Dehydrogenative Coupling of Aldehydes with Alcohols Catalyzed by a Nickel Hydride Complex
Dehydrogenative Coupling of Aldehydes with Alcohols Catalyzed by a Nickel Hydride Complex
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DOI：
10.1021/acs.organomet.8b00888
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发表时间：
2019-04-08
期刊：
影响因子：
2.8
通讯作者：
Guan, Hairong
中科院分区：
文献类型：
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作者：
Eberhardt, Nathan A.;Wellala, Nadeesha P. N.;Guan, Hairong
镍氢化物配合物{2,6-((Pr2PO)- pr -i)(2)C6H3}NiH催化RCHO和R‘ oh的偶联生成RCO2R’和RCH2OH，其中醛也作为氢受体，醇也作为溶剂。该催化体系耐受的官能团包括CF3、NO2、Cl、Br、NHCOMe和NMe2，而含酚化合物不是可行的底物或溶剂。脱氢偶联反应可由空气稳定的氯化镍配合物{2,6-((Pr2PO)- pr -i)(2)C6H3}NiCl与NaOMe联合催化。未纯化的醛中的酸与氢化物反应形成羧酸镍配合物，其催化活性不高。如果水大量存在，则会形成{2,6-((Pr2PO)- pr -i)(2)C6H3}NiOH，从而降低催化效率，而{2,6-((Pr2PO)- pr -i)(2)C6H3}NiOH是由{2,6-((Pr2PO)- pr -i)(2)C6H3}NiCl和NaOH原位生成的{2,6-((Pr2PO)- pr -i)(2)C6H3}NiOH可以转化为醇氧化合物，成为具有催化能力的物质。提出的催化机理是醛插入到氢化镍和醇化镍中间体中，这两种机制都已被实验观察到。分别合成了{2,6-((Pr2PO)- pr -i)(2)C6H3}- nioc (O)Ph、{2,6-((Pr2PO)- pr -i)(2)C6H3}NiOPh和{2,6-((Pr2PO)- pr -i)(2)C6H3}NiOPh中心点HOPh，并进行了晶体学表征和催化反应测试。虽然含酚分子不能作为底物或溶剂，但{2,6-((Pr2PO)- pr -i)(2)C6H3}NiOPh和{2,6-((Pr2PO)- pr -i)(2)C6H3}NiOPh中心点HOPh都能有效催化PhCHO与EtOH的脱氢偶联。
A nickel hydride complex, {2,6-((Pr2PO)-Pr-i)(2)C6H3}NiH, has been shown to catalyze the coupling of RCHO and R'OH to yield RCO2R' and RCH2OH, where the aldehyde also acts as a hydrogen acceptor and the alcohol also serves as the solvent. Functional groups tolerated by this catalytic system include CF3, NO2, Cl, Br, NHCOMe, and NMe2, whereas phenol-containing compounds are not viable substrates or solvents. The dehydrogenative coupling reaction can alternatively be catalyzed by an air-stable nickel chloride complex, {2,6-((Pr2PO)-Pr-i)(2)C6H3}NiCl, in conjunction with NaOMe. Acids in unpurified aldehydes react with the hydride to form nickel carboxylate complexes, which are catalytically inactive. Water, if present in a significant quantity, decreases the catalytic efficiency by forming {2,6-((Pr2PO)-Pr-i)(2)C6H3}NiOH, a drying agent, {2,6-((Pr2PO)-Pr-i)(2)C6H3}NiOH generated in situ from {2,6- ((Pr2PO)-Pr-i)(2)C6H3}NiCl and NaOH can be converted to an alkoxide species, becoming catalytically competent. The proposed catalytic mechanism features aldehyde insertion into the nickel hydride as well as into a nickel alkoxide intermediate, both of which have been experimentally observed. Several mechanistically relevant nickel species including {2,6-((Pr2PO)-Pr-i)(2)C6H3}-NiOC(O)Ph, {2,6-((Pr2PO)-Pr-i)(2)C6H3}NiOPh, and {2,6-((Pr2PO)-Pr-i)(2)C6H3}NiOPh center dot HOPh have been independently synthesized, crystallographically characterized, and tested for the catalytic reaction. While phenol-containing molecules cannot be used as substrates or solvents, both {2,6-((Pr2PO)-Pr-i)(2)C6H3}NiOPh and {2,6-((Pr2PO)-Pr-i)(2)C6H3}NiOPh center dot HOPh are efficient in catalyzing the dehydrogenative coupling of PhCHO with EtOH.