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

Abstract

Iron(II) dialkyl compounds [FeR 2 ] (R = C(SiMe 3 ) 2 C 5 H 4 N-2 ( 1 ), C(Ph)(SiMe 3 )C 5 H 4 N-2 ( 2 ), CH(SiMe 3 )C 9 H 6 N-8 ( 4 )) and [{Fe(CHSi t BuMe 2 C 5 H 4 N-2) 2 } 2 ] ( 3 ) have been prepared from the reaction of FeCl 2 with the appropriate N-functionalized alkyllithium reagent in a 1:2 molar ratio. The monoalkylated iron(II) complex [Fe{CPhSiMe 3 C 5 H 4 N-2}(Cl)(TMEDA)] ( 5 ) has been prepared by treating FeCl 2 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 d 6 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 Me OH (Ar Me = 2,6- t Bu 2 -4-MeC 6 H 2 ) and ArSH (Ar = 2,4,6- t Bu 3 C 6 H 2 ) gave the neutral monomeric iron(II) bis(aryloxide) [Fe(OAr Me ) 2 {CH(SiMe 3 ) 2 C 5 H 4 N-2}] ( 6 ) and dithiolate [Fe(SAr) 2 {CH(SiMe 3 ) 2 C 5 H 4 N-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.