A structurally unique class of hydrocarbon-soluble, ancillary-ligand-free, tetrametallic Co(I) and Ni(I) clusters is reported. The highly unsaturated complexes are supported by simple, sterically bulky phosphoranimide ligands, one per metal. The electron-rich nitrogen centers are strongly bridging but sterically limited to bimetallic interactions. The hydrocarbon-soluble clusters consist of four coplanar metal centers, mutually bridged by single nitrogen atoms. Each metal center is monovalent, rigorously linear, and two-coordinate. The clusters are in essence two-dimensional atomic-scale "molecular squares," a structural motif adapted from supramolecular chemistry. Both clusters exhibit high solution-phase magnetic susceptibility at room temperature, suggesting the potential for applications in molecular electronics. Designed to be catalyst precursors, both clusters exhibit high activity for catalytic hydrogenation of unsaturated hydrocarbons at low pressure and temperature.