Linkage Isomers of Triangular Pd Metallacycles and Catalysis in Aqueous Suzuki Coupling Reaction

• Published in: Inorganic chemistry 2024-01, Vol.63 (2), p.1427-1438
• Main Authors: Chaudhari, Kamal R., Wadawale, Amey P., Pathak, Arup Kumar, Dey, Sandip
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.3c03963

The water-soluble trinuclear Pd metallacycles [Pd­(tmeda)­(4-Spy)]3(X)3 (tmeda = tetramethylethylenediamine, X = OTf, 2; NO3, 3) were synthesized from the ambidentate ligand 4-pyridylthiolate (Spy–) and [Pd­(tmeda)­X2] in 80 and 70% yield, respectively. Two possible linkage isomers are found in solution (slow interconversion found in the NMR) and in the solid state. Density functional calculations showed that the energy of the isomer with a D3-symmetric arrangement of the SPy ligand and all Pd atoms having N∧NPdSN coordination is only 7 kcal/mol lower. When reacting [Pd­(tmeda)­(NO3)2] with 4,4′-biphenyldithiolate (S2bph2–), the tetranuclear [{Pd­(tmeda)}4(μ-S2bph)2]­(NO3)4 (1) was formed. A new type of undecanuclear Pd cluster was separated as a minor product from an acetone solution of 2 in air. The new complexes represent the first examples of water-soluble Pd metallacycles constructed from a pyridine-thiolate ligand. They show catalytic activity with turnover numbers ranging from 9 to 420 in aqueous Suzuki cross-coupling reactions using phenyl boronic acid and a number of aryl halides. An optimized system gave a TON of 6,900,000 and a TOF of 492,857 h–1. The catalyst could be reused eight times, and the activity has been attributed to the formation of PdNPs.