Synthesis and characterization of iron complexes with monoanionic and dianionic N,N′,N"-trialkylguanidinate ligands

Trisubstitued N,N',N"-tri(alkyl)guanidinate anions have been used in the synthesis of a family of Fe(II) and Fe(III) complexes. Complexes FeCl{((PrN)-Pr-i)(2)C((HNPr)-Pr-i)}(2) (1), [Fe{mu-((PrN)-Pr-i)(2)C((HNPr)-Pr-i)}{((PrN)-Pr-i)(2)C((HNPr)-Pr-i)}](2) (2), and [Fe{mu-(CyN)(2)C(HNCy)}{(CyN)(2)C(HNCy)}](2) (3) were prepared from the reaction of the appropriate lithium tri(alkyl)guanidinate and FeCl3 or FeBr2. The complex [FeBr{mu-(CyN)(2)C(HNCy)}](2) (4), an apparent intermediate in the formation of 3, has also been isolated and characterized. Complexes 1 and 2 react with alkyllithium reagents to yield products that depend on the identity of the reagent as well as the reaction stoichiometry. Reaction of 2 with MeLi (1:2 ratio) produces Li-2[Fe{mu-((PrN)-Pr-i)(2)C=(NPr)-Pr-i}{((PrN)-Pr-i)(2)C((HNPr)-Pr-i)}](2) (5). Reaction of 1 with an equimolar amount of LiCH2SiMe3 results in reduction to Fe(II) and generation of 2 while reaction with 4 LiCH2SiMe3 proceeds by a combination of reduction, substitution, and deprotonation of guandinate to yield Li-4(THF)(2)[Fe{((PrN)-Pr-i)(2)(CNPr)-Pr-i}(CH2SiMe3)(2)](2) (7). Both complexes 5 and 7 posssess dianionic guanidinate ligands. The reaction of 2 with 1 equiv of LiCH2SiMe3 generated Fe-2{mu-((PrNCNPr)-Pr-i-Pr-i)(2)((NPr)-Pr-i)}{((PrN)-Pr-i)(2)C((HNPr)-Pr-i)}(2) (6). Compound 6 has a dianionic biguanidinate ligand derived from the coupling of the two bridging guanidinate ligands of 2.