Nanostructures often have unusual properties that are linked to their small size. We report here on extraordinary chemical properties associated with the edges of two-dimensional MoS2nanoclusters, which we show to be able to hydrogenate and break up thiophene (C4H4S) molecules. By combining atomically resolved scanning tunnelling microscopy images of single-layer MoS2nanoclusters and density functional theory calculations of the reaction energetics, we show that the chemistry of the MoS2nanoclusters can be associated with one-dimensional metallic states located at the perimeter of the otherwise insulating nanoclusters. The new chemistry identified in this work has significant implications for an important catalytic reaction, since MoS2nanoclusters constitute the basis of hydrotreating catalysts used to clean up sulfur-containing molecules from oil products in the hydrodesulfurization process.