Cationic and Neutral Pd and Pt Pincer Complexes of Phosphinamino-Triazolyl-Pyridine [PN(H)N]: Pincer Ligand-Stabilized Palladium Nanoparticles and Their Catalytic Annulation of Internal Alkynes to Indenones.

We describe the synthesis of a triazolyl-pyridine-based aminophosphine, -(diphenylphosphaneyl)-6-(1-phenyl)-1-(1,2,3-triazol-4-yl)pyridine-2-amine [2,6-{(PPh)-N(H)(CHN)(CHNCH)}] [, PN(H)N hereafter], and its palladium and platinum complexes and their catalytic application. The reaction of with [M(COD)Cl] (M = Pd or Pt) afforded the cationic complex [(MCl){PN(H)N}-κ-P,N,N]Cl [M = Pd () or Pt ()]. Alternatively, compounds and were also synthesized by treating [2,6-{HN(CHN)(CHNCH)}] () with [M(COD)Cl] (M = Pd or Pt), followed by the addition of stoichiometric amounts of PPhCl and EtN. The neutral, dearomatized complexes [(MCl){PNN}-κ-P,N,N] [M = Pd () or Pt ()] were prepared by the deprotonation of the NH of and with 1 equiv of BuOK. Compounds and were also synthesized stepwise by treating [2,6-{HN(CHN)(CHNCH)}] () with [M(COD)Cl] (M = Pd or Pt) to give intermediate complexes [{MCl}2,6-{NH(CHN)(CHNCH)-κ-N,N}] [M = Pd () or Pt ()], which were subsequently phosphinated. The -generated PNN ligand-stabilized Pd nanoparticles from compound catalyzed the annulation of -bromobenzaldehyde with alkynes to yield indenone derivatives. Mechanistic investigations suggested that the reaction was catalyzed by Pd nanoparticles () generated from compound and proceeded through sequential oxidative addition, alkyne insertion, and reductive elimination steps to produce indanone products.