Iron electronic delocalization enables catalytic selective trisilyla-tion: beyond steric hindrance

The efficient synthesis of sterically congested tetrasubstituted alkenes, particularly the synthetically valuable 1,1,2-trisilylalkenes, remains a longstanding challenge due to significant steric hindrance encountered during the bond formation. Here, we report an iron-catalyzed trisilylation of ynamides that leverages iron electronic delocalization to modulate the character of double bonds toward that of single bonds, effectively mitigating steric constraints during the reaction. This strategy enables a regioselective and controllable synthesis of 1,1,2-trisilylated alkenes, trans-1,2-disilylated alkenes, and monosilylated alkynes under mild conditions with high efficiency. Notably, the method allows for late-stage functionalization of biologically relevant molecules, offering a valuable platform for the structural diversification of alkynes. In addition, the resulting multisilylated intermediates undergo diverse downstream transformations, granting access to a broad array of otherwise elusive tetrasubstituted silylalkenes. Experimental and computational studies reveal that monosilylalkynes serve as key intermediates, with β-N elimination, double migratory insertion, and reductive elimination steps likely involved in the catalytic cycle. This work provides fundamental insights into the construction of sterically hindered chemical bonds via base metal catalysis and underscores the potential of iron to unlock unconventional reactivity through electronic delocalization effects.