Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 23, Issue 32, Pages 7761-7771Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201700816
Keywords
amides; cooperative effects; hemilability; metal catalysis; water activation
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Funding
- Department of Science and Technology (DST) of India
- Department of Atomic Energy (DAE)
- Council of Scientific and Industrial Research (CSIR)
- DAE India
- UGC India
- CSIR India
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The Ni-II complex 1 containing pyridyl- and hydroxy-functionalized N-heterocyclic carbenes (NHCs) is synthesized and its catalytic utility for the selective nitrile hydration to the corresponding amide under base-free conditions is evaluated. The title compound exploits a hemilabile pyridyl unit to interact with a catalytically relevant water molecule through hydrogen-bonding and promotes a nucleophilic water attack to the nitrile. A wide variety of nitriles is hydrated to the corresponding amides including the pharmaceutical drugs rufinamide, Rifater, and piracetam. Synthetically challenging alpha-hydroxyamides are accessed from cyanohydrins under neutral conditions. Related catalysts that lack the pyridyl unit (i.e., compounds 2 and 4) are not active whereas those containing both the pyridyl and the hydroxy or only the pyridyl pendant (i.e., compounds 1 and 3) show substantial activity. The linkage isomer 1' where the hydroxy group is bound to the metal instead of the pyridyl group was isolated under different crystallization conditions insinuating a ligand hemilabile behavior. Additional pK(a) measurements reveal an accessible pyridyl unit under the catalytic conditions. Kinetic studies support a ligand-promoted nucleophilic water addition to a metal-bound nitrile group. This work reports a Ni-based catalyst that exhibits functional hemilability for hydration chemistry.
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