Toward Sustainable Metal-Free Catalysis: Synthesis and Reactivity of Oxygen-Substituted Silicon Complexes in a Xanthene-Based Pincer Framework

Abstract

Industrial catalysis is reliant on transition metal catalysts, which are often scarce, expensive, environmentally detrimental, and toxic. Though traditionally viewed as not well-suited for catalysis, research in the past several decades has illuminated the potential for main group elements to facilitate catalytic transformations. Silicon, the second most abundant element in the Earth’s crust, would represent a sustainable, cheap, and nontoxic replacement for transition metals. In particular, silylenes are of interest due to their amphoteric site which resembles the partially filled d-orbitals of transition metals, however, the body of work on isolable silylenes is small. This work targeted the synthesis of a novel silylene supported by an LX2 (O,O,O) xanthene-based pincer ligand, which would represent the first oxygen-substituted monosilylene and the first neutral silylene within a pincer ligand framework. Dichlorosilane and hydridochlorosilane complexes within the novel ligand scaffold were synthesized. Attempts to access the corresponding silylene revealed that these silanes are highly robust, and are exceptionally privileged for substitution reactivity due to steric accessibility and electronic deficiency at the silicon center.