Thesis (Ph. D.)--University of Rochester. Department of Chemistry, 2020.
Reducible metal oxides (RMOs) are widely used materials in heterogeneous
catalysis due to their ability to facilitate the conversion of energy-poor substrates to energyrich
chemical fuels and feedstocks. Theoretical investigations have modeled the role of
RMOs in catalysis and found they traditionally follow a mechanism in which the generation
of oxygen-atom vacancies is crucial for the high activity of these solid supports. However,
limited spectroscopic techniques for in situ analysis renders the identification of the
reactivity of individual oxygen-atom vacancies on RMOs challenging. These obstacles can
be circumvented through the use of homogenous complexes as molecular models for metal
oxides. Polyoxometalates, in particular, have emerged as promising materials toward
modelling heterogenous systems due to their comparable metal-oxide surface structure and
electronic properties. Summarized herein, a sub-class of polyoxometalates,
polyoxovanadate-alkoxide (POV-alkoxide; [V6O7(OR)12]n; R=CH3, C2H5) clusters, are
explored as atomically-precise molecular models for bulk vanadium oxide. Chapter 2
describes initial investigations into the post synthetic modification of these polynuclear
assemblies, demonstrating the ability to generate one or two oxygen-deficient sites on
[V6O7(OR)12]n (n = 1-, 0, 1+) via V=O bond cleavage. This resulted in the unprecedented
formation of oxygen-deficient clusters that feature coordinatively unsaturated VIII ions (e.g.
[V6O6(OCH3)12]n, [V6O5(OCH3)12]0; n = 1-, 0). Chapter 3 expands on this work,
demonstrating that a series of tertiary phosphines with varying nucleophilicities can also
mediate V=O bond cleavage. Analysis of the steric influence of the bridging alkoxides
surrounding the vanadyl moieties on oxygen atom transfer (OAT) revealed that the alkoxide chain length significantly influences the rate of O-atom abstraction. Initial
investigations into the deoxygenation of an organic substrate, styrene oxide, was also
presented. Chapter 4 focuses on using these oxygen-vacant POV-alkoxides as functional
models for metal oxides through investigating reductive transformations such as O2 and
NOx1- (x = 2, 3) reduction. These results suggest that the oxygen-deficient cluster follows
a similar mechanism to that of RMOs including substrate coordination to the oxygenvacant
site, reduction, E-O bond cleavage, and ultimately, OAT. Furthermore, analysis of
the influence of surface ligands, oxidation state distribution of remote vanadyl ions, and
ion-pairing interactions revealed that these physiochemical properties significantly
influence the rate of substrate reduction. Overall, the post-synthetic modification of POValkoxide
clusters has presented an opportunity to analyze the structural and electronic
consequences of oxygen-atom abstraction as well as probe new reactivity with epoxides,
nitrogen-containing oxyanions, and small gaseous molecules.
Finally, Chapter 5 presents the expansion of manganese (II) chloride for the
catalytic generation of C(sp2)-C(sp3) bonds via Kumada cross-coupling. Selective
formation of 2-alkylated N-heterocyclic complexes were observed in high yields with use
of 3 mol% MnCl2THF1.6 and under ambient reaction conditions (21 oC, 15 min-20 hr).
Preliminary investigations into the use of 2-thioether coupling partners were explored,
showing up to 57% cross-product with n-butylmagnesium chlorine. In addition, the
synthesis of potential catalytically active species are presented, revealing synthetic routes
to accessing manganese-alkyl and manganese-halide dimers.
