Preparation, Facile Deprotonation, and Rapid H/D Exchange of the μ-Hydride Diiron Model Complexes of the [FeFe]-Hydrogenase Containing a Pendant Amine in a Chelating Diphosphine Ligand

The CO-displacement of [(mu-pdt)Fe-2(CO)(6)] with (Ph2PCH2)(2)N(n-Pr) in refluxing toluene gave an unsymmetrical chelating complex [(mu-pdt){Fe(CO)(3)}{Fe(CO)(kappa(2)-Ph2PCH2N(n-Pr)CH2PPh2}] (1) as a major product, together with a small amount of the symmetrical intramolecular bridging complex [(mu-pdt){mu-Ph2PCH2N(n-Pr)CH2PPh2}{Fe(CO)(2)}(2)] (2) and the intermolecular bridging complex [{mu,kappa(1),kappa(1)-Ph2PCH2N(n-Pr)CH2PPh2}{(mu-pdt)Fe-2(CO)(5)}(2)] (3). In contrast, the reaction of [(mu-pdt)Fe-2(CO)(6)] with (Ph2PCH2)(2)NR (R=n-Pr, Ph) afforded the intermolecular bridging isomers 3 and 4 in the presence of a CO-removing reagent Me3NO center dot 2H(2)O in CH3CN at room temperature, The molecular structures of 1, 3, and 4, as well as the doubly protonated complex [1(HNH mu)](OTf)(2)] were determined by X-ray analyses. The protonation processes of 1 with HBF4 center dot Et2O and HOTf were studied in different solvents. The presence of the H mu center dot center dot center dot H-N interaction in [1(HNH mu)(2+) was studied by relaxation time T-1 and spin saturation transfer measurements. The mu-hydride of [1(H-mu)](+) and [1(HNH mu)](2+), undergo facile deprotonation with aniline and rapid H/D exchange with deuterons in solution In contrast, neither deprotonation nor H/D exchange was detected for [(mu-H)(mu-pdt){Fe(CO)(3)}{Fe(CO)(kappa(2)-dppp)}](+) ([5(H-mu)](+), dppp=Ph2PCH2CH2CH2PPh2) without internal base.