Simple strategy for the immobilization of dirhodium tetraprolinate catalysts using a pyridine-linked solid support
Simple strategy for the immobilization of dirhodium tetraprolinate catalysts using a pyridine-linked solid support
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DOI：
10.1021/ja0393067
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发表时间：
2004-04-07
影响因子：
15
通讯作者：
Nagashima, T
中科院分区：
文献类型：
--
作者：
Davies, HML;Walji, AM;Nagashima, T
在具有吡啶附着的高交联聚苯乙烯树脂存在下，四羧酸二钠很容易在搅拌下固定。系统的研究表明，聚合物主链、连接体、末端吡啶基团和催化剂结构都是影响钯催化剂固定化效率的因素。固定化被认为是配体配位和包封相结合的结果。四脯氨酸二钠催化剂Rh-2(S-DOSP)(4) （1a）、Rh-2(S-TBSP)(4) （1b）和Rh-2(S-biTISP)(2)(2)均有效固定化。所得的非均相配合物是苯基重氮乙酸甲酯和苯乙烯之间不对称环丙化反应的有效催化剂，在优化条件下，它们可以循环5次，对映体选择性几乎没有损失。三相试验研究表明，当催化剂和重氮化合物均固定时，反应速度非常缓慢，但缓慢的速率排除了环丙烷化主要通过释放-捕获机制发生的可能性。
Dirhodium tetracarboxylates are readily immobilized on agitation in the presence of highly crosslinked polystyrene resins with a pyridine attachment. A systematic study demonstrates that the polymer backbone, the linker, the terminal pyridine group, and the catalyst structure all contribute to the efficiency of dirhodium catalyst immobilization. The immobilization is considered to be due to the combination of ligand coordination and encapsulation. The dirhodium tetraprolinate catalysts, Rh-2(S-DOSP)(4) (1a), Rh-2(S-TBSP)(4) (1b), and Rh-2(S-biTISP)(2) (2), are all efficiently immobilized. The resulting heterogeneous complexes are very effective catalysts for asymmetric cyclopropanation between methyl phenyldiazoacetate and styrene, and under optimized conditions they can be recycled five times with virtually no loss in enantioselectivity. The three-phase test studies indicated that a very slow reaction occurs when both the catalyst and the diazo compound were immobilized, but the slow rate precluded the likelihood that the cyclopropanation was predominately occurring by a release-and-capture mechanism.