Mechanistic Studies of Oxygen Activation and Atom Transfer Reactions with Mononuclear Vanadium(III), Iron(II), and Palladium(0) Complexes.
Abstract: This thesis comprises the area of oxygen binding, activation, and
related oxygen atom transfer processes promoted by mononuclear transition metal complexes
of vanadium(III), iron(II), and palladium(0). The first part of this thesis details the
mechanistic studies of ligand binding and oxygen atom transfer (OAT) reactions to the
three-coordinate complex VIII(N[tBu]Ar)3 (Ar = 3,5-Me2C6H3). ... read moreThe kinetics of OAT to
V(N[tBu]Ar)3 from N2O and other N-oxides is presented in Chapter 1, which revealed a wide
range of kinetic behavior influenced by the mode and strength of coordination of the
N-oxide and its ease of atom transfer. The importance of ligand binding, the initial step
in the OAT reaction, is highlighted. Chapter 2 presents the kinetics of nitrile (RCN)
binding to V(N[tBu]Ar)3, which serves as a comparative study with Mo(N[tBu]Ar)3. Studies
revealed much faster binding of nitriles to V(N[tBu]Ar)3, which coordinate exclusively in
an η1-fashion. The differences in binding rates and affinities due to metal
substitution are emphasized. The kinetic study of dioxygen binding to V(N[tBu]Ar)3 is
presented in Chapter 3. Formation of the novel (η2-O2)V(N[tBu]Ar)3 adduct proceeds
through a biphasic process involving rapid formation of (η1-O2)V(N[tBu]Ar)3 which
subsequently isomerizes to the η2-O2 product. The rates of formation and
interconversion of (η1-O2)V(N[tBu]Ar)3 and (η2-O2)V(N[tBu]Ar)3 were
quantified. Chapter 4 details the mechanistic study of dioxygen binding to Pd0(IPr)2 (IPr =
1,3-bis(2,6-diisopropyl)phenylimidazol-2-ylidene), which forms an unprecedented
trans-(η1-O2)2Pd(IPr)2 adduct. The unstable (η2-O2)Pd(IPr)2 intermediate
forms at low temperatures and reacts further with O2 at higher temperatures to produce
trans-(η1-O2)2Pd(IPr)2. The reaction is proposed to proceed through a steady state
(η1-O2)Pd(IPr)2 intermediate that can trap a second molecule of O2 to form the
unique final product. This work highlights how subtle changes in ligand sterics
dramatically affect the relative stabilities of (η2-O2)Pd(NHC)2 (NHC =
N-heterocyclic carbene) adducts. The comparative study of biomimetic non-heme iron
complexes supported by aminopyridine macrocyclic ligands (PyMACs) is presented in Chapter
5, including the preparation of two novel complexes that are potent oxygenation catalysts.
This work highlights the effect of the axial donor on the structure and reactivity towards
olefin epoxidation and provides preliminary insight into the nature of reactive
Thesis (Ph.D.)--Tufts University, 2015.
Submitted to the Dept. of Chemistry.
Advisor: Elena Rybak-Akimova.
Committee: Robert Stolow, Terry Haas, and Peter Mueller.
Keywords: Chemistry, and Inorganic chemistry.read less