C–H and C–C Bond Formation Promoted by Facile κ³/κ² Interconversions in a Hemilabile “Click”-Triazole Scorpionate Platinum System

A series of platinum complexes bearing 3-fold symmetrical “Click”-triazole-based scorpionate ligands (Tt^R) has been prepared. Metalation of these weakly donating ligands results in neutral Pt­(II) complexes that display a κ² coordination mode. Such complexes are susceptible to oxidative addition using a variety of electrophilic alkyl and allyl reagents to generate isolable cationic κ³ Pt­(IV) complexes. Protonation of the κ² precursors results in Pt­(IV) dimethyl hydride cations. Thermolysis of the dimethyl hydride species at 35 °C in the presence of a trapping π-acid ligand initiates reductive elimination of methane and formation of a Pt­(II) species of the type [Tt^PhPtMe­(L)]­[BF₄] (L  CO, ethylene, propylene, <i>cis</i>-2-butene, <i>trans</i>-2-butene, isobutylene) in good yield. Furthermore, the κ³ σ-allyl complexes [Tt^RPt­(Ph)₂(CH₂CHCH₂)]­[I] cleanly undergo C_sp2–C_sp2 reductive coupling to form biphenyl at ambient temperatures. The Tt^R ligand serves as a homofunctional hemilabile ligand and exhibits a lower barrier κ³/κ² interconversion to generate reactive unsaturated five-coordinate complexes than the well-studied Tp′PtMe₂H complex, which requires thermolysis at temperatures above 100 °C