Ruthenium anchored on multi-walled carbon nanotubes: an efficient and reusable catalyst for the synthesis of xanthenes

A novel and highly efficient ruthenium-based catalyst was synthesized by immobilizing Ru(CO)4 onto functionalized multi-walled carbon nanotubes. The catalyst was characterized by Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray analysis, diffuse reflectance UV–Vis spectrophotometry, inductively coupled plasma and elemental analysis. This heterogeneous catalyst was successfully applied in the multi-component synthesis of various xanthene derivatives in good to excellent yields (28 samples, up to 96 % yield) under reflux condition and ultrasonic irradiation. The prepared catalyst was recovered four times without appreciable loss of activity.