Detailed mechanistic investigation of iron-catalysed Sonogashira coupling: A DFT study

The Sonogashira coupling reaction has emerged as a pivotal transformation in organic synthesis, facilitating the construction of carbon-carbon bonds between aryl or vinyl halides and terminal alkynes. Conventionally, palladium catalysts have dominated this field; however, the increasing demand for sustainable and cost-effective catalytic systems has prompted a re-evaluation of alternative transition metals. Iron, with its abundant and environment-friendly nature, has recently gained prominence as a potential catalyst for Sonogashira coupling. This work delves into the catalytic capabilities of iron in Sonogashira coupling reactions, aiming to provide a comprehensive understanding of its mechanistic intricacies. Through a systematic investigation, we intend to shed light on the role of iron in the cross-coupling of para- iodoacetophenone and phenyl acetylene in aqueous medium, addressing challenges related to devising of the active catalyst, intermediates and transition states involved in the pathway. A model system of iodobenzene and phenyl acetylene were chosen for the study for which a concerted mechanism was found to be favourable. The activation barrier which showed up 31.15 kcal/mol concorded well with the expeeimental values. The mechanistic insights gained through the study will aid in the design and development of novel iron catalysts.