Novel saccharinate-bridged palladium complexes for efficient C-O bond activation displaying promising luminescence properties

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 41; no. 13; pp. 3832 - 3842
• Main Authors: Santana, M Dolores, García-Bueno, Rocío, García, Gabriel, Sánchez, Gregorio, García, Joaquín, Kapdi, Anant R, Naik, Minal, Pednekar, Suhas, Pérez, José, García, Luis, Pérez, Eduardo, Serrano, J Luis
• Format: Journal Article
• Language: English
• Published: England 07.04.2012
• Subjects: Activation; Carbon - chemistry; Catalysis; Derivatives; Emission; Ligands; Luminescent Agents - chemistry; Models, Molecular; Molecular Conformation; Organometallic Compounds - chemistry; Oxygen - chemistry; Palladium; Palladium - chemistry; Pyridines; Pyridines - chemistry; Quinoline; Solid state
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c2dt12187e

The synthesis of mono- and dinuclear cyclometallated palladium(II) complexes with deprotonated saccharinate ligands displaying different coordination modes is described. The new compounds were prepared by direct reaction between saccharine and the corresponding hydroxo-complexes [{Pd(μ-OH)(C^N)}(2)] (C^N = 2-(2-pyridyl)phenyl (Phpy) I; = 7,8-benzoquinolyl (Bzq) II), showing a general formula [{Pd(μ-sac)(C^N)}(2)] with saccharinate 1 displaying a bridging -NCO-coordination mode. Bridge splitting with neutral ligands (L = pyridine (py) 2, quinoline (quinol) 3 or acridine (acrid) 4) yielded new mononuclear derivatives with saccharinate acting as an N-monodentated ligand. Structural characterization by X-ray diffraction of complexes I1, I2 and II2 confirmed the proposed formulae. All complexes emit in the solution and solid state at room temperature. Emission features between 640-680 nm in the solid state for complexes I1 and II1 are significantly red-shifted if compared to the emission in solution. These broad emissions are consistent with the simultaneous presence of (3)ππ* and (3)MMLCT transitions indicating the existence of a strong intramolecular Pd-Pd ground state interaction. The dimeric complexes have also shown to catalyze Suzuki-Miyaura cross-coupling of coumaryl tosylate and aryl boronic acids under phosphine-free conditions. Initial studies suggest the involvement of palladium nanoparticles, which has been further investigated using mercury-drop test and poisoning experiments.