Guided ion beam mass spectrometry has been used to examine the kinetic energy dependence of reactions of FeL(+) (L = CO and H2O) with D-2. Activation of the D-2 bond by the ligated metal ions is observed. Thresholds for these processes are measured and converted to the following LFe(+)-D bond dissociation energies (BDEs) : D-0(OCFe+-D) = 1.35 +/- 0.08 eV and D-0(H2OFe+-D) = 2.26 +/- 0.12 eV. Comparison of these values to the previously determined D-0(Fe+-D) = 2.16 +/- 0.06 eV permits a quantitative assessment of the effects of ligation on sigma-bond activation by metal complexes. Differences in the abilities of the two FeL(+) species to activate D-2 and to bond to a deuterium atom are rationalized in terms of the electronic structure at the ligated metal ion center.