Synthesis of Pd(II) complexes of unsymmetrical, hybrid selenoether and telluroether ligands: Isolation of tellura-palladacycles by fine tuning of intramolecular chalcogen bonding in hybrid telluroether ligands

摘要

Two novel unsymmetrical selenoether ligands namely, N,N-dimethyl-2-(o-tolylselanyl)aniline (10) and 2-((2,6-dimethylphenyl)selanyl)-N,N-dimethylaniline (11) were synthesized from N,N-dimethylbenzylamine via the ortho-lithiation route. When ligands 10 and 11 were treated with Pd(COD)Cl-2 (COD = 1,5-cyclooctadiene), the reaction afforded novel Pd(II) complexes of the form Pd(2-NMe2CH2C6H4)(R)SeCl2, where R = 2-MeC6H4(16) and 2,6-MeC6H3(17) respectively. Similarly, when unsymmetrical telluroether ligands, N,N-dimethyl-2-(phenyltellanyl)aniline (12), N,N-dimethyl-2-(otolyltellanyl)aniline (13), 2-((2,6-dimethylphenyl)tellanyl)-N,N-dimethylaniline (14) and 2-((2,6-diisopropylphenyl)tellanyl)-N,N-dimethylaniline (15), which contain one coordinating group with an sp(3) N-donor atom, were treated with Pd(COD)Cl-2, the palladium telluroether complexes of the form Pd(2-NMe2CH2C6H4)(R)TeCl2, where R = C6H5(18), 2-MeC6H4(19), 2,6-MeC6H3(20) and 2,6-(PrC6H3)-Pr-i(21) respectively were obtained. The selenoether complexes 16 and 17 and telluroether complexes 18, 20 and 21 were characterized by single crystal X-ray diffraction studies. In the asymmetric unit of complex 18, two molecules are present and due to the presence of weak, intermolecular Te center dot center dot center dot Cl interactions, the two molecules exist as symmetrically related dimer. The N-donor substituents, which were involved in intramolecular chalcogen bonding (IChB) with the chalcogen atoms in the free ligand, made six-membered chelating rings in the complexes. Again, when bis(2-phenylazophenyl-C,N')selenide 22 was treated with Pd(COD)Cl-2, it afforded ortho C-H bond activated cyclopalladated complex 24. However, when bis (2-phenylazophenyl-C,N')telluride 23 was treated with Pd(COD)Cl-2, due to strong IChB from two N-donor substituents, the reaction afforded cleaved product, [2-(phenylazo)phenyl-C,N']tellurenyl chloride, 25. All the metal complexes exhibited significant downfield chemical shifts in Se-77/Te-125 NMR spectra as compared to the corresponding free ligands. The downfield shifts in the Se-77/Te-125 NMR signal in the complexes might be attributed to the coordination of the chalcogen atoms to the electropositive Pd(II) center. (C) 2019 Elsevier Ltd. All rights reserved.