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) (<b>1</b>), which utilizes isopropylpyridines as pendant arms on a β-diketiminate (BDI) backbone. During the synthesis of <b>1</b>, the rearrangement product, Tol-BDI^{(2‑pp)(4‑pp)}H (<b>2</b>) was observed. Metalation of <b>1</b> with zinc iodide and cobalt chloride yielded the corresponding Tol-BDI^(2‑pp)2ZnI (<b>3</b>) and Tol-BDI^(2‑pp)2CoCl (<b>4</b>) complexes. The redox properties of <b>4</b> in comparison to cobalamin were examined through electrochemical studies. Electrochemical and bulk reduction of complex <b>4</b> gave a diamagnetic cobalt­(I) complex, Tol-BDI^(2‑pp)2Co (<b>5</b>). Reactivity of <b>5</b> 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 <b>3</b>, are reported