Multi-Dentate Phosphine Ligand Derived from Cyclotetrasiloxane and Its Application in Palladium-Catalyzed Alkoxycarbonylation of Alkenes

The development of phosphine ligands continues to be essential for palladium-catalyzed homogeneous carbonylation reactions, particularly in achieving high regioselectivity. In this study, a cyclosiloxane-based multi-dentate phosphine ligand, L1 (V4-4Ph₂P), characterized by its high thermal stability and oxidation resistance, was synthesized through the radical addition of secondary phosphines to the double bonds of tetravinyltetramethylcyclotetrasiloxane. L1 was then used in the Pd-catalyzed alkoxycarbonylation of a variety of olefins, including terminal and internal alkenes, cyclic alkenes, aromatic terminal alkenes as well as tetra-, tri- and 1,1-disubstituted alkenes to afford the desired esters with moderate to good yields. As elucidated via DFT calculations and in situ IR spectroscopy, the optimum spatial chelation modes and high stability of Pd−H active species were responsible for the enhancement of catalytic efficiency.