The reactions of the trans-Fe(DMeOPrPE)(2)Cl-2 complex (I; DMeOPrPE = 1,2-bis(bis(methoxypropyl)phosphino)ethane) and its derivatives were studied in aqueous and nonaqueous solvents with a particular emphasis on the binding and activation of H-2 and N-2. The results show there are distinct differences in the reaction pathways between aqueous and nonaqueous solvents. In water, I immediately reacts to form trans-Fe(DMeOPrPE)(2)(H2O)Cl+. Subsequent reaction with H-2 or N-2 yields trans-Fe(DMeOPrPE)(2)(X-2)Cl+ (X2H2 or N-2). In the case of H-2, further reactivity occurs to ultimately give the trans-Fe(DMeOPrPE)(2)(H-2)H+ product (III). The pathway for the reaction I -> III was spectroscopically examined: following the initial loss of chloride and replacement with H-2, heterolysis of the H-2 ligand occurs to form Fe(DMeOPrPE)(2)(H)Cl; substitution of the remaining chloride ligand by another H-2 molecule then occurs to produce trans-Fe(DMeOPrPE)(2)(H-2)H+. In the absence of H-2 or N-2, trans-Fe(DMeOPrPE)(2)(H2O)Cl+ slowly reacts in water to form Fe(DMeOPrPE)(3)(2+), II. Experiments showed that this species forms by reaction of free DMeOPrPE ligand with trans-Fe(DMeOPrPE)(2)(H2O)Cl+, where the free DMeOPrPE ligand comes from dissociation from the trans-Fe(DMeOPrPE)(2)(H2O)Cl+ complex. In nonaqueous solvents, the chloride ligand in I is not labile, and a reaction with H-2 only occurs if a chloride abstracting reagent is present. Complex III is a useful synthon for the formation of other water-soluble metal hydrides. For example, the trans-[Fe(DMeOPrPE)(2)H(N-2)](+) complex was generated in H2O by substitution of N-2 for the H-2 ligand in III. The trans-Fe(DHBuPE)(2)HCl complex (DHBuPE = 1,2-bis(bis(hydroxybutyl)phosphino)ethane, another water-solubilizing phosphine) was shown to be a viable absorbent for the separation of N-2 from CH4 in a pressure swing scheme. X-ray crystallographic analysis of II is the first crystal structure report of a homoleptic tris chelate of Fe-II containing bidentate phosphine ligands. The structure reveals severe steric crowding at the Fe center.