Unlocking Heterobimetallic Architectures in a Symmetric PNNP Ligand Environment

Bimetallic cooperation is a defining feature of many enzymatic and synthetic catalytic systems, where short metal-metal separations enable cooperative substrate activation. Synthesis of complexes wherein two distinct metal centers are placed in close proximity is challenging and typically requires the use of nonsymmetric ligand environments. Here, we report the synthesis, structural characterization, and electronic analysis of heterobimetallic complexes supported by a symmetric PNNP ligand. A mononuclear Ru(II) complex serves as a modular platform for the stepwise construction of RuRu, ZnRu, and CoRu assemblies. The resulting heterobimetallic ZnRu and CoRu complexes adopt closely related architectures. Upon deprotonation, ligand dearomatization induces a pronounced contraction of the metal-metal distance, underscoring the unique ability of the PNNP scaffold to geometrically tune bimetallic cores. Density Functional Theory (DFT) combined with Quantum Theory of Atoms in Molecules (QTAIM) analysis reveals that the CoRu complex features a metallophilic interaction between the two metal centers, whereas the ZnRu analogue lacks such an interaction. Taken together, this study demonstrates that the symmetric PNNP ligand is a versatile platform for assembling heterobimetallic complexes and that controlled ligand deprotonation offers a straightforward route to modulate metal-metal separations and electronic communication within these systems.