Pyridine dicarbanion-bonded Ag₁₃ organometallic nanoclusters: synthesis and on-surface oxidative coupling reaction

Highly reactive organometallic nanoclusters in situ generated in metal-catalyzed reactions are pivotal in the comprehension of catalytic mechanisms. Herein, we develop a two-step synthetic method to achieve three unprecedented aryl dicarbanion-bonded Ag₁₃ nanoclusters by using protective macrocyclic ligands. Firstly, various aryl dicarbanion-Ag₄ cluster intermediates are acquired via a silver-mediated annulation reaction within a macrocyclic ligand. These Ag₄ cluster precursors are released from the surrounding macrocycle by protonation, and further undergo an inter-cluster coupling to generate bipyridine products and low-valence silver atoms. The remaining resurgent diide-Ag₄ clusters assemble with low-valence silver atoms to yield a series of organometallic Ag₁₃ nanoclusters. These Ag₁₃ nanoclusters feature a unique open-shell electronic structure as well as a chiral cluster architecture due to the asymmetric arrangements of surrounding aryl dianion ligands. Furthermore, the pyridyl diide ligands on the surface of the nanocluster further experience an intra-cluster oxidative coupling to produce bipyridine coupling products and large nanoparticles. The coupling reaction-driven cluster-to-cluster transformation is comprehensively tracked by high resolution mass spectroscopy. This work is not only reminiscent of the detailed evolution of cluster species upon the occurrence of coupling reactions, but also reproduces novel inter- and intra-cluster coupling steps at different reaction stages.