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

Abstract

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.

Synthesis, Spectroscopy, and Hydrogen/Deuterium Exchange in High-Spin Iron(II) Hydride Complexes

“…36 H/D hydride ligand exchange has also been reported using D 2 /H 2 O for hydrogenases, 37 diiron complexes, 36a,38 other metal complexes, 39 along with D + as a deuterium source. 40 In addition, nitrogenase can exchange D from D 2 O into H 2 , but only does so in the presence of N 2 . 17−19 We suggest that the mechanisms advanced above for hydride/D 2 exchange in 3 should be considered in nitrogenase: specifically, bridging hydride species may play key roles in H 2 /D 2 exchange in the FeMoco cluster.…”

Frontiers, Opportunities, and Challenges in Biochemical and Chemical Catalysis of CO2 Fixation

“…In these exchange reactions, the positioning of the hydride ligand adjacent to the pendant amine is required for both proton/hydride exchange and for catalytic production and oxidation of H 2 . 10,13a,14 Isomerization of the terminal hydride to the thermodynamically more stable bridging hydride 6 results in the cessation of proton/hydride exchange and catalysis.…”

Artificial hydrogenases

“…The amine relay strategy promises also to be applicable to catalysts that operate via μ-hydrides. [28]…”