Hydride complexes [FeH(N-N)P-3]BPh4 (1, 2) [N-N = 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen); P = P(OEt)(3), PPh(OEt)(2), and PPh2OEt] were prepared by allowing FeCl2(N-N) to react with phosphite in the presence of NaBH4. The hydrides [FeH(bpy)(2)P]BPh4 (3) [P = P(OEt)(3) and PPh(OEt)(2)] were prepared by reacting the tris(2,2'-bipyridine) [Fe(bpy)(3)]Cl-2.5H(2)O complex with the appropriate phosphite in the presence of NaBH4. The protonation reaction of 1 and 2 with acid was studied and led to thermally unstable (above -20 degreesC) dihydrogen [Fe(eta(2)-H-2)(N-N)P-3](2+) (4, 5) derivatives. The presence of the H-2 ligand is indicated by short T-1min values (3.1-3.6 ms) and by J(HD) measurements (31.2-32.5 Hz) of the partially deuterated derivatives. Carbonyl [Fe(CO)(bpy){P(OEt)(3)}(3)](BPh4)(2) (6) and nitrile [Fe(CH3CN)(N-N)P-3](BPh4)(2) (7,8) [N-N = bpy, phen; P = P(OEt)(3) and PPh(OEt)(2)] complexes were prepared by substituting the H-2 ligand in the eta(2)-H-2 4, 5 derivatives. Aryldiazene complexes [Fe(ArN=NH)(N-N)P-3](BPh4)(2) (9, 10, 11) (Ar = C6H5, 4-CH3C6H4) were also obtained by allowing hydride [FeH(N-N)P-3]BPh4 derivatives to react with aryldiazonium cations in CH2Cl2 at low temperature.