A trans-palladium dichloride complex with a bulky organosulfur ligand: syntheses, structure, and applications in catalytic alkylation of acetophenone and secondary alcohols using alcohols

Abstract

In this report, we have presented the synthesis of a bulky organosulfur ligand (L1) with two naphthalene molecules in it. The trans-palladium dichloride complex (C1) of L1 was synthesized from a reaction with the PdCl₂(CH₃CN)₂ precursor. The newly synthesized molecules (L1 and C1) were characterized using standard spectroscopic and analytical techniques. The single crystal X-ray analysis of C1 revealed a square planar geometry with an inversion center in the molecule. The ligands showed trans orientation with respect to the palladium center with four bulky naphthalene units in it. The complex possesses intramolecular SCH⋯Cl interactions of 2.582 Å between the bulky organosulfur ligand and palladium dichloride. C1 is designed in such a way that four bulky naphthalene units surround the catalytically active palladium center and using C1 as a catalyst will offer unique selectivity features during catalysis. Taking cognizance of this, C1 was used as a catalyst for α-alkylation of acetophenone and β-alkylation of secondary alcohols. A broad substrate scope can be activated for achieving yields up to 89%, using 0.5 mol% C1 under mild reaction conditions. Intriguingly, the developed synthetic methodology was extended for direct one-pot syntheses of quinoline derivatives. A plausible reaction mechanism was proposed based on the control experiments and earlier reports. The poisoning experiments suggested a homogeneous nature of the catalysis reaction. Since the only by-product of the reaction is H₂O, the developed catalysis protocol is a greener and sustainable alternative for the production of such ketone derivatives.