Isolation of Homo-/Mixed-Valence Ag12 , Ag29 , and Ag8 Clusters Stabilized by Cyclic Alkyl(amino) Carbene-Anchored Monoanionic Phosphorus Ligand.

Abstract

Silver clusters are attractive candidates for their promising optical properties, and biomedical activities. Herein, we report on the first syntheses and isolation of three homo-/mixed-valence silver nanoclusters (NCs) with Ag12 Cl3 , Ag29 , and Ag8 cores [((cAAC)P)6 Ag12 Cl3 ](OTf)3 (1), [((cAAC)P)6 Ag29 ] (2), and [((cAAC)P)4 Ag8 ] (3) having three-/twofold symmetry, employing cyclic alkyl(amino) carbene (cAAC)-supported phosphinidenide (cAACP- ) as the π-accepting stabilizing ligand. The average diameters of Ag NCs 1, and 2 are approximately 1.6 to 2 nm. The redox non-innocent mono-atomic phosphorus anions (P- ) anchored with cAAC ligands are generated in situ by the reaction of AgOTf with a boryl-phosphaalkene (cAAC)P-B(Ni Pr2 )2 through cleavage of the P-B bond with the help of a triflate anion (OTf- ) as a weak nucleophile. Equivalent number of the (cAAC)P- anions generated in situ are oxidized to produce the corresponding bis-phosphinidene (cAAC)2 P2 leading to the generation of Ag0 ions in solution for the formation of the unprecedented mixed-valence Ag NC 2. Complex 3 is achieved by treating potassium phosphinidenide cAACPK with AgNTf2 . The ligand field and the steric hindrance of the (cAAC)P units play crucial roles in stabilizing complexes 1-3, further providing a three- (1, 2)/two- (3) fold stand. The Ag12 Cl3 NC (1) with a tricationic core [AgI 12 Cl3 ] was found to be diamagnetic, and fluorescent, emitting green light at 563 nm when excited at 400 nm. In contrast, the neutral Ag29 (2) and Ag8 (3) clusters were found to be paramagnetic, and NMR silent showing characteristic EPR signals for Ag0 at room temperature.