Preparation, facile deprotonation, and rapid H/D exchange of the mu-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 (Ph(2)PCH(2))(2)N(n-Pr) in refluxing toluene gave an unsymmetrical chelating complex [(mu-pdt){Fe(CO)(3)}{Fe(CO)(kappa(2)-Ph(2)PCH(2)N(n-Pr)CH(2)PPh(2)}] (1) as a major product, together with a small amount of the symmetrical intramolecular bridging complex [(mu-pdt){mu-Ph(2)PCH(2)N(n-Pr)CH(2)PPh(2)}{Fe(CO)(2)}(2)] (2) and the intermolecular bridging complex [{mu,kappa(1),kappa(1)-Ph(2)PCH(2)N(n-Pr)CH(2)PPh(2)}{(mu-pdt)Fe(2)(CO)(5)}(2)] (3). In contrast, the reaction of [(mu-pdt)Fe(2)(CO)(6)] with (Ph(2)PCH(2))(2)NR (R = n-Pr, Ph) afforded the intermolecular bridging isomers 3 and 4 in the presence of a CO-removing reagent Me(3)NO.2H(2)O in CH(3)CN at room temperature. The molecular structures of 1, 3, and 4, as well as the doubly protonated complex [1(H(N)H(mu))](OTf)(2)] were determined by X-ray analyses. The protonation processes of 1 with HBF(4).Et(2)O and HOTf were studied in different solvents. The presence of the H(mu)...H(N) interaction in [1(H(N)H(mu))](2+) was studied by relaxation time T(1) and spin saturation transfer measurements. The mu-hydride of [1(H(mu))](+) and [1(H(N)H(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 = Ph(2)PCH(2)CH(2)CH(2)PPh(2)) without internal base.