Deprotonation, Chloride Abstraction, and Dehydrohalogenation as Synthetic Routes to Bis‐Pyrazolate Pyridyl Iron(II) Complexes

The process of removal of protons and chloride, dehydrohalogenation, from [(H 2 L)FeCl 2 ] is investigated systematically, to understand the reactivity of the implied transient LFe II . Reaction of [(H 2 L)FeCl 2 ] with 2 equiv. of LiN(SiMe 3 ) 2 yields the “‐ate” complex LiClFe 2 L 2 , as its dimer with every iron five‐coordinate in an FeN 4 Cl environment. To avoid Li + cation derived from LiN(SiMe 3 ) 2 , reaction of Na 2 L with FeCl 2 gives a product from addition of water, paramagnetic Na 2 [NaFe(HL)(L)] 2 (LFeO), which reveals Na/pyrazolate Nβ interactions and a five coordinate oxo group in the OFe 3 Na 2 core of this aggregate. Abstraction of chloride in [(H 2 L)FeCl 2 ] with NaBArF 4 in THF gives paramagnetic [(H 2 L)Fe(THF) 3 ] 2+ , which fails to react with CO. Dehydrohalogenation in the presence of Ph 2 PC 2 H 4 PPh 2 , dppe, gives both [LFe(κ 2 ‐dppe)] 2 (µ‐dppe)] and [LFe(κ 2 ‐dppe)(κ 1 ‐dppe)], diamagnetic saturated species, which can be separated by pentane extraction. Dehydrohalogenation in the presence of t BuNC gives diamagnetic [LFe(CN t Bu) 3 ]. This is selectively methylated at both pyrazolate β‐nitrogen atom to give [L Me Fe( t BuNC) 3 ] 2+ which shows rich cyclic voltammetry, and which is reduced, with KC 8 , to diamagnetic [L Me Fe( t BuNC) 2 ]. Structure determination of some of these, together with IR data on isocyanide stretching frequencies, show L 2– to be a stronger donor than L Me . First installing triflate (to avoid the more persistent chloride ligand) facilitates access to [LFe(Lewis base) 3 ] 2+ complexes, but this cation still shows relatively weak binding of CO to LFe II , which implicates weak π basicity of that d 6 species. Production of paramagnetic bis ‐pincer complexes [(H 2 L) 2 Fe] 2+ and [(L Me ) 2 Fe] 2+ in the presence of abundant Lewis base in polar medium is demonstrated, which illustrates a pincer ligand redistribution challenge to be kept in mind when trying to maintain a 1:1 Fe:pincer ratio, for highest reactivity.