Bis(dialkylphosphino)ferrocene-Ligated Nickel(II) Precatalysts for Suzuki-Miyaura Reactions of Aryl Carbonates
Bis(dialkylphosphino)ferrocene-Ligated Nickel(II) Precatalysts for Suzuki-Miyaura Reactions of Aryl Carbonates
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DOI：
10.1021/acs.organomet.9b00543
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发表时间：
2019-09-08
期刊：
影响因子：
2.8
通讯作者：
Peczak, Ian L.
中科院分区：
文献类型：
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作者：
Barth, Emily L.;Davis, Ryan M.;Peczak, Ian L.
羰基碳酸酯是合成有机化学中一种常见的保护基团，在交叉偶联反应中具有潜在的亲电价值。在此，在对不同的预催化剂进行了全面的评估后，我们证明（dcypf）Ni（2-乙基苯基）（Br） （dcypf = 1,1-二-（双环己基磷酸）二茂铁）是一种高效的以各种芳基碳酸酯为底物的Suzuki-Miyaura反应预催化剂。机理研究表明，（dypf）Ni（2-乙基苯基）（Br）是这些反应的有效预催化剂，它含有双齿膦，以反式结构结合，有两个原因：(i)它迅速形成Ni(0)活性物质；（ii）它最大限度地减少Ni(0)活性物质与未活化的Ni（ii）预催化剂和循环中的Ni（ii）配合物之间的比例反应，形成催化活性的Ni(i)物质。相比之下，目前的预催化剂（dppf）Ni(o- toyl)(Cl) （dppf = 1,1-二（二苯基膦）二茂铁），含有双齿膦，以顺式结构结合，在活化过程中形成Ni(I)物种，并且对芳基碳酸盐偶联基本上没有活性。尽管在分子水平上，dypf体系比dppf体系更活跃的确切原因尚不清楚，但我们的研究结果表明，一般来说，dypf配体支持的Ni催化剂在涉及相对缓慢氧化加成的底物（如碳酸芳基）的催化反应中表现更好。
Aryl carbonates, a common protecting group in synthetic organic chemistry, are potentially valuable electrophiles in cross-coupling reactions. Here, after performing a thorough evaluation of different precatalysts, we demonstrate that (dcypf)Ni(2-ethylphenyl)(Br) (dcypf = 1,1-bis-(dicyclohexylphosphino)ferrocene) is an efficient precatalyst for Suzuki-Miyaura reactions using a variety of aryl carbonates as substrates. Mechanistic studies indicate that (dcypf)Ni(2-ethylphenyl)(Br), which contains a bidentate phosphine that binds in a trans geometry, is an effective precatalyst for these reactions for two reasons: (i) it rapidly forms the Ni(0) active species and (ii) it minimizes comproportionation reactions between the Ni(0) active species and both the unactivated Ni(II) precatalyst and on-cycle Ni(II) complexes to form catalytically inactive Ni(I) species. In contrast, the state of the art precatalyst (dppf)Ni(o-tolyl)(Cl) (dppf = 1,1-bis(diphenylphosphino)ferrocene), which contains a bidentate phosphine that binds in a cis geometry, forms Ni(I) species during activation and is essentially inactive for aryl carbonate couplings. Although the exact reasons on a molecular level why the dcypf system is more active than the dppf system are unclear, our results indicate that in general Ni catalysts supported by the dcypf ligand will give better performance for catalytic reactions involving substrates which undergo relatively slow oxidative addition, such as aryl carbonates.