Synthesis and Structures of Iron(II) Alkyl and Thiolate Compounds Containing Sterically Hindered N-Functionalized Alkyl Ligands

Iron(II) dialkyl compounds [FeR₂] (R = C(SiMe₃)₂C₅H₄N-2 (1), C(Ph)(SiMe₃)C₅H₄N-2 (2), CH(SiMe₃)C₉H₆N-8 (4)) and [{Fe(CHSi^tBuMe₂C₅H₄N-2)₂}₂] (3) have been prepared from the reaction of FeCl₂ with the appropriate N-functionalized alkyllithium reagent in a 1:2 molar ratio. The monoalkylated iron(II) complex [Fe{CPhSiMe₃C₅H₄N-2}(Cl)(TMEDA)] (5) has been prepared by treating FeCl₂ with a stoichiometric amount of the organolithium reagent. X-ray analysis revealed that the alkyl ligands are bonded to the metal centers in a chelating manner in the mononuclear compounds 1 and 5, whereas in 3 one of the alkyl ligands forms an interligand bridge betwen the two iron centers. Compounds 1, 2, 4, and 5 have magnetic moments in the range 4.24−4.96 μ_B that are characteristic of a high-spin d⁶ electronic configuration with four unpaired electrons. The magnetic moment of the binuclear compound 3 is 2.92 μ_B per iron atom, apparently a consequence of antiferromagnetic coupling between the two metal centers. Subsequent reaction of 1 with Ar^MeOH (Ar^Me = 2,6-^tBu₂-4-MeC₆H₂) and ArSH (Ar = 2,4,6-^tBu₃C₆H₂) gave the neutral monomeric iron(II) bis(aryloxide) [Fe(OAr^Me)₂{CH(SiMe₃)₂C₅H₄N-2}] (6) and dithiolate [Fe(SAr)₂{CH(SiMe₃)₂C₅H₄N-2}] (7), respectively. Both of the latter compounds have a rare coordination number of 3 at the iron(II) center. The magnetic moment of 5.11 μ_B for 7 indicates a high-spin configuration with four unpaired electrons on the iron(II) center. Electrochemical studies on the compoounds are also reported.