Acidic dicationic iron(II) dihydrogen complexes and compounds related by H2 substitution

[trans-Fe(H-2)(CO)(dppe)(2)](2+) (3) (dppe = 1,2-bis(diphenylphosphino)ethane) was generated by protonation of [trans-FeH(CO)(dppe)(2)](+) in CD2Cl2. [trans-Fe(H-2)(CO)(depe)(2)](2+) (6) (depe = 1,2-bis(diethylphosphino)ethane) was generated by the treatment of [trans-FeCl(CO)(depe)(2)](+) in CD2Cl2 with AgSbF6 under 1 atm of H-2. Complex 3 is more acidic than trifluoromethanesulfonic acid (HOTf) in CD2Cl2, while 6 is suspected to be less acidic than [Et2OH](+). 3[OTf](2) is stable to H-2 loss under reduced pressure for several hours, an indication of strong three-center (Fe-H-2), two-electron sigma-bonding. Both complexes 3 and 6 undergo H-2 substitution reactions. There is evidence of the formation of [trans-Fe(H2O)(CO)(dppe)(2)](2+) and [trans-Fe(OTf)(CO)(dppe)(2)](+). although these complexes could not be isolated. [trans-FeY(CO)(depe)(2)]Y complexes (Y- = [BF4](-), 7[BF4]; Y- = [OTf](-), 8[OTf]) were isolated from the corresponding reactions of [trans-FeH(CO)(depe)(2)]Y with [Et2OH][BF4] or HOTf. 7[BF4] was structurally characterized by single-crystal X-ray diffraction. Attempts to grow crystals of 8[OTf] yielded salts containing the complex [trans-Fe(H2O)(CO)(depe)(2)](2+) (9), which were structurally characterized by single-crystal X-ray diffraction. Coordination of [BF4](-) in 7[BF4] was demonstrated, by variable-temperature P-31{H-1} NMR spectroscopy, to be dynamic. Dissolving 7[BF4] in methanol results in nucleophilic substitution at B to yield the new complex [trans-FeF(CO)(depe)(2)](+) (10). An attempt to grow crystals of 10[BF4] from the reaction mixture resulted in crystals of [H-2(depe)][BF4], which were structurally characterized by single-crystal X-ray diffraction.