Access Type

Open Access Dissertation

Date of Award

January 2025

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Chemistry

First Advisor

Stanislav Groysman

Abstract

ABSTRACTTRANSITION METAL ALKOXIDE COMPLEXES SYNTHESIS USING THALLIUM REAGENTS AND DESIGN OF IRON(II)-ALKOXIDE CARBENE COMPLEXES AND THEIR REACTIVITY by LAKSHANI WATHSALA KULATHUNGAGE May 2025 Advisor: Dr. Stanislav Groysman Major: Chemistry (Inorganic) Degree: Doctor of Philosophy

This dissertation focuses on the synthesis and reactivity of transition metal and main group metal alkoxide complexes. The dissertation began with exploring a novel, efficient synthetic route towards transition metal alkoxides involving thallium reagents. A novel dimeric Tl2(OCtBu2Ph)2 complex was synthesized in the reaction between a lithium alkoxide and thallium precursor TlPF6. Tl2(OCtBu2Ph)2 served as a convenient precursor to the formation of old and new transition metal alkoxide complexes (M = Cr, Fe, Cu, Zn), including a rare example of T-shaped Zn(OCtBu2Ph)2(THF) complex, which could not be previously synthesized using conventional synthetic routes. The reaction of [Ru(cymene)Cl2]2 with Tl2(OCtBu2Ph)2 results in the formation of a ruthenium(II) alkoxide complex. This dissertation further focused on transition metal-mediated carbene transfer to olefins is a common synthetic route towards cyclopropanation. The synthesis and reactivity of a remote carbene at mononuclear Fe(OR)2 centers was investigated. This study was inspired by a previous study of our group, which demonstrated that the reaction between a Co(II) bis(alkoxide) precursor and diazoalkanes led to a formally Co(IV) carbene complex. This complex exhibited carbene transfer to isocyanides to form ketenimines. However, no cyclopropanation reactivity was observed. In contrast, the reaction of an Fe(II) bis(alkoxide) complex with diazoalkanes and diazoesters resulted in the reductive coupling of the diazo functionality through the terminal nitrogens; no carbene formation was observed. As an alternative approach towards reactive carbene functionality: replacement of the diazo carbene precursors with hypervalent iodine carbene precursors was attempted. The addition of PhIC(CO2Me)2 to a solution of Fe(OR)2(THF)2 and styrene led to formation of the corresponding cyclopropane in good yield. The optimum reactivity was observed for the stoichiometric ratio of 2:1 between PhIC(CO2Me)2 and styrene. A series of different olefin precursors including styrenes with various electronic properties were investigated. For most of the para-substituted styrenes, moderate to excellent yields are observed; good to excellent yields are also observed for the α-methylstyrene. For some styrenes (4-methoxo, 4-trifluoromethyl), all three iron(II) bis(alkoxide) catalysts generally exhibit similar reactivity. In contrast, some variability is observed for other styrenes (unsubstituted or 4-cyano). There appears to be higher reactivity for the electron-rich (4-tert-butyl, 4-methoxy) vs. electron-poor (4-trifluoromethyl, 4-cyano) substrates. No cyclopropanation was observed for β-methylstyrene, 1-decene, or methyl acrylate. Based on computational studies, the formation of a remote carbene radical, Fe(OR)2(κ2- (O=C(OMe))2C) was hypothesized based on the ability of [Fe(OR)2] to coordinate an iodonium ylide precursor in κ2-O,O-coordination mode, and the tendency of [Fe(OR)2] to undergo oxidation to Fe(III). The attempts to isolate the reactive iron-carbene intermediate invariably resulted in the formation of (MeO2C)2C=C(CO2Me)2 and PhI; however, the spectroscopical analysis of the reactions, including reactions with H atom donor reagents, also strongly suggested that a novel remote carbene radical intermediate mediates the reaction. Following the observation of efficient group transfer reactivity and facile ring opening polymerization reactivity of achiral transition metal bis(alkoxide) catalysts in previous studies, the development of a new chiral bis(alkoxide) ligand investigation of its coordination chemistry with 3d and main-group metals was inspired. Initially, the synthesis of H2[OO]Ph,Me was attempted which was unsuccessful due to the acidity of methyl hydrogens in phenyl methyl ketone leading to the ketone deprotonation forming a singly substituted product. As an alternative, a comparable substrate lacking α-protons, phenyl trifluoromethyl ketone was utilized. Herein, a new chelating bis(alkoxide) ligand featuring two stereocenters, H2[OO]Ph,CF3. The ligand was obtained as a mixture of homochiral (RR/SS) and heterochiral (RS) diastereomers, which were subsequently separated by column chromatography. Both separated products were characterized by NMR spectroscopy (1H, 13C, 19F), strongly suggesting the formation of the diastereomers. X-ray crystal structures of both isomers which were aollected in anti-form, confirmed the stereochemistry of the diastereomers; homochiral (RR/SS) nature of the rac-isomer and the heterochiral (RS) nature of the meso-isomer.

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