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首页> 外文期刊>Polyhedron: The International Journal for Inorganic and Organometallic Chemistry >Synthesis and characterization of a family of Co(II) triphenylamido-amine complexes and catalytic activity in controlled radical polymerization of olefins
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Synthesis and characterization of a family of Co(II) triphenylamido-amine complexes and catalytic activity in controlled radical polymerization of olefins

机译：Co（II）三苯基酰胺基-胺配合物家族的合成，表征以及烯烃受控自由基聚合中的催化活性

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摘要

The present work reports a new family of tripodal Co~(II) complexes bearing trianionic triphenylamidoamine ligands with a variety of pendant arms (aryl, acyl, alkyl). These complexes have been synthesized by the reaction of anhydrous CoC_(μ2) with the deprotonated ligands and exhibit stoichiometric and structural variation. The solid-state structures of these compounds reveal that in all cases the four nitrogen- atom residues of the ligands are coordinated to the metal center in a distorted trigonal-pyramidal geometry. In two cases, the presence of acetonitrile adds a fifth moiety to the coordination sphere. Among the aryl-armed Co~(II) reagents, [K(L~3)Co~(II)-NCMe]_n (1), [K(THF)_6][(L~5)Co~(II)]·1.5THF (2) and [K(NCMe)_3(L~(13)) Co~(II)-NCMe] (6), the two five-coordinate structures (1, 6) exhibit distorted trigonal bipyramidal geometries, with that of 6 being the least distorted. The four-coordinate species 2 is the only compound with a distinct anionic [(L~5)Co~(II)]-component, since the K~+ ion is solely coordinated by solvent molecules. The acyl-armed Co~(II) compounds [K(THF)_2(L~8)Co~(II)]n (3) and {[K_2(DMA)_3(L~(10))_2Co~(II) _2]·0.5Et_2O}n (5) are strictly four-coordinate species, with the carbonyl moieties oriented exo with respect to the cavity of the vacant coordination site. Finally, compound [K_2(L~9)_2Co~(II) _2]n (4) is the only example bearing an alkyl-armed ligand, and exhibits a geometry featuring a repeating -[Co(1)-K(1)-Co(2)-K(2)]_n- sequence. All compounds have been characterized by spectroscopic and electrochemical techniques. Compounds 1, 2, 4, and 6 show reversible or semi-reversible Co~(II)/Co~(III) redox couples, whereas the electron-deficient complexes 3 and 5 exhibit irreversible anodic waves. The catalytic reactivity of these complexes towards controlled radical polymerization (CRP) of styrene (St) and methyl methacrylate (MMA) has been studied and preliminary results are presented. Compounds 4 and 5 seem to be the most reactive with both monomers, giving high yields of polymers (60-86%), 3 efficiently induces styrene polymerization (90%), whereas 2 and 6 provide lower yields (12-16% for PS and 30-45% for PMMA). The steric factor seems to play an essential role, since Co~(II) compounds that feature a less hindered fifth coordination site show the highest reactivity and better control over polymerization. The polymers obtained are predominately syndiotactic, consistent with radical polymerization, with two exceptions (1, 2) that exhibit unusually high ratios of isotactic triads. Interestingly, in many cases, the polymers obtained feature bimodal distributions, while the molecular weight distributions are not very broad (1.40-2.00), and this strongly indicates that two parallel mechanisms may be in operation.
机译：本工作报告了一个新的三脚架Co〜（II）配合物家族，这些配合物带有带有各种侧链（芳基，酰基，烷基）的三阴离子三苯基氨基胺配体。这些配合物是通过无水CoC_（μ2）与去质子化的配体反应合成的，并且具有化学计量和结构变化。这些化合物的固态结构表明，在所有情况下，配体的四个氮原子残基均以扭曲的三角锥型几何结构与金属中心配位。在两种情况下，乙腈的存在会向配位球添加第五部分。在芳基武装的Co〜（II）试剂中，[K（L〜3）Co〜（II）-NCMe] _n（1），[K（THF）_6] [（L〜5）Co〜（II） ]·1.5THF（2）和[K（NCMe）_3（L〜（13））Co〜（II）-NCMe]（6）时，两个五坐标结构（1、6）呈现扭曲的三角双锥体几何形状，其中6失真最小。四配位物质2是唯一具有独特的阴离子[（L〜5）Co〜（II）]成分的化合物，因为K〜+离子仅由溶剂分子配位。酰基武装的Co〜（II）化合物[K（THF）_2（L〜8）Co〜（II）] n（3）和{[K_2（DMA）_3（L〜（10））_ 2Co〜（II ）_2]·0.5Et_2O} n（5）严格是四配位物种，羰基部分相对于空位配位位点的腔外向。最后，化合物[K_2（L〜9）_2Co〜（II）_2] n（4）是唯一一个带有烷基臂配体的例子，并且具有重复-[Co（1）-K（1） -Co（2）-K（2）] _ n-序列。所有化合物均已通过光谱和电化学技术表征。化合物1、2、4和6显示出可逆或半可逆的Co-（II）/ Co-（III）氧化还原对，而缺电子的配合物3和5显示出不可逆的阳极波。研究了这些配合物对苯乙烯（St）和甲基丙烯酸甲酯（MMA）的受控自由基聚合（CRP）的催化反应性，并给出了初步结果。化合物4和5似乎对两种单体都具有最高的反应活性，可提供高产率的聚合物（60-86％），化合物3可有效地引发苯乙烯聚合（90％），而化合物2和6的产率较低（PS的产率为12-16％）对于PMMA为30-45％）。空间因素似乎起着至关重要的作用，因为具有较少受阻的第五配位点的Co〜（II）化合物显示出最高的反应性和对聚合的更好控制。所获得的聚合物主要是间同立构的，与自由基聚合相符，只有两个例外（1、2），它们表现出不同比例的等规三单元组。有趣的是，在许多情况下，获得的聚合物具有双峰分布，而分子量分布不是很宽（1.40-2.00），这强烈表明可能存在两种平行的机理。

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