Redox-Active Metallomacrocycles and Cyclic Metallopolymers: Photocontrolled Ring-Opening Oligomerization and Polymerization of Silicon-Bridged [1]Ferrocenophanes Using Substitutionally-Labile Lewis Bases as Initiators
Redox-Active Metallomacrocycles and Cyclic Metallopolymers: Photocontrolled Ring-Opening Oligomerization and Polymerization of Silicon-Bridged [1]Ferrocenophanes Using Substitutionally-Labile Lewis Bases as Initiators
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DOI：
10.1021/ja904928c
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发表时间：
2009-10-21
影响因子：
15
通讯作者：
Manners, Ian
中科院分区：
文献类型：
--
作者：
Herbert, David E.;Gilroy, Joe B.;Manners, Ian
在取代不稳定的刘易斯碱如4，4 '-二甲基-2，2'-联吡啶（Me（2）bpy）存在下，硅桥[1]二茂铁烷[Fe（eta-C5 H4）（2）SiMe 2]（1）的辐照通过铁-β键的断裂引发开环聚合和低聚。通过柱色谱法分离并充分表征了环状聚二茂铁基硅烷c-PFS（PFS = [Fe（eta-C5 H4）（2）SiMe 2]（n））和一系列环状低聚物（2（2）-2（7））的分布。发现不同的温度和浓度影响分子量分布和聚合物与低聚物产物的比率，使得能够形成分子量> 100 kDa的c-PFS。发现环状聚合物样品具有较低的流体动力学半径和粘度以及较高的玻璃化转变温度，与类似分子量的线性PFS对应物（I-PFS）相比。与类似分子量的I-PFS结晶样品相比，c-PFS形成较小的球晶，通过偏光显微镜观察到，而来自较低分子量I-1的广角X射线散射（WAXS）图案显示，发现PFS不同于来自较高分子量样品的PFS，对于c-PFS的较低和较高分子量样品获得的那些是相同的，并且类似于高分子量I-PFS的衍射图案。的循环和差分脉冲伏安法进行了研究，并发现取决于是否低聚物包含一个奇数或偶数的二茂铁单元。与线性类似物相比，对于含有偶数个铁中心的环状低聚物，观察到两个不同强度的可逆氧化还原过程，而对于含有奇数个铁中心的环状低聚物，观察到三个不同强度的可逆氧化还原过程。随着低聚物链长的增加，所有环状低聚物的电化学行为接近环状和线性高分子量聚合物。
Irradiation of silicon-bridged [1]ferrocenophane [Fe(eta-C5H4)(2)SiMe2] (1) in the presence of substitutionally labile Lewis bases such as 4,4'-dimethyl-2,2'-bipyridine (Me(2)bpy) initiates ring-opening polymerization and oligomerization via cleavage of an iron-cyclopentadienyl bond. A distribution of cyclic polyferrocenylsilane c-PFS (PFS = [Fe(eta-C5H4)(2)SiMe2](n)) and a series of cyclic oligomers (2(2)-2(7)) were isolated by column chromatography and fully characterized. Varying temperature and concentration were found to influence the molecular weight distribution and the ratio of polymer to oligomer products, enabling the formation of c-PFS with molecular weights > 100 kDa. Cyclic polymer samples were found to possess lower hydrodynamic radii and viscosity and higher glass transition temperatures than those of their linear PFS counterparts (I-PFS) of comparable molecular weight Compared with crystalline samples of I-PFS of similar molecular weights, c-PFS formed smaller spherulites, as observed by polarizing optical microscopy While the wide-angle X-ray scattering (WAXS) patterns from lower molecular weight I-PFS were found to differ from those from higher molecular weight samples, those obtained for lower and higher molecular weight samples of c-PFS are identical and resemble diffraction patterns of high molecular weight I-PFS The electrochemical behavior of each cyclic oligomer 2(2)-2(7) was studied by cyclic and differential pulse voltammetry and was found to depend on whether the oligomer contains an odd or even number of ferrocene units. In contrast to linear analogs, two reversible redox processes of varying intensities were observed for cyclic oligomers containing an even number of iron centers, while three reversible redox processes of varying intensities were observed for cyclic oligomers containing an odd number of iron centers As the oligomer chain length increased, the electrochemical behavior of all cyclic oligomers approached that of both cyclic and linear high molecular weight polymers.