Bulky Selenium Ligand Stabilized Trans‐Palladium Dichloride Complexes as Catalyst for Silver‐Free Decarboxylative Coupling of Coumarin‐3‐Carboxylic Acids

Abstract

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.

Titania Nanorod-Supported Mercaptoundecanoic Acid-Grafted Palladium Nanoparticles as a Highly Reusable Heterogeneous Catalyst for Substrate-Dependent Ullmann Coupling and Debromination of Aryl Bromides

“…The deactivated derivative, bromobenzene, resulted in a 73% yield of coupled product 2d . The acid group which is prone to a decarboxylative coupling reaction with a Pd catalyst showed excellent tolerance toward the protocol and resulted in a 66% yield of coupled product 2e . Other functional groups, like −NO 2 and −CN, which are sensitive toward Pd-catalyzed reduction reactions, also showed good tolerance toward the protocol and resulted in good yields (54–57%) of coupled products 2f and 2g .…”

Recent Advances in the Decarboxylative Strategy of Coumarin‐3‐carboxylic Acid

“…In 2021, Meena and co‐workers developed a palladium complex which was capable of performing a silver‐free decarboxylative coupling reaction of coumarin‐3‐carboxylic acid 1 (Scheme 12). [31] The reactions under consideration were Heck and Suzuki type of decarboxylative coupling reaction. For the enhancement of the reaction condition used by trivial methods, they developed bulky selenium ligand stabilized trans‐palladium dichloride complex, which functions as a suitable catalyst.…”

A palladium complex of a macrocyclic selenium ligand: catalyst for the dehydroxymethylation of dihydroxy compounds

“…Tuning ligand design for achieving selectivity during catalysis is a viable solution for addressing such issues. 2 Metal complexes where the central metal is present in sterically confined spheres showed excellent potential for catalysis, leading to better activities and selectivities. 3 The steric bulk of the ligand forces the incoming reagents to approach the metal through specific orientations which leads to the regioselectivity in products during catalysis.…”