Synthesis and Characterization of Iron Complexes with Monoanionic and Dianionic <i>N,N‘,N‘ ‘</i>-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{(iPrN)2C(HNiPr)}2 (1), [Fe{μ-(iPrN)2C(HNiPr)}{(iPrN)2C(HNiPr)}]2 (2), and [Fe{μ-(CyN)2C(HNCy)}{(CyN)2C(HNCy)}]2 (3) were prepared from the reaction of the appropriate lithium tri(alkyl)guanidinate and FeCl3 or FeBr2. The complex [FeBr{μ-(CyN)2C(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 Li2[Fe{μ-(iPrN)2CNiPr}{(iPrN)2C(HNiPr)}]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 Li4(THF)2[Fe{(iPrN)2CNiPr}(CH2SiMe3)2]2 (7). Both complexes 5 and 7 posssess dianionic guanidinate ligands. The reaction of 2 with 1 equiv of LiCH2SiMe3 generated Fe2{μ-(iPrNCNiPr)2(NiPr)}{(iPrN)2C(HNiPr)}2 (6). Compound 6 has a dianionic biguanidinate ligand derived from the coupling of the two bridging guanidinate ligands of 2.