A Ketimide-Stabilized Palladium Nanocluster with a Hexagonal Aromatic Pd₇ Core

Herein, we report the synthesis and characterization of the mixed-valent, ketimide-stabilized Pd₇ nanosheet, [Pd₇(N═CBu₂)₆] (1), via reaction of PdCl₂(PhCN)₂ and Li(N═CBu₂). BuCN, isobutylene, and isobutane are also formed in the reaction. The presence of these products suggests that Li(N═CBu₂) acts as a reducing agent in the transformation, converting the Pd(II) starting material into the mixed-valent Pd(I)/Pd(0) product. Complex 1 features a hexagonal planar [Pd₇]⁶⁺ core stabilized by six ketimide ligands, which surround the [Pd₇]⁶⁺ center in an alternating up/down fashion. In situ NMR spectroscopic studies, as well as density functional theory (DFT) calculations, suggest that 1 is formed via the intermediacy of the bimetallic Pd(II) ketimide complex, [(Bu₂C═N)Pd(μ-N,C-N═C(Bu)C(Me)₂CH₂)Pd(N═CBu₂)] (2). DFT calculations also reveal that 1 is a rare example of an all-metal aromatic nanocluster with hexagonal symmetry, sustaining a net diatropic ring-current of 10.6 nA/T, which is similar to that of benzene (11.8 nA/T) or other well-established transition-metal aromatic systems. Finally, we have found that 1 reacts with Ph₃P, cleanly forming the tris-ligated 16-electron Pd(0) phosphine complex, Pd(PPh₃)₃ (3), suggesting that 1 could be a useful precatalyst for a variety of cross-coupling reactions.