Coordination chemistry and reactivity of monomeric alkoxides and amides of magnesium and zinc supported by the diiminato ligand CH(CMeNC6H3-2,6-iPr2)2.: A comparative study
Coordination chemistry and reactivity of monomeric alkoxides and amides of magnesium and zinc supported by the diiminato ligand CH(CMeNC6H3-2,6-iPr2)2.: A comparative study
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DOI：
10.1021/ic020148e
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发表时间：
2002-05-20
影响因子：
4.6
通讯作者：
Phomphrai, K
中科院分区：
文献类型：
--
作者：
Chisholm, MH;Gallucci, J;Phomphrai, K
报道了一系列密切相关的镁和锌化合物的制备和表征：LMg((NPr2)-Pr-i)(THF), 1； LZn((NPr2)-Pr-i), 2; LMg((OBu)-Bu-t)(THF), 3; LZn((OBu)-Bu-t), 4;和LZn(OSiPh3)(THF)，6；其中 L = CH-(CMeNC6H3-2,6-Pr-i(2))(2)。它们的动态溶液行为已通过变温 NMR 研究进行了检验，并揭示了 THF 在甲苯-d(8) 或 CD2Cl2 中可逆解离，并且通过解离过程与游离 THF 进行交换，化合物 1-4 和 6 均引发并随后维持丙交酯的开环聚合 (ROP)。对于一系列相关的化合物 LMX(THF)(n)，其中 n = 1 或 0，初始开环速率遵循 M = Mg > Zn 和 X = (OBu)-Bu-t > (NPr2)-Pr-i > NSi2Me6 > OSiPh3 的顺序。在 25 ℃ 的 THF 中，对于 M = Mg 和 Zn，化合物 3 和 4 分别在 5 和 80 分钟内聚合 100 当量的外消旋丙交酯，转化率达到 >95%，产量约为 100%。 90% 异同立构 PLA，（isi + sis 四分体）。反应在二氯甲烷中进行得更快，但对于 M = Mg，在酯交换之前由外消旋丙交酯 (3iii:2isi.sii.sis:iis) 形成伯努利分布的四分体。通过 VT H-1 NMR 光谱研究了 L-LA 在甲苯-d(8) 和 THF-d(8) 中通过 3 和 4 聚合：锌的静止态被认为是类似于 LZn(eta(2)-OCHMeC(O)OMe) 的单体物质，而镁络合物似乎是二聚 LMg(mu-OP)(2)MgL。尽管酰胺镁 1 通过烯丙基质子夺取实现开环并形成二聚化合物 [LMg(mu-OC6H9)](2), 7，但这些化合物均不能引发环氧丙烷 (PO) 或环己烯氧化物 (CHO) 的均聚。还描述了与二氧化碳的反应，以及 (LZnO2CNPr2)-Pr-i, 8 的表征，该化合物在室温下对 CHO 和 PO 呈惰性。所有化合物均对水解敏感，并且 LZn(mu-OH)(2)ZnL, 5 已从化合物 4 的水解中分离出来。报告了化合物 1-5、7 和 8 的晶体和分子结构。这些结果与 Coates 等人最近报道的结果进行了比较。
The preparation and characterization of a series of closely related magnesium and zinc compounds are reported: LMg((NPr2)-Pr-i)(THF), 1; LZn((NPr2)-Pr-i), 2; LMg((OBu)-Bu-t)(THF), 3; LZn((OBu)-Bu-t), 4; and LZn(OSiPh3)(THF), 6; where L = CH-(CMeNC6H3-2,6-Pr-i(2))(2). Their dynamic solution behavior has been examined by variable-temperature NMR studies and reveals that THF reversibly dissociates in toluene-d(8) or CD2Cl2 and that exchange with free THF occurs by a dissociative process, Compounds 1-4 and 6 all initiate and subsequently sustain ring-opening polymerization (ROP) of lactides. For a related series of compounds LMX(THF)(n), where n = 1 or 0, the rate of initial ring-opening follows the order M = Mg > Zn and X = (OBu)-Bu-t > (NPr2)-Pr-i > NSi2Me6 > OSiPh3. In THF at 25 degreesC, compounds 3 and 4 polymerize 100 equiv of rac-lactide to >95% conversion in 5 and 80 min for M = Mg and Zn, respectively, and yield ca. 90% heterotactic PLA, (isi + sis tetrads). The reactions proceed faster in methylene chloride, but for M = Mg, a Bernoulian distribution of tetrads is formed from rac-lactide (3iii:2isi.sii.sis:iis) prior to trans-esterification. Polymerization of L-LA in toluene-d(8) and THF-d(8) by 3 and 4 have been studied by VT H-1 NMR spectroscopy: the resting state for zinc is proposed to be a monomeric species akin to LZn(eta(2)-OCHMeC(O)OMe), whereas the magnesium complex appears to be dimeric LMg(mu-OP)(2)MgL. None of the compounds is capable of initiating homopolymerization of propylene oxide (PO) or cyclohexene oxide (CHO), although the magnesium amide 1 effects ring-opening by allylic proton abstraction and the dimeric compound [LMg(mu-OC6H9)](2), 7, is formed. Reactions with carbon dioxide are also described, along with the characterization of (LZnO2CNPr2)-Pr-i, 8, which is shown to be inert with respect to CHO and PO at room temperature. All the compounds are hydrolytically sensitive, and LZn(mu-OH)(2)ZnL, 5, has been isolated from hydrolysis of compound 4. The crystal and molecular structures are reported for compounds 1-5, 7, and 8. These results are compared with those recently reported by Coates et al.