Synthesis and Reactivity of NHC-Stabilized Iron(II)-Mesityl Complexes

We present the synthesis of a series of NHC-stabilized iron(II) complexes of the type [Fe(NHC)(2)Mes(2)] and [Fe(NHC)Mes(2)], starting from [Fe(2)Mes(4)] and the NHC. Depending on the steric demand of the NHC used, tetrahedral {[Fe(Me(2)Im)(2)Mes(2)] 1 and [Fe(MeiPrIm)(2)Mes(2)](2)}, square-planar {trans-[Fe(iPr(2)Im)(2)Mes(2)](3)}, or trigonal-planar {[Fe(R(2)Im)Mes(2)]; R = tBu 6, Dipp 7, Dipp(2)H(2) 8} complexes were isolated. Three-coordinate complexes [Fe(R(2)Im)Mes(2)] (R = Me 4, iPr 5) of smaller carbenes were synthesized via ligand exchange of [Fe(NHC)(2)-Mes(2)] and [Fe(2)Mes(4)]. The reactivity of trans-[Fe(iPr(2)Im)(2)Mes(2)] 3 towards small molecules and element-hydrogen compounds was investigated. The reaction of 3 and 2 with dioxygen led to the tetrameric-cluster complexes [{Fe(R(2)Im)(OMes)(mu 2-O)} 4] 9 and 10 (R = iPr 9, Me 10). The reaction of 3 with CO afforded [Fe(iPr2Im) 2(CO) 3] 11. Reactions of 3 with E-H compounds (E = O, S, N, P, Sn), with substitution of the mesityl ligands, produced the complexes [Fe(iPr(2)Im)(2)(OtBu)(2)] 12, [Fe(iPr(2)Im)(2)(OPh)(2)] 13, [Fe(iPr(2)Im)(2)(SPh)(2)] 14, [Fe(iPr(2)Im)(2)(NHPh)(2)] 15, cis-[Fe(iPr(2)Im) 2{oC(6)H(4)(NH)(2)}] 16, [Fe(iPr(2)Im)(2)(PHPh) 2] 17, [Fe(iPr(2)Im)(2)(PPh2)(2)] 18, trans-[Fe(Me(2)Im)(2)(SnnBu(3))(2)] 19, and trans-[Fe(iPr(2)Im)(2)(SnnBu(3))(2)] 20. The complexes 16, 17, 19, and 20 adopt square-planar structures. The reaction of 3 with phenylsilane afforded crystallographically characterized [Fe(iPr(2)Im)(2)(mu 2-H)(3)(SiPh2H){SiH2(iPr(2)Im)}] 21.