Well-Defined syn Multimetallic Complexes Supported by a Geometrically Flexible Tetraamidodiamine Ligand

Multimetallic complexes are an excellent platform to study the effects of metal-metal cooperativity on reactivity. Herein, we describe the coordination chemistry of a highly flexible tetraamidodiamine (tada) scaffold with nearly all of the first-row transition metals from V to Zn, forming multimetallic complexes that were characterized primarily by NMR spectroscopy and X-ray diffraction studies. For most of the metals, the resulting tada complexes adopt a syn-closed bimetallic binding geometry with close metal-metal contacts. In the case of Zn, a tetrametallic intermediate with an anti-tada geometry was observed to precede the formation of the syn-closed bimetallic product. In contrast, Cu was found to form a tetrametallic syn-open complex. Overall, this work demonstrates the significant flexibility of the tada ligand scaffold, as it can easily adopt multiple different binding geometries with metal-metal distances that span nearly 5 Å.