Despite the extensive applications,
selective and diverse access
to N,N′-diarylethane-1,2-diamines remains,
to date, a challenge. Here, by developing a bifunctional cobalt single-atom
catalyst (CoSA-N/NC), we present a general method for direct
synthesis of such compounds via selective reductive coupling of cheap
and abundant nitroarenes and formaldehyde, featuring good substrate
and functionality compatibility, an easily accessible base metal catalyst
with excellent reusability, and high step and atom efficiency. Mechanistic
studies reveal that the N-anchored cobalt single atoms (CoN4) serve as the catalytically active sites for the reduction processes,
the N-doped carbon support enriches the HCHO to timely trap the in situ formed hydroxyamines and affords the requisite nitrones
under weak alkaline conditions, and the subsequent inverse electron
demand 1,3-dipolar cycloaddition of the nitrones and imines followed
by hydrodeoxygenation of the cycloadducts furnishes the products.
In this work, the concept of catalyst-controlled nitroarene reduction
to in situ create specific building blocks is anticipated
to develop more useful chemical transformations.