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.