The reactions of ethylene with niobium cluster cations (Nb-n(+), n = 2-13), which are generated by laser vaporization/ionization in a Smalley compact supersonic expansion source, are studied using Fourier transform mass spectrometry. The dependence of the reaction rate, saturation limit, and degree of dehydrogenation on cluster size is investigated. Reaction mechanisms and the nature of the bonding between the metal center and the ligand(s) in the reaction product ions are proposed.