Sterically Encumbered Iron(II) Thiolate Complexes: Synthesis and Structure of Trigonal Planar [Fe(SR)3]- (R = 2,4,6-t-Bu3C6H2) and Moessbauer Spectra of Two- and Three-Coordinate Complexes (original) (raw)

1995, Inorganic Chemistry

The synthesis and structural characterization of three compounds containing three-coordinate Fe(II) and stabilized by sterically encumbered thiolate ligands are reported. Reaction of [Fez(SC6H2-2,4,6-t-B~3)4] (3) with LiSC6H2-2,4,6-t-Bu3 in ether/THF/hexane afforded [Li(THF)2(5)]9SC&14 (5 = [Fe(SC6H2-2,4,6-t-Bu3)3]-). Addition of PbPC1 to a reaction mixture in toluene followed by recrystallization of the product from acetonitrile yielded (PhP)[5]*2MeCNC7H8. The compound [Fe3(SCsH2-2,4,6-i-P3)4(N(siMe3)2)2] was prepared by the reaction of [Fe(N(SiMe3)2)2] (6) with the thiol in toluene. [ L~( T H F )~(~) ] -O .~C~H I~ crystallizes in monoclinic space group P21/c with a = 9.809(2) A, b = 22.507(5) A, c = 29.553(5) A, p = 95.72(2)", and Z = 4 (130 K). (PhP)-[5]*2MeCNC,H8 was obtained in monoclinic space group P21 with a = 17.538(5) A, b = 14.912(4) A, c = 17.608(5) A, p = 115.71(3)', and Z = 2 (143 K). These compounds contain the first example of mononuclear Fe(I1) in a close approach to a trigonal planar [5] or a distorted trigonal planar [Li(THF)2(5)] sulfur coordination environment. In the P b P salt, [5] exhibits the mean values Fe-S = 2.274(9) A and S-Fe-S = 120(3)", while in [Li(THF)2(5)] the Li+ ion bridges two sulfur atoms, causing a lengthening (0.06-0.07 A) of the Fe-S bridged bond lengths and constriction of the bridged S-Fe-S angle (92.2(1)"). Compound 6 crystallizes in P21/c with a = 14.521(5) A, b = 41.60(2) A, c = 14.241(4) A, p = 100.42(2)', and Z = 4 (130 K). The structure has a linear Fe3@2-SR)4 fragment with an almost linear Fe3 array involving the central Fe(I1) atom in a severely distorted tetrahedral environment; the terminal Fe(I1) atoms are three-coordinate and planar with terminal N(SiMe3)z ligands. Complex 5 expands the family of homoleptic molecular Fe(I1) thiolates to five structural types; complexes 5 and 6 with two previously reported species of the type [Fe2(SR)4] constitute the known examples of three-coordinate Fe" with partial or complete sulfur ligation. The zero-field Mossbauer spectra of examples of the five types of homoleptic Fe(II) thiolates are reported together with several tetrahedral complexes having Fe"-S/SR coordination in order to determine what structural distinctions could be made from isomer shifts and quadrupole splittings.