Palladium clusters on dicarboxyl-functional hypercrosslinked porous polymers for oxidative homocoupling of benzene with O2

Aryl sulfonate anion stabilized aromatic triangular cation [Pd3]+: syntheses, structures and properties

A series of sulfonate anions paired aromatic triangular palladium clusters 3-7, abbreviated as [Pd3]+[ArSO3]-, were synthesized using a simple "one pot" method, and gave excellent isolated yields (90-95%). Their structures and properties have been fully characterized and further investigated by fluorescence, single crystal X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). In varying organic solvents, they presented apparently stronger absorption and emission in MeOH, driven by the combined interactions of hydrogen bonds and polarity. The crystallographic data demonstrated that the methyl orange ion stabilized complex 7 possessed a D3h symmetric metallic core which was still coplanar and almost equilateral, jointly influenced by the giant hindrance and milder donating effect from the sulfonate. The binding energies for Pdn+ 3d5/2 and Pdn+ 3d3/2 measured by XPS presented at 336.55 and 342.00 eV, respectively. These data were much lower than that of a usual Pd2+ 3d and significantly higher than that of a Pd0 species, further proving the unified palladium valence state (+4/3) in the tri-palladium core and its aromaticity featured by the cyclic electron delocalization.

Pd Clusters on Schiff Base–Imidazole-Functionalized MOFs for Highly Efficient Catalytic Suzuki Coupling Reactions

Subnanometer noble metal clusters have attracted much attention because of abundant low-coordinated metal atoms that perform excellent catalytic activity in various catalytic processes. However, the surface free energy of metals increases significantly with decreasing size of the metal clusters, which accelerates the aggregation of small clusters. In this work, new Schiff base–imidazole-functionalized MOFs were successfully synthesized via the postsynthetic modification method. Highly dispersed Pd clusters with an average size of 1.5 nm were constructed on this functional MOFs and behaved excellent catalytic activity in the Suzuki coupling of phenyboronic acid and bromobenzene (yield of biaryl >99%) under mild reaction conditions. Moreover, the catalyst can be reused six times without loss of activity. Such catalytic behavior is found to closely related to the surface functional groups that promote the formation of small Pd⁰ clusters in the metallic state.