Palladium(0) Catalyzed Synthesis of (E)-4-Bromo-N-((3-bromothiophen-2-yl)methylene)-2-methylaniline Derivatives via Suzuki Cross-Coupling Reaction: An Exploration of Their Non-Linear Optical Properties, Reactivity and Structural Features

Abstract

A series of (E)-4-bromo-N-((3-bromothiophen-2-yl)methylene)-2-methylaniline analogs synthesized in considerable yields through Suzuki cross-coupling reactions. Various electron donating and withdrawing functional moieties were successfully incorporated under the employed reaction conditions. Reaction of 4-bromo-2-methylaniline (1) with 3-bromothiophene-2-carbaldehyde (2b) in the existence of glacial acetic acid, provided (E)-4-bromo-N-((3-bromothiophen-2-yl)methylene)-2-methylaniline (3b) in excellent yield (94%). Suzuki coupling of 3b with different boronic acids in the presence of Pd(PPh3)4/K3PO4 at 90 °C led to the synthesis of the monosubstituted and bisubstituted products 5a–5d and 6a–6d in moderate yields (33–40% and 31–46%, respectively). Density functional theory (DFT) investigations were performed on different synthesized analogues 5a–5d, 6a–6d to determine their structural characteristics. The calculations provide insight into the frontier molecular orbitals (FMOs) of the imine-based analogues and their molecular electrostatic potential (MESP). Reactivity descriptors like ionization energy (I), electron affinity (A), chemical hardness (ƞ) and index of nucleophilicity have been calculated for the first time for the synthesized molecules.