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Photoimmobilized Ni Clusters Boost Photodehydrogenative Coupling of Amines to Imines via Enhanced Hydrogen Evolution Kinetics
journal contribution
posted on 2020-03-10, 19:59 authored by Yi Huang, Cuibo Liu, Mengyang Li, Huizhi Li, Yongwang Li, Ren Su, Bin ZhangImines are important
precursors for pharmaceutical, agricultural,
and synthetic chemistry. The state-of-art synthesis of imines via
condensation of amines with aldehydes or ketones often uses homogeneous
catalysts and dehydrating agents to promote the elimination of water,
which requires huge manpower input for the late-stage purification
process and is usually environmentally unfriendly. Photocatalytic
synthesis of imines from amines oxidation via the release of hydrogen
(H2) is of great promise due to the mild reaction characteristics;
however, the efficiency of such a reaction lags due to the missing
designed photocatalyst owing to the ambiguous reaction mechanism.
Here, we demonstrate that by constructing in situ photoimmobilized
Ni clusters on the CdS photocatalyst, the generation of imines is
dramatically improved with the rapid release of molecular H2 under visible light illumination. Mechanistic investigation reveals
that the adsorption of photogenerated hydrogen atoms during the dehydrogenation
of amines is significantly weakened on Ni clusters, thus resulting
in fast C–N coupling kinetics for the generation of imines.
The photocatalyst presents stable performance with high efficiency.
A remarkably apparent quantum efficiency (AQE) of ∼44% is realized
under 420 nm irradiation for the conversion of 4-methoxybenzylamine
within six consecutive runs. Furthermore, a series of primary and
secondary amines bearing different functional groups (i.e., heterocyclic,
aliphatic, N-heterocycles) that are synthetically challenging by the
condensation process can be selectively converted to the corresponding
imines, featuring its application prospect.