STERICALLY ENCUMBERED IRON(II) THIOLATE COMPLEXES - SYNTHESIS AND STRUCTURE OF TRIGONAL PLANAR [FE(SR)3](-) (R=2,4,6-T-BU(3)C(6)H(2)) AND MOSSBAUER-SPECTRA OF 2-COORDINATE AND 3-COORDINATE COMPLEXES

The synthesis and structural characterization of three compounds containing three-coordinate Fe(II) and stabilized by sterically encumbered thiolate ligands are reported. Reaction of [Fe-2(SC6H2-2,4,6-t-Bu(3))(4)] (3) with LiSC6H2-2,4,6-t-Bu(3) in ether/THF/hexane afforded [Li(THF)(2)(5)]0.5C(6)H(14) (5 = [Fe(SC6H2-2,4,6-t-Bu(3))(3)](-)). Addition of Ph(4)PCl to a reaction mixture in toluene followed by recrystallization of the product from acetonitrile yielded (Ph(4)P)[5]. 2MeCN . C7H8. The compound [Fe-3(SC6H2-2,4,6-i-Pr-3)(4)(N(SiMe(3))(2))(2)] was prepared by the reaction of [Fe(N(SiMe(3))(2))(2)] (6) with the thiol in toluene. [Li(THF)(2)(5)]. 0.5C(6)H(14) crystallizes in monoclinic space group P2(1)/c with a = 9.809(2) Angstrom, b = 22.507(5) Angstrom, c = 29.553(5) Angstrom, beta = 95.72(2)degrees, and Z = 4 (130 K). (Ph(4)P)-[5]. 2MeCN . C7H8 was obtained in monoclinic space group P2(1) with a = 17.538(5) Angstrom, b = 14.912(4) Angstrom, c = 17.608(5) Angstrom, beta = 115.71(3)degrees, and Z = 2 (143 K). These compounds contain the first example of mononuclear Fe(II) in a close approach to a trigonal planar [5] or a distorted trigonal planar [Li(THF)(2)(5)] sulfur coordination environment. In the Ph(4)P salt, [5] exhibits the mean values Fe-S = 2.274(9) Angstrom and S-Fe-S = 120(3)degrees, while in [Li(THF)(2)(5)] the Li+ ion bridges two sulfur atoms, causing a lengthening (0.06-0.07 Angstrom) of the Fe-S bridged bond lengths and constriction of the bridged S-Fe-S angle (92.2(1)degrees). Compound 6 crystallizes in P2(1)/c with a = 14.521(5) Angstrom, b = 41.60(2) Angstrom, c = 14.241(4) Angstrom, beta = 100.42(2)degrees, and Z = 4 (130 K). The structure has a linear Fe-3(mu(2)-SR)4 fragment with an almost linear Fes array involving the central Fe(II) atom in a severely distorted tetrahedral environment; the terminal Fe(II) atoms are three-coordinate and planar with terminal N(SiMe(3))2 ligands. Complex 5 expands the family of homoleptic molecular Fe(II) thiolates to five structural types; complexes 5 and 6 with two previously reported species of the type [Fe-2(SR)4] constitute the known examples of three-coordinate Fe-II 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-II-S/SR coordination in order to determine what structural distinctions could be made from isomer shifts and quadrupole splittings. From the limited data set, it is tentatively concluded that trigonal planar Fe-II(SR)(3) can be distinguished from tetrahedral Fe-II(SR)(4) and Fe-II-S/SR units on the basis of its smaller quadrupole splitting (0.81 mm/s for 5 at 4.2-100 K).