Abstract:
Aluminum is one of earth’s most abundant and cheapest metals, and it is also nontoxic
and environmentally friendly. This makes it an ideal candidate to be implemented in
organometallic chemistry as a greener alternative to metal-based systems based on heavy
and/or precious metals. One of the realms in which aluminum and other group 13
elements show promise is metal-ligand cooperative chemistry, which can afford
transition metal-reminiscent small molecule activation chemistry. Our studies of organic
ligands with nitroxide-functionalities within Al and Ga coordinative systems has led us to
the discovery of tripodal tris(nitroxide) Al and Ga complexes with abilities to engage in
metal-ligand cooperativity, including in their reaction with small molecule alcohol
substrates. In an effort to better understand the mechanism of the O-H bond activation
mechanism exhibited by these complexes, we report the results of various kinetics
experiments that explore how alcohol O-H acidity (pKa) and metal center (Al, Ga) affect
reaction rate, as well as an observable kinetic isotope effect. We also report the results of
the screening of various alcohol substrates with these complexes, and find a strong
correlation between general reactivity and alcohol acidity.
