Synthesis and Reactivity of an Isolable Cobalt(I) Complex Containing a β-Diketiminate-Based Acyclic Tetradentate Ligand

A model for cobalamin was synthesized using a new monoanionic tetradentate nitrogen donor ligand; 2-(4-tolyl)-1,3-bis­(2-isopropylpyridyl)­propenediimine (Tol-BDI(2‑pp)2H) (1), which utilizes isopropylpyridines as pendant arms on a β-diketiminate (BDI) backbone. During the synthesis of 1, the rearrangement product, Tol-BDI(2‑pp)(4‑pp)H (2) was observed. Metalation of 1 with zinc iodide and cobalt chloride yielded the corresponding Tol-BDI(2‑pp)2ZnI (3) and Tol-BDI(2‑pp)2CoCl (4) complexes. The redox properties of 4 in comparison to cobalamin were examined through electrochemical studies. Electrochemical and bulk reduction of complex 4 gave a diamagnetic cobalt­(I) complex, Tol-BDI(2‑pp)2Co (5). Reactivity of 5 toward C-X bonds was investigated using methyl iodide and 1-iodo-2-(trimethylsilyl)­acetylene, yielding Tol-BDI(2‑pp)2Co­(CH3)I and Tol-BDI(2‑pp)2Co­(C2Si­(CH3)3)I respectively. Synthesis and characterization details for these complexes, including the crystal structure of 3, are reported.