Divergent catalysis: elucidation of ligand-controlled chemo-divergent Pd-catalyzed intramolecular allene-silacyclobutane reactions

In this work, building upon our previous discovery that structurally distinct phosphine ligands can effectively modulate palladium-catalyzed intramolecular allene-silacyclobutane reactions to afford two different seven-membered silacyclic products, herein we further demonstrated that using DPPF as ligand leads to the formation of a novel polysubstituted silane compounds containing three distinct types of alkenyl groups. This finding significantly expands the scope of divergent catalysis using identical metal catalyst and substrate. Through combined experimental and computational studies, we have comprehensively elucidated the reaction mechanism, in which the reaction is initiated by silicon-carbon bond activation of the silacyclobutane moiety, followed by allene insertion to form a seven-membered palladacycle as the key intermediate. The subsequent reaction pathways diverge due to the ligand-dependent modulation of reductive elimination versus β-H elimination processes. Furthermore, the ring-open intermediates of silacyclobutane moiety can undergo additional divergent pathways through either reductive elimination or 1,3-migration shift of the palladium intermediate, resulting in three distinct types of products for this divergent catalysis-based transformation.