Synthesis, Isolation and Structural Elucidation of Cage-Shaped Aluminum and Gallium Phosphorous Aryloxide Complexes as Highly Reactive Lewis Acids and Carboxyboranes as Carbon Monoxide Releasing Molecules (CORMs)

Abstract

Group 13 Lewis acids have gained a lot of interest in over the years due to their reactivity, potency, and applications in the field of catalysis. Generally, there is a direct relationship between the catalytic activity of the organometallic Lewis acid and its acidity. However, this gives rise to a bigger challenge which is related to the stability of the catalyst. Our preliminary results from working on the catalytic reduction of CO2 have shown catalytic deactivation after one or two cycles. Utilizing bulkier substituents such as monodentate phenolates have shown promising increased stability and reactivity. The structural optimization (i.e., open-shape and cage-shape complexes) of the cationic species along with the use of suitable counterions such as weakly coordinating anions (WCAs), can be used to fine tune stability and reactivity to the desired outcome. This work describes the synthesis and spectroscopic characterization of a series of cage-shaped phosphorous aluminum and gallium complexes MX[O3PY] (M= Al, Ga, X= Cl, Et), (Y= H, O) as potential highly reactive aluminum and gallium Lewis acids. Additionally, various attempts to activate the Lewis acid center are discussed. Furthermore, the role of carbon monoxide (CO) is found to be neuroprotective and neurotherapeutic in many studies as it can protect cells against (Aβ1-42) toxicity which are the main characteristic for the diagnosis of Alzheimer’s disease (AD) and other neurodegenerative diseases. This works highlights a class of the bioactive boron analogs known as carboxyboranes (A-BH2COOH, A= Amine), their synthesis, and derivatization as potential nonmetallic carbon monoxide releasing compounds via hydrolysis under physiological pH and temperature. Different approaches towards the synthesis and derivatization of such bioactive compounds will be illustrated.