Are heterogeneous catalysts precursors to homogeneous catalysts?
Are heterogeneous catalysts precursors to homogeneous catalysts?
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DOI：
10.1021/ja016877v
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发表时间：
2001-10-17
影响因子：
15
通讯作者：
Reider, PJ
中科院分区：
文献类型：
--
作者：
Davies, IW;Matty, L;Reider, PJ
均相和非均相催化剂具有各自独特的优点。1多相催化剂的优点是在反应结束时，催化剂可以通过简单的过滤除去。原则上，产物未被过渡金属或配体污染，并且允许催化剂再循环到下一个反应中。[2]虽然均相催化和多相催化之间的区别似乎很明确，但在许多情况下，过渡金属可能会浸出到溶液中。在这些情况下，始终存在的问题是催化活性是否与浸出的金属有关。在其他情况下，尚不清楚是否发生了过渡金属催化剂的“释放和捕获”。我们报告了一个简单的明确的测试，以确定存在的均相催化剂，并证明其在三个原型反应中的应用。这种方法不仅澄清了催化活性物质的相，而且还允许获得关于该系统的附加机械信息。我们最初的研究是由1羰基化得到甲氧羰基环戊烯酮2（当量1）。虽然这种转化用常规的均相催化剂Pd（PPh 3）2Cl 2，3进行得相当好，但为了简化产物分离，寻求用于该反应的非均相催化剂。在我们的许多项目中，催化剂的去向在加工过程中尤为重要，因为在药品中过渡金属残留物的可接受水平受到高度管制。Pd/C已用于许多钯催化反应。4、5通过催化剂的平行筛选，在小规模条件下确定了最佳反应条件。6以1摩尔规模使用这些条件（1摩尔% Pd/C，60 ℃，80 psig CO，1 M DMA，2当量Bu 3 N，5当量MeOH，10小时）导致以98-99%产率形成2。7没有还原、二聚或酰胺形成的痕迹8，质量平衡由两种低水平杂质（参见
Homogeneous and heterogeneous catalysts offer their own distinct advantages. 1 Heterogeneous catalysts have an advantage that at the end of reaction the catalyst can be removed by simple filtration. In principle the product is un-contaminated with a transition metal or ligand and allows the catalyst to be recycled into the next reaction. 2 While the distinction between homogeneous and heterogeneous catalysis seems well-defined, in many cases there may be leaching of the transition metal into solution. In these instances the question that always remains is whether the catalytic activity resides with the leached metal. In other situations, it is unclear whether a “release and capture” of the transition metal catalyst has occurred. We report a simple unambiguous test to determine the presence of a homogeneous catalyst and demonstrate its application in three prototypical reactions. Not only does this method clarify the phase of the catalytically active species it also allows additional mechanistic information to be obtained regarding the system. Our initial studies were prompted by the carbonylation of 1 to give the carbomethoxycyclopentenone 2 (eq 1). Although this transformation worked quite well with the conventional homogeneous catalyst Pd (PPh3) 2Cl2, 3 a heterogeneous catalyst was sought for this reaction to simplify product isolation. In many of our programs, the fate of the catalyst is especially important during processing since the acceptable level of transition metal residuals is highly regulated in pharmaceutical products. Pd/C has been used for a number of palladium-catalyzed reactions. 4, 5 After parallel catalyst screening, the optimal conditions were identified at small scale. 6 Using these conditions at 1 mol scale (1 mol% Pd/C, 60 C, 80 psig CO, 1 M DMA, 2 equiv Bu3N, 5 equiv MeOH, 10 h) led to the formation of 2 in 98-99% yield. 7 There was no trace of reduction, dimerization, or amide formation8 and mass balance was accounted for by two low-level impurities (see