert-butylphenol group. This difference is explained in terms of the proton transfer mechanism and redox potentials.