Exploiting the π‑Acceptor Properties of Carbene-Stabilized Phosphorus Centered Trications [L₃P] ³⁺: Applications in Pt(II) Catalysis

Reaction of tris­(dimethylaminocyclopropenium) substituted phosphine 1 with K₂PtCl₄ afforded the bench stable complex 3 which upon treatment with Ag­[CB₁₁H₆Cl₆] turned out to be an excellent catalyst for the transformation of a variety of ortho-biaryl substituted alkynes into polycyclic homo- and heteroarenes of different size, shape, and curvature through a 6-endo-dig cyclization. This constitutes the first example ever reported of using a P₁-centered trication as ligand in catalysis. The strong π-acceptor character of 1 that derives from its three positive charges substantially increases the intrinsic π-acidity of Pt in complex 1·PtCl₂ and dramatically enhances its ability to activate π-systems toward nucleophilic attack. As a consequence, a remarkable acceleration of the model transformation is observed when compared with other classical π-acceptor ligands such as P­(OPh)₃ or P­(C₆F₅)₃. Moreover, the employment of 1 as ligand also expands the scope of this reaction to previously inaccessible substitution patterns. Kinetic studies and deuterium labeling experiments as well as density functional theory (DFT) calculations were performed in order to explain these findings.