Redox-Controlled and Reversible N-N Bond Forming and Splitting with an Iron^IV Terminal Imido Ligand

Oxidation of the low-spin Fe^IV imido complex [{(pyrr)₂py}Fe═NAd] (1) ((pyrr)₂py^2- = 2,6-bis(3,5-di-tert-butyl-pyrrolyl)pyridine, Ad = 1-adamantyl) with AgOAc or AgNO₃ promotes reductive N-N bond coupling of the former imido nitrogen with a pyrrole nitrogen to form the respective ferric hydrazido-like pincer complexes [{(pyrrNAd)(pyrr)py}Fe(κ²-X)] (X = OAc^-, 2; NO₃^-, 2). Reduction of 2 with KC₈ cleaves the N-N bond to reform the Fe^IV imido ligand in 1, whereas acid-mediated demetalation of 2 or 2 yields the free hydrazine ligand [(pyrrNHAd)(pyrrH)py] (3), the latter of which can be used as a direct entry to the iron imido complex when treated with [Fe{N(SiMe₃)₂}₂]. In addition to characterizing these Fe systems, we show how this nitrene transfer strategy can be expanded to Co for the one-step synthesis of Co{(pyrr)(pyrr)py}] (4) ((pyrr)(pyrr)py^2- = 2-(3-tBu-5-(1-adamantylmethyl-2-methylpropane-2-yl)-pyrrol-2-yl)-6-(3,5-tBu₂-pyrrol-2-yl)-pyridine).