The established ability of the Fe(II) bridging hydride species (mu-H)(mu-pdt)[Fe(CO)(2)(PMe3)](2)(+), 1-H+, to take-up and heterolytically activate dihydrogen, resulting in H/D scrambling of H-2/D-2 and H-2/D2O mixtures (Zhao et al. Inorg. Chem. 2002, 41, 3917) has prompted a study of simultaneous alkene/H-2 activation by such [Fe]H(2)ase model complexes. That the required photolysis produced an open site was substantiated by substitution of CO in 1-H+ by CH3CN with formation of structurally characterized {(mu-H)(mu-pdt)[Fe(CO)(2)(PMe3)][Fe(CO)(CH3CN)(PMe3)]}(+)[PF6](-). Under similar photolytic conditions, H/D exchange reactions between D-2 and terminal alkenes (ethylene, propene and 1-butene), but not bulkier alkenes such as 2-butene or cyclohexene, were catalyzed by 1-H+ and the edt (SCH2CH2S) analogue, 2-H+. Substantial regioselectivity for H/D exchange at the internal vinylic hydrogen was observed. The extent to which the olefins were deuterium enriched vs deuterated was catalyst dependent. The stabilizing effect of the binuclear chelating ligands, SCH2CH2CH2S, pdt, and SCH2CH2S, edt, is required for the activity of binuclear catalysts, as the mono-dentate mu-SEt analogue decomposed to inactive products under the photolytic conditions of the catalysis. Reactions of 1 and 2 with EtOSO2CF3 Yielded the S-alkylated products, {(mu-SCH2CH2CH2SEt)-[Fe(CO)(2)(PMe3)](2)}(+)[SO3CF3](-) (1-Et+), and 2-Et+, rather than mu-C2H5 analogues to they-H of 1-H+. The stability and lack of reactivity toward H-2 of 1-Et+ and 2-Et+, indicates they are not on the reaction path of the olefin/D-2 H/D exchange process. A mechanism with olefin binding to an open site created by CO loss and formation of an Fe-(CH2CHDR) intermediate is indicated. A likely role of a binuclear chelate effect is implicated for the unique S-XXX-S cofactor in the active site of [Fe]H(2)ase.