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

摘要

The CO-displacement of [(u-pdt)Fe2(CO)6] with (Ph2PCH2)2N(n-Pr) in refluxing toluene gave an unsymmetrical chelating complex [(u-pdt){Fe(CO)3}{Fe(CO)(k2-Ph2PCH2N(n-Pr)CH2PPh2}] (1) as a major product, together with a small amount of the symmetrical intramolecular bridging complex [(u-pdt){u-Ph2PCH2N(n-Pr)CH2PPh2}{Fe-(CO)2}2] (2) and the intermolecular bridging complex [{u,k1,k1-Ph2PCH2N(n-Pr)CH2PPh2}{(u-pdt)Fe2(CO)5}2](3). In contrast, the reaction of [(u-pdt)Fe2(CO)6] with (Ph2PCH2)2NR (R=n-Pr, Ph) afforded the intermolecular bridging isomers 3 and 4 in the presence of a CO-removing reagent Me3NO 3 2H2O in CH3CN at room temperature.The molecular structures of 1, 3, and 4, as well as the doubly protonated complex [1(HNHu)](OTf)2] were determined by X-ray analyses. The protonation processes of 1 with HBF4 3 Et2O and HOTf were studied in different solvents. The presence of the Hu 3 3 3 HN interaction in [1(HNHu)]2b was studied by relaxation time T1 and spin saturation transfer measurements. The u-hydride of [1(Hu)]b and [1(HNHu)]2b 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 [(i-H)-(u-pdt){Fe(CO)3}{Fe(CO)(k2-dppp)}]b ([5(Hu)]b, dppp=Ph2PCH2CH2CH2PPh2) without internal base.