Iron Complexes Derived from {nacnac-(CH2py)2}- and {nacnac-(CH2py)(CHpy)}n Ligands: Stabilization of Iron(II) via Redox Noninnocence

Nacnac-based tetradentate chelates, {nacnac-(CH(2)py)(2)} ({nn(PM)(2)}(-)) and {nacnac-(CH(2)py)(CHpy)}(n) ann(PM)(PI)}(n)) have been investigated in iron complexes. Treatment of Fe{N(TMS)(2)}(2)(THF) with {nn(PM)(2)}H afforded {nn(PM)(2)}FeN(TMS)(2) [1-N(TMS)(2)], which led to {nn(PM)(2)}FeCl (1-Cl) from HCl and to {nn(PM)(2)}FeN3 (1-N-3) upon salt metathesis. Dehydroamination of 1-N(TMS)(2) was induced by L (L = PMe3, CO) to afford {nn(PM)(PI)}Fe(PMe3)(2) [2-(PMe3)(2)] and {nn(PM)(PI)}FeCO (3-CO). Substitution of 2-(PMe3)(2) led to {nn(PM)(PI)}Fe(PMe3)CO [2-(PMe3)CO], and exposure to a vacuum provided {nn(PM)(PI)}Fe(PMe3) (3-PMe3). Metathesis routes to {nn(PM)(PI)}FeL2 (2-L-2; L = PMe3, PMe2Ph) and {nn(PM)(PI)}FeL (3-L; L = PMePh2, PPh3) from [inn(PM)(PI)}(2-)]Li-2 and FeBr2(THF)(2) in the presence of L proved feasible, and 1e(-) and 2e(-) oxidation of 2-(PMe3)(2) afforded 2(+)-(PMe3)(2) and 2(2+)-(PMe3)(2) salts. Mossbauer spectroscopy, structural studies, and calculational assessments revealed the dominance of iron(II) in both high-spin (1-X) and low-spin (2-L-2 and 3-L) environments, and the redox noninnocence (RNI) of {nn(PM)(PI)}(n) [2-L-2, 3-L, n = 2-; 2(+)-(PMe3)(2), n = 1; 2(2+)-(PMe3)(2), n = 0]. A discussion regarding the utility of RNI in chemical reactivity is proffered.