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

Herein, we report the synthesis and characterization of the mixed-valent, ketimide-stabilized Pd-7 nanosheet, [Pd-7(N=(CBu2)-Bu-t)(6)] (1), via reaction of PdCl2(PhCN)(2) and Li(N=(CBu2)-Bu-t). (BuCN)-Bu-t, isobutylene, and isobutane are also formed in the reaction. The presence of these products suggests that Li(N=(CBu2)-Bu-t) 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 [Pd-7](6+) core stabilized by six ketimide ligands, which surround the [Pd-7](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)-Bu-t=N)Pd(mu-N,C-N=C(Bu-t)C(Me)(CH2)-C-2)Pd(N=(CBu2)-Bu-t)] (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.