The present invention is based on the discovery that certain transition metal containing complexes thermally decompose to form solids containing the transition metal, sulfur and carbon and that these transition metal, sulfur and carbon containing solids are particularly suitable as catalysts for hydrodesulfurization, hydrodenitrogenation and aromatics hydrogenation. The transition metal complexes that are thermally decomposed to novel catalysts are complexes of the type represented by the general formula ML.sup.n 3, wherein M is selected from Mo, W, Re and mixtures thereof, L is a dithiolene or aminobenzenethiolate ligand, and n represents the total charge of the metal complexes, and is 0, -1, or -2.