Synthesis and characterization of stable iron(IV), tin(IV) and ruthenium(IV) thiatrane complexes

Abstract

Iron(IV) is proposed to be a key oxidation state in many metalloenzymes that catalyze the selective oxidation of hydrocarbons and related compounds using oxygen. This work reports the designed synthesis of stable, diamagnetic, trigonal bipyramidai, iron(IV) thiatrane complexes starting from either iron(II) or iron(III). For example, the reaction of the tris-thiolate ligand, P(C ₆H₃-3-SiMe₃-2-S)₃, (PS₃) ^TMS, (generated in situ from the H₃PS₃ ^TMS proligand and Et₃N) with FeCl₂ under a nitrogen atmosphere produced an emerald green solution which contained [Fe^II (PS₃)^TMS]⁻. Laboratory workup of this compound produced an intensely purpled-colored complex, ClFe ^IV(PS₃)^TMS, which was the first diamagnetic iron(IV) complex and the first trigonal bipyramidal, iron(IV) thiatrane complex to be structurally characterized.

Utilizing this general procedure and a variety of tris-thiolate ligands, this dissertation focuses on the synthesis of complexes of the type XM ^IV(PS₃). Eight additional iron(IV) and the isostructural tin(IV) and ruthenium(IV) complexes with formulas XFe(PS₃) ^TMS where (PS₃)^TMS = P(C₆H ₃-3-Me₃Si-2-S)₃ and X = Br, I, CN, PhSn(PS₃)^TMS, PhSn(PS₃)^Me where (PS₃)^Me = P(C₆H₃-5-Me-2-S) ₃, PhSn(PS₃) where (PS₃) = P(C₆H ₄-2-S)₃, ClRu(PS₃)^TMS and ClRu(PS ₃) have been synthesized. The mechanistic details for the formation of these stable complexes, the identification of metal and nonmetal-containing reaction coproducts and physical and chemical properties of these substances have been pursued.

Five of these complexes, BrFe(PS₃)^TMS, IFe(PS ₃)^TMS, PhSn(PS₃)^TMS, PhSn(PS ₃)^Me and PhSn(PS₃) have been studied crystallographically. PhSn(PS₃)^TMS can be easily converted to either ClFe(PS ₃)^TMS or ClRu(PS₃)^TMS via transmetalation reactions using FeCl₃, FeCl₂, (Et₄N) ₂[Fe₂OCl₆] and RuCl₂(DMSO)₄. These reactions gave insight into the lability of the fifth coordination site (halogen, cyanide or phenyl) in the trigonal bipyramidal complexes as well as the reactivity of the metal centers. The chemical reactivity of CIFe(PS ₃)^TMS has been explored by using this iron(IV) complex as a reagent in the attempted formation of six-coordinate (Et₂NCS ₂)Fe(PS₃)^TMS.

Developing this chemistry and characterizing the resulting complexes provided the foundation needed to prepare a new group of functional and structural models for a wide range of metalloenzymes.