NiI(1,4,8,11-tetraazacyclotetradecane)+, Ni(I)L+, was produced in neutral aqueous solutions by radiolytic techniques. The mechanism and kinetics of the reaction of Ni(I)L+ with maleate and fumarate were studied applying pulse-radiolysis and analysis of the final products. Surprisingly the mechanisms of reduction of maleate and fumarate differ considerably. Based on the results it was also shown that Ni(II)L2+ is an electrocatalyst for the reduction of alkenes in aqueous solutions.