Oxime-based salen-type tetradentate ligands with high stability against imine metathesis reaction
Oxime-based salen-type tetradentate ligands with high stability against imine metathesis reaction
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DOI：
10.1021/jo048030y
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发表时间：
2005-03-04
影响因子：
3.6
通讯作者：
Nabeshima, T
中科院分区：
文献类型：
--
作者：
Akine, S;Taniguchi, T;Nabeshima, T
虽然salen及其类似物是无机和有机金属化学中用途广泛的螯合配体，但由于C=N键的重组，由两个不同水杨醛亚胺部分组成的不对称salen衍生物的合成是困难的。为了开发稳定的salen型配体类似物，我们以O-烷基肟取代亚胺部分，合成了一系列新的salamo（= 1，2-bis（salicylideneaminoxy）ethane）配体。从相应的水杨醛2a-h以64-88%的产率制备了8个无色晶体的salamo配体la-h。la-c的晶体结构表明肟-OH形式比酮-NH形式更占优势。2a-e与过量的1，2-双（氨氧基）乙烷反应得到59- 86%的单肟3a-e，其进一步与不同的水杨醛反应得到51- 70%的不对称salamo配体4-8，为稳定的晶体。当salamo衍生物1a和1b的混合物在40 ℃下在H2O/MeCN（5：95）中处理时，没有反应发生。然而，salen衍生物9a和9 b的复分解反应在2小时内完成，得到统计混合物。单肟3b比难以分离的单亚胺11稳定得多。这些结果表明salamo衍生物1和前体3具有极高的稳定性。
Although salen and its analogues are versatile chelate ligands in inorganic and organometallic chemistry, synthesis of unsymmetrical salen derivatives consisting of two different salicylideneimine moieties is difficult because of the C=N bond recombination. To develop stable analogues of salen-type ligands, we synthesized a series of new ligands salamo (=1,2-bis(salicylideneaminooxy)ethane) on the basis of O-alkyl oxime instead of the imine moiety. Eight salamo ligands la-h were prepared in 64-88% yields as colorless crystals from the corresponding salicylaldehydes 2a-h. The crystal structure of la-c suggests that the oxime-OH form is more predominant than the keto-NH form. The reaction of 2a-e with excess 1,2-bis(aminooxy)ethane gave monooximes 3a-e in 59-86%, which further reacted with a different salicylaldehyde to afford unsymmetrical salamo ligands 4-8 as stable crystals in 51-70%. No reaction took place when a mixture of salamo derivatives la and 1b was treated at 40 degreesC in H2O/MeCN (5:95). However, the metathesis reaction of salen derivatives 9a and 9b completed in 2 h to give a statistical mixture. Monooxime 3b was much more stable than monoimine 11 which is difficult to be isolated. These results indicate the extremely high stability of the salamo derivatives 1 and precursors 3.