Solvent-free cyanosilylation of aromatic and heteroaryl aldehydes catalyzed by a cationic iron N-heterocyclic carbene complex at ambient temperature under UV irradiation

Abstract

The cyanosilylation of aromatic aldehydes and heteroaryl aldehydes with trimethylsilyl cyanide (TMSCN) is efficiently catalyzed by an iron complex of the type {[3-isopropyl-1-(1R-phenylethyl)imidazol-2-ylidene]Fe(CO)2}I (3) in presence of UV light (λ = 294 nm) in moderate to excellent yields under ambient temperature. The heteroaryl aldehydes exhibited higher yields than the aromatic ones, and the aromatic aldehydes, bearing electron donating groups (EDG), exhibited higher yields over the ones with the electron withdrawing groups (EWG). A proposed catalytic cycle initiates with an active species (A), formed by the dissociation from the iron complex (3), and proceeds via an aldehyde activated species (B), and that upon reaction with TMSCN gives the desired cyanosilylated product. Quite significantly, the initial active iron species (A) and the iron-bound α-cyanobenzyloxy species (C) have been detected by mass spectrometry. Additionally, the formation of species (C) was further corroborated by the observation of the formation of TMSI in 29Si NMR experiment.