Studies of Tungsten Alkyl Alkylidyne Compounds and Iron Porphyrin Derivatives

This dissertation focuses on two research projects. The first project examines the reactions of tungsten(VI) alkyl alkylidyne and bis-alkylidene complexes with phosphines and water and the studies of thermodynamics and kinetics of the reactions. These studies have been conducted in part to determine the mechanistic pathway in the formation of novel tungsten(VI) species. The second portion of this dissertation focuses on the spin density and structures of biomimetic Fe(III) porphyrin derivatives using neutron and X-ray diffraction techniques. The spin density and magnetic properties of an Fe(III) porphyrin derivative has been determined by polarized neutron diffraction.

In the first portion of this dissertation, reaction of tungsten(VI) alkyl alkylidyne W(CH₂SiMe₃)₃(≡CSiMe3) with Me₂PCH₂CH₂PMe₂ (DMPE), a bidentate phosphine, has been studied (Chapter 2). The reaction gives a DMPEalkylidyne adduct, which subsequently undergoes a tautomerization. The tautomeric mixture then converts to an alkyl alkylidene alkylidyne complex. Thermodynamic and kinetic studies as well as molecular modeling are used to understand these reactions. In Chapter 3, thermodynamic studies have been conducted of the addition of two mono-dentate phosphines to the tungsten(VI) alkyl alkylidyne complex. A reversible reaction has been observed with the mono-dentate phosphines. The reaction of tungsten(VI) alkyl alkylidyne W(CH₂CMe₃)₃(≡CSiMe₃) with H₂O has been pursued. The reaction leads to the observation of the intermediate W₂O₂(µ-O)(CH₂SiMe₃)₂(CH₂CMe₃)₄ and subsequent formation of two oxo trimers. NMR spectroscopic studies have been used to determine the mechanistic pathway in formation of these trimeric complexes.

In the second portion of this dissertation, variable-temperature X-ray studies have been conducted of Fe(TPP)Cl (TPP^2- = meso-tetraphenylporphyrinate) (Chapter 5) and [Fe(TPP)(HIm)₂]Cl (HIm = 1Himidazole) complexes (Chapter 6). The spin-density in the [Fe(TPP)(HIm)₂]Cl (S = 1/2) complex has been probed using polarized neutron diffraction (Chapter 7). The study shows that the spin distribution of the unpaired electron is localized on the Fe(III) center. The Fe(TPP)Cl-d₂₈ and [Fe(TPP)(DIm)₂-d₃₆]Cl complexes have been synthesized and characterized by X-ray diffraction (Chapter 8). A comparison is made between the protonated and per-deuterated X-ray diffraction structures.