Hydrogen‐Bond‐Mediated Formation of C‐N or C=N Bond during Photocatalytic Reductive Coupling Reaction over CdS Nanosheets

Abstract Reductive amination of carbonyl compounds and nitro compounds represents a straightforward way to attain imines or secondary amines, but it is difficult to control the product selectivity. Herein, we report the selective formation of C−N or C=N bond readily manipulated through a solvent‐induced hydrogen bond bridge, facilitating the swift photocatalytic reductive coupling process. The reductive‐coupling of nitro compounds with carbonyl compounds using formic acid and sodium formate as the hydrogen donors over CdS nanosheets selectively generates imines with C=N bonds in acetonitrile solvent; while taking methanol as solvent, the C=N bonds are readily hydrogenated to the C−N bonds via hydrogen‐bonding activation. Experimental and theoretical study reveals that the building of the hydrogen‐bond bridge between the hydroxyl groups in methanol and the N atoms of the C=N motifs in imines facilitates the transfer of hydrogen atoms from CdS surface to the N atoms in imines upon illumination, resulting in the rapid hydrogenation of the C=N bonds to give rise to the secondary amines with C−N bonds. Our method provides a simple way to control product selectivity by altering the solvents in photocatalytic organic transformations.