Magnesium-Mediated Cyanosilylation and Hydroboration of Arene and N-Heteroarene Aldehydes: An Experimental and Theoretical Study.

Abstract

In recent years, there has been a noteworthy expansion in the field of main-group compounds, attributed to their intrinsic capacity for the activation of small molecules. In this regard, the alkaline earth metal complexes have garnered important attention. Herein, we showed the utilization of a Mg complex Mg-1 as a catalyst in cyanosilylation reactions involving several aromatic and aliphatic aldehydes, conducted under mild reaction conditions. Although complex Mg-1 demonstrated its effectiveness in this transformation, complexes Mg-2 and Mg-3 yielded lower amounts of cyanosilylated products, highlighting the influence of the ligand spacer in catalytic activity. To further assess this effect, a mononuclear magnesium complex, Mg-4, was synthesized and the catalytic performance of Mg-4 in the cyanosilylation of aldehydes was found to be lower than that of Mg-1. This study establishes that magnesium complexes can independently catalyze the cyanosilylation of aldehydes, with those featuring an oxygen-bridged spacer exhibiting enhanced catalytic efficiency. Furthermore, employing complex Mg-1, we explored the cyanosilylation and hydroboration reactions involving N-heteroarene carboxaldehyde, an area with limited substrate scopes. Experimental and theoretical studies were performed to establish the mechanism which shows that the cyanosilylation reaction initiates with the initial coordination of trimethylsilyl cyanide (TMSCN) with the catalyst, followed by the subsequent attack of aldehydes. Whereas, in the hydroboration reaction, HBpin first reacts with the Mg complex Mg-1 to form Mg-H, which subsequently reacts with the aldehyde to form a hydroborylated product via a four-membered transition state.