Acidic Dicationic Iron(II) Dihydrogen Complexes and Compounds Related by H(2) 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 CD(2)Cl(2). [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 CD(2)Cl(2) with AgSbF(6) under 1 atm of H(2). Complex 3 is more acidic than trifluoromethanesulfonic acid (HOTf) in CD(2)Cl(2), while 6 is suspected to be less acidic than [Et(2)OH](+). 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(H(2)O)(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(-) = [BF(4)](-), 7[BF(4)]; Y(-) = [OTf](-), 8[OTf]) were isolated from the corresponding reactions of [trans-FeH(CO)(depe)(2)]Y with [Et(2)OH][BF(4)] or HOTf. 7[BF(4)] was structurally characterized by single-crystal X-ray diffraction. Attempts to grow crystals of 8[OTf] yielded salts containing the complex [trans-Fe(H(2)O)(CO)(depe)(2)](2+) (9), which were structurally characterized by single-crystal X-ray diffraction. Coordination of [BF(4)](-) in 7[BF(4)] was demonstrated, by variable-temperature (31)P{(1)H} NMR spectroscopy, to be dynamic. Dissolving 7[BF(4)] 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[BF(4)] from the reaction mixture resulted in crystals of [H(2)(depe)][BF(4)], which were structurally characterized by single-crystal X-ray diffraction.