Synthesis and characterisation of a RuII([14]aneS4) complex immobilised in MCM-41-type mesoporous silica

Abstract

Ruthenium(II) complexes containing the macrocycle 1,4,8,11-tetrathiacyclotetradecane ([14]aneS₄) and nitrogen-coordinated nitrile ligands were prepared using cis-[Ru(DMSO)₄Cl₂] as the starting material. The first synthetic step consisted of introduction of the thioether ligand to give [Ru([14]aneS₄)(DMSO)Cl]Cl. Substitution of the DMSO ligand by the nitrile ligands NCCH₃ or NC(CH₂)₃Si(OEt)₃ (L) gave the complexes [Ru([14]aneS₄)(L)Cl]X (X = Cl⁻, PF₆⁻). Introduction of the triethoxysilyl ligand allowed the [Ru([14]aneS₄)Cl]⁺ fragment to be tethered to the surface of the ordered mesoporous silica MCM-41 by pore volume impregnation of a solution of the complex in dichloromethane. A high metal loading was achieved (0.56 mmol g⁻¹). Powder XRD and N₂ adsorption studies of the derivatised material indicated that the textural properties of the support were preserved during the grafting experiment and that the channels remained accessible, despite a large reduction in both surface area and pore volume (ca. 50%). IR, UV/VIS, photoluminescence and MAS NMR spectroscopy (¹³C, ²⁹Si) confirmed that the structural integrity of the Ru^II complex was retained during immobilisation, except for loss of ethoxide groups due to the reaction with pendant silanols on the silica surface.