E–H (E = B, Si, C) Bond Activation by Tuning Structural and Electronic Properties of Phosphenium Cations

In this work, strategic enhancement of electrophilicity of phosphenium cations for the purpose of small-molecule activation was described. Our synthetic methodology for generation of novel two-coordinate phosphorus­(III)-based compounds [{C₆H₄(MeN)₂C}₂C·PR]²⁺ ([<b>2a</b>]²⁺, R = NⁱPr₂; [<b>2b</b>]²⁺, R = Ph) was based on the exceptional electron-donating properties of the carbodicarbene ligand (CDC). The effects of P-centered substituent exchange and increase in the overall positive charge on small substrate activation were comparatively determined by incorporating the bis­(amino)­phosphenium ion [(ⁱPr₂N)₂P]⁺ ([<b>1</b>]⁺) in this study. Implemented structural and electronic modifications of phosphenium salts were computationally verified and subsequently confirmed by isolation and characterization of the corresponding E–H (E = B, Si, C) bond activation products. While both phosphenium mono- and dications oxidatively inserted/cleaved the B–H bond of Lewis base stabilized boranes, the increased electrophilicity of doubly charged species also afforded the activation of significantly less hydridic Si–H and C–H bonds. The preference of [<b>2a</b>]²⁺ and [<b>2b</b>]²⁺ to abstract the hydride rather than to insert into the corresponding bond of silanes, as well as the formation of the carbodicarbene-stabilized parent phosphenium ion [{C₆H₄(MeN)₂C}₂C·PH₂]⁺ ([<b>2</b>·<b>PH</b>_<b>2</b>]⁺) were experimentally validated