期刊
ORGANOMETALLICS
卷 38, 期 7, 页码 1468-1478出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.organomet.8b00888
关键词
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资金
- National Science Foundation [CHE-1464734, CHE-1800151]
- NSF-MRI grant [CHE-1625737, CHE-1726092]
- U.S. Department of Energy, Office of Basic Energy Sciences [DE-AC02-05CH11231]
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.
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