A π-conjugated quinonediimine ligand possessing two terminal redox-active ferrocenyl groups, N,N′-bis(4′-ferrocenylcarboxamide)phenyl}-1,4-benzoquinonediimine (Lox), was synthesized. The quinonediimine ligand Lox was reduced to Lred composed of the phenylenediamine moiety on treatment with hydrazine hydrate. The reaction of Lox with the palladium(II) complex 1 bearing the N,N′-bis(2-phenylethyl)-2,6-pyridinedicarboxamide ligand afforded the multimetallic complex 2. Variable temperature 1H NMR studies of 2 indicated the existence of syn and anti isomers, in which the anti isomer is enthalpically more favorable than the syn isomer in CD2Cl2 by 0.9 kcal mol−1, but entropically less favorable by 2.6 cal mol−1 K−1 from the van’t Hoff plot. The redox function of the quinonediimine moiety is modulated by complexation with 1. The complex 2 showed three separate redox waves, which are assignable to the successive one-electron reduction of the quinonediimine moiety and oxidation of the two terminal ferrocenyl groups. Chemical reduction of 2 in CH2Cl2 with [Co(Cp)2] resulted in the appearance of ESR signals with weak 105Pd coupling centered around g = 2.004. The unpaired electron appears to locate mostly on the quinonediimine moiety with some delocalization onto the palladium center.
一种具有两个末端氧化还原活性
二茂铁基团的π-共轭醌二
亚胺配体--N,N′-双(4′-
二茂铁甲酰胺)苯基}-1,4-苯醌二
亚胺(Lox)被合成出来。醌二
亚胺配体 Lox 经
肼水合物处理后被还原成由
苯二胺分子组成的 Lred。Lox 与带有 N,N′-双(2-苯基乙基)-2,6-
吡啶二甲酰胺
配体的
钯(II)络合物 1 反应,得到多
金属络合物 2。对 2 的变温 1H NMR 研究表明,其中存在同分异构体和反异构体,在 CD2Cl2 中,反异构体的焓值比同分异构体高 0.9 kcal mol-1,但从范特霍夫曲线图来看,熵值比同分异构体低 2.6 cal mol-1 K-1。醌二
亚胺分子的氧化还原功能受与 1 的络合物的调节。络合物 2 显示出三个独立的氧化还原波,可归因于醌二
亚胺分子的连续单电子还原和两个末端
二茂铁基团的氧化。用[Co(Cp)2]在
CH2Cl2 中对 2 进行
化学还原后,出现了以 g = 2.004 为中心的弱 105Pd 耦合 ESR 信号。未配对的电子似乎主要位于醌二
亚胺分子上,但也有一些分散到
钯中心上。