Phosphine CN-palladacycles catalyzed regioselective alkoxycarbonylation of styrenes

Title : Phosphine CN-palladacycles catalyzed regioselective alkoxycarbonylation of styrenes

Abstract:

Carbonylation reactions represent an important strategy for the synthesis of carbonyl-containing compounds. Palladium-catalyzed carbonylation has emerged as a versatile methodology due to its ability to transform a broad range of substrates while providing high catalytic activity and excellent regioselectivity. In particular, palladacycles are attractive catalytic precursors because these organometallic compounds are air- and moisture-stable, allowing for easy handling and storage without requiring strict conditions, and have proven effective in numerous palladium-catalyzed transformations. However, in carbonylation processes, palladacycle-based catalysts have been used solely for the alkoxycarbonylation of aryl halides. Following our interest in Pd-catalyzed carbonylation reactions, we applied CN-palladacycles in the alkoxycarbonylation of olefins because these complexes contain Pd (II) centers, and Pd (II) species are usually involved in palladium-mediated alkoxycarbonylation of unsaturated compounds. Additionally, phosphine ligands can modulate the linear (L) or branched (B) regioselectivity in the carbonylation reactions (Scheme 1, A).
In this work, we synthesized a series of CN-palladacycles (4a-e) stabilized by monodentate phosphines. These palladacycles demonstrated high stability to moisture and were successfully characterized by spectroscopic techniques such as ¹H NMR, ¹³C{¹H} NMR, ³¹P{¹H} NMR, MS, and elemental analysis. Palladacycles 4a-e were successfully applied in the alkoxycarbonylation of styrene. The results demonstrated that the phosphine ligand and substituents on the imine influence catalytic activity (Scheme 1, A). Using the most active phosphine CN-palladacycle precatalyst (4c), the substrate scope was evaluated with various styrene derivatives and primary, secondary, and tertiary alcohols (Scheme 1, B), resulting in esters (3a-w) with yields ranging from moderate to excellent (20-99%). This catalytic system exhibited remarkable regioselectivity, favoring branched esters (5:95-1:99 L:B).

Biography:

Ph.D. student in Chemistry at National Autonomous University of Mexico, specializing in catalysis and carbonylation. Research interests include catalyst development, reaction mechanisms, and sustainable synthetic methodologies.Ph.D. student in Chemistry at National Autonomous University of Mexico, specializing in catalysis and carbonylation. Research interests include catalyst development, reaction mechanisms, and sustainable synthetic methodologies.