Assessing the environmental benefit of palladium-based single-atom heterogeneous catalysts for Sonogashira coupling. Issue 18 (12th July 2022)

• Record Type: Journal Article
• Authors: Faust Akl, D.; Poier, D.; D'Angelo, S. C.; Araújo, T. P.; Tulus, V.; Safonova, O. V.; Mitchell, S.; Marti, R.; Guillén-Gosálbez, G.; Pérez-Ramírez, J.
• Is Part Of: Green chemistry. Volume 24:Issue 18(2022)
• Page Start: 6879
• Page End: 6888
• Publication Date: 2022-07-12
• Subjects: Environmental chemistry -- Industrial applications -- Periodicals; Environmental management -- Periodicals; 660
• DOI: 10.1039/d2gc01853e
• Languages: English
• ISSNs: 1463-9262

Abstract

Abstract : We quantify through life cycle analysis the environmental benefits of replacing homogeneous with heterogeneous palladium catalysts in Sonogashira coupling and demonstrate the potential of single-atom catalysts (SAC) to lower the footprint. Abstract : The Pd–Cu catalysed Sonogashira coupling of terminal alkynes and aryl halides is a cornerstone synthetic strategy for C–C bond formation. Homogeneous organometallic systems conventionally applied are typically not reusable and require efficient downstream Pd removal steps for product purification, making it challenging to fully recover the precious metal. A holistic cradle-to-gate life cycle assessment (LCA) unveils that process footprint can be improved up to two orders of magnitude from repeated catalyst reuse. New classes of heterogeneous catalysts based on isolated metal atoms (single-atom catalysts, SACs) demonstrate promising potential to synergise the benefits of solid and molecular catalysts for efficient Pd utilisation. Here we show that using Pd atoms anchored on nitrogen-doped carbon permits full recovery of the metal and reuse of the catalyst over multiple cycles. A hybrid process using the Pd-SAC with a homogeneous CuI cocatalyst is more effective than a fully heterogeneous analogue based on a bimetallic Pd–Cu SAC, which deactivates severely due to copper leaching. In some scenarios, the LCA-based metrics demonstrate the footprint of the hybrid homogeneous–heterogeneous catalytic process is leaner than the purely homogeneous counterpart already upon single reuse. Combining LCA with experimental evaluation will be a useful guide to the implementation of solid, reusable catalysts for sustainable organic transformations.