Palladium complexes of C/Se and N/E (E = Se, Te) ligands, 2-(3,5-dimethylpyrazol-1-yl)phenyl substituted chalcogeno-ethers: Functional group effect on structure and catalytic activity

• Preparation of palladium complexes of nonsymmetrically substituted chalcogeno-ethers.
• Complexes exist as bidentate neutral and tridentate ionic species in solution.
• The latter were exclusively isolated by chloride abstraction with triflate ion.
• Varying substitution of ligands affects catalytic activity and crystal structures.
• Strong donor ability of selenium and substituent enables high catalytic efficiency.

Several tri-dentate ionic monochloro-palladium complexes of the type, [PdCl(NˆEˆN′)][OTf] (3a-c, 3′a, 3′c) and [PdCl(CˆSeˆN′)][OTf] (3d) (where, E = Se, Te; N′ = 2-(3,5-dimethylpyrazol-1-yl)phenyl; N = ethylamine/N, N-dimethylethylamine/picolyl and C = 1-methyl-3-ethyl-2,3-dihydro-1H-imidazol carbene, respectively) were isolated from corresponding dichloro complexes (2a–d, 2′a, 2′c) prepared by reacting PdCl2 with equimolar amount of seleno-ether ligands. Some of the representative ionic complexes were unambiguously analyzed by single crystal X-ray diffraction method, and employed for Suzuki–Miyaura carbon–carbon coupling reactions. The effect of subtle changes in ligands, such as variation in auxiliary donor group or chalcogen atom, on crystal structure and catalytic efficiency has been investigated. For the above mentioned studies, auxiliary donor groups of different donor strength such as amines/pyridyl (N-donor) and imidazole based carbene (C-donor) were introduced in seleno-ether ligands.

Several ionic palladium complexes with tridentate asymmetric selenoether ligands, were isolated from corresponding dichloro complexes which were prepared by reacting PdCl2 with selenoether ligands. The effect of subtle changes such as donor group or chalcogen atom, on crystal structure and catalytic efficiency for carbon–carbon coupling reaction, has been investigated.Figure optionsDownload as PowerPoint slide