- Bulky Selenium Ligand Stabilized Trans-Palladium Dichloride Complexes as Catalyst for Silver-Free Decarboxylative Coupling of Coumarin-3-Carboxylic Acids
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This report describes the syntheses of three new trans-palladium dichloride complexes of bulky selenium ligands. These complexes possess a Cl?Pd?Cl rotor spoke attached to a Se?Pd?Se axle. The new ligands and palladium complexes (C1?C3) were characterized with the help of NMR, HRMS, UV-Vis., IR, and elemental analysis. The single-crystal structure of metal complex C2 confirmed a square planar geometry of complex with trans-orientation. The X-ray structure revealed intramolecular secondary interactions (SeCH—Cl) between chlorine of PdCl2 and CH2 proton of selenium ligand. Variable-temperature NMR data shows coalescence of diastereotopic protons, which indicates pyramidal inversion of selenium atom at elevated temperature. The relaxed potential energy scan of C2 suggests a rotational barrier of ~12.5 kcal/mol for rotation of chlorine atom through Cl?Pd?Cl rotor. The complex C3 possesses dual intramolecular secondary interactions (OCH2—Cl and SeCH2—Cl) with stator ligand. Molecular rotor C2 was found to be a most efficient catalyst for the decarboxylative Heck-coupling under mild reaction conditions. The protocol is applicable to a broad range of substrates with large functional group tolerance and low catalyst loading (2.5 mol %). The mechanism of decarboxylative Heck-coupling reaction was investigated through experimental and computational studies. Importantly the reaction works under silver-free conditions which reduces the cost of overall protocol. Further, the catalyst also worked for decarboxylative arylation and decarboxylative Suzuki-Miyaura coupling reactions with good yields of the coupled products.
- Meena, Neha,Kumar, Sunil,Shinde, Vikki N.,Reddy, S. Rajagopala,Himanshi,Bhuvanesh, Nattamai,Kumar, Anil,Joshi, Hemant
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supporting information
(2022/01/11)
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