The Effects of Ancillary Ligands on Metal–Carbon Bond Strengths as Determined by C–H Activation

Ruthenium-Catalyzed Site-Selective Intramolecular Silylation of Primary C-H Bonds for Synthesis of Sila-Heterocycles

Incorporating the silicon element into bioactive organic molecules has received increasing attention in medicinal chemistry. Moreover, organosilanes are valuable synthetic intermediates for fine chemicals and materials. Transition metal-catalyzed C-H silylation has become an important strategy for C-Si bond formations. However, despite the great advances in aromatic C(sp²)-H bond silylations, catalytic methods for aliphatic C(sp³)-H bond silylations are relatively rare. Here we report a pincer ruthenium catalyst for intramolecular silylations of various primary C(sp³)-H bonds adjacent to heteroatoms (O, N, Si, Ge), including the first intramolecular silylations of C-H bonds α to O, N, and Ge. This method provides a general, synthetically efficient approach to novel classes of Si-containing five-membered [1,3]-sila-heterocycles, including oxasilolanes, azasilolanes, disila-heterocycles, and germasilolane. The trend in the reactivity of five classes of C(sp³)-H bonds toward the Ru-catalyzed silylation is elucidated. Mechanistic studies indicate that the rate-determining step is the C-H bond cleavage involving a ruthenium silyl complex as the key intermediate, while a η²-silene ruthenium hydride species is determined to be an off-cycle intermediate.

Mild metal-catalyzed C–H activation: examples and concepts

C–H Activation reactions that proceed under mild conditions are more attractive for applications in complex molecule synthesis. Mild C–H transformations reported since 2011 are reviewed and the different concepts and strategies that have enabled their mildness are discussed.