From recovered metal waste to a promising catalyst for C-H functionalisation and C-N amination Khairil Jantan 1,2 , Gregor Ekart 1 Angela Serpe 3 , James D. E. T. Wilton-Ely 1 1 Imperial College London, UK, 2 Universiti Teknologi MARA (UiTM), Malaysia, 3 University of Cagliari, Italy Palladium-mediated reactions are among the most frequently used transformations in organic chemistry, although palladium (Pd) is only present in low abundance in a few places on earth. Palladium mining using conventional methods is extremely harmful to the environment and is unsustainable due to the lack of natural reserves. An accumulation of large palladium-containing waste can be a sustainable source of palladium in the future (urban mining) but this requires less energy-intensive recovery processes to be implemented. Serpe and colleagues 1 reported the first selective and non-acidic dissolution of palladium from a model spent catalytic converter using the dithioxamide lixiviant Me 2 dazdt×2I 2 in an organic solvent under mild conditions to form [Pd(Me 2 dazdt) 2 ] 2+ as the recovery product. This palladium complex was found to be highly active towards the C-H bond functionalisation of benzo[ h ]quinoline and 8-methylquinoline, 2 competing favourably with leading systems reported in the literature using Pd(OAc) 2 , sourced from conventional mining. 3 However, the use of expensive starting materials and Lawesson’s reagent to form the dithioxamide Me 2 dazdt reduces the economic and environmental benefits of this ligand. 4 A new, low-energy route to selectively extract palladium from metal waste has now been developed, 5 which generates the dimer ( n NBu 4 ) 2 [Pd 2 I 6 ] as the palladium recovery product. This contribution describes an effective way of valorising this complex for direct use as a homogeneous catalyst in C-H functionalisation and C-N bond amination. Using simple ligand exchange reactions, an analogue of a well-known catalyst, PdI 2 (dppf), was synthesised from the recovery product to provide a phosphine-supported derivative. Preliminary results indicate encouraging catalyst reactivity in oxidative C-H functionalisation and C-N amination reaction of a range of different substrates with relevance to pharmaceutical chemistry and the production of fine chemicals. This approach aims to provide potential solutions to the major issue of sustainability in palladium-mediated catalysis. 6 References 1. A. Serpe, F. Bigoli, M. C. Cabras, P. Fornasiero, M. Graziani, M. L. Mercuri, T. Montini, L. Pilia, E. F. Trogu and P. Deplano, Chem. Commun. , 2005, 8 , 1040–1042. 2. K. A. Jantan, C. Y. Kwok, K. W. Chan, L. Marchio, A. J. P. White, P. Deplano, A. Serpe and J. D. E. T. Wilton-Ely, Green Chem. , 2017, 19 , 5846–5853. 3. A. R. Dick, K. L. Hull and M. S. Sanford, J. Am. Chem. Soc. , 2004, 126 , 2300–2301. 4. K. A. Jantan, K. W. Chan, L. Melis, A. J. P. White, L. Marchiò, P. Deplano, A. Serpe and J. D. E. T. Wilton-Ely, ACS Sustain. Chem. Eng. , 2019, 7 , 12389 -12398. 5. M. Cuscusa, A. Rigoldi, F. Artizzu, R. Cammi, P. Fornasiero, P. Deplano, L. Marchiò and A. Serpe, ACS Sustain. Chem. Eng. , 2017, 5 , 4359–4370. 6. S. McCarthy, D. C. Braddock and J. D. E. T. Wilton-Ely, Coord. Chem. Rev. , 2021, 442 , 213925.
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