To study the coordination chemistry and reactivity of dinuclear complexes, our group has developed the PNNP expanded pincer ligand system. This naphthyridine based ligand can tightly bind two metal atoms in close proximity, which allows for potential MMC in well-defined dinuclear complexes. Previously, this ligand has been used to make copper , iron and ruthenium complexes (Scheme 1). Motivated by our interest to further explore the potential of the PNNP ligand with other 1 st row transition metals, especially those that readily adopt high spin-states, we here report the coordination chemistry of the PNNP ligand with cobalt. We disclose the synthesis and reactivity of two high-spin dinuclear cobalt(II) complexes and investigate their reactivity with silanes. In addition, two low-spin dinuclear cobalt complexes featuring unusual bridging Si-based ligands are investigated.