Evidence for the Formation of Terminal Hydrides by Protonation of an Asymmetric Iron Hydrogenase Active Site Mimic

Abstract

Treatment of [Fe2(mu-pdt)(CO)6] [pdt=S(CH2)3S] with dppe (Ph2PCH2CH2PPh2) in refluxing toluene affords the asymmetric complex [Fe2(mu-pdt)(CO)4(dppe)] (1). Protonation of 1 with HBF4-Et2O in CH2Cl2 gives at room temperature the mu-hydrido derivative [Fe2(mu-pdt)(CO)4(dppe)(mu-H)](BF4) (2). Monitoring the reaction by 1H, 31P, and 13C NMR at low temperature reveals unambiguously that the process of the protonation of 1 implies terminal hydride intermediates.

Unsaturated, Mixed‐Valence Diiron Dithiolate Model for the Hox State of the [FeFe] Hydrogenase

“…[Fe 2 (S 2 C 2 H 4 )(CO) 3 Synthesis and reactions of [Fe 2 (S 2 C 2 H 4 )(CO) 3 (PMe 3 )(dppv)] + .…”

“…[2] Research in this area is aimed at elucidating the mechanism of the enzymatic catalysis and at using this information to develop protein-free bioinspired synthetic catalysts. [3] A specific research goal is the preparation of molecules that resemble the functional states of the active site with the expectation that function will follow form. Most studies on diiron dithiolato carbonyl complexes rely on organic ligands (e.g.…”

“…[5] In very recent work, the oxidation of [Fe 2 (S 2 C 3 H 6 )(CO) 4 (PMe 3 )L 1 ] (L 1 =1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) was shown to give a mixed-valence derivative with structural and spectroscopic features resembling H ox . [6] Our recently reported species [Fe 2 (S 2 C 2 H 4 )(CO) 3 (PMe 3 )-(dppv)] (1, dppv =cis-1,2-C 2 H 2 (PPh 2 ) 2 ) is attractive, because, like the active site, this diiron framework bears three donor ligands and three CO ligands. [7] We previously showed that oxidation of 1 in MeCN gives [1 (NCMe) The purple-colored compound 1-BF 4 is stable in solution for several minutes at room temperature and is sufficiently stable that we were able to grow single crystals for X-ray diffraction (see below).…”

Isocyanide in Biochemistry? A Theoretical Investigation of the Electronic Effects and Energetics of Cyanide Ligand Protonation in [FeFe]‐Hydrogenases

“…In fact, the strong interactions between the cyanide and the protein stabilize a disposition of ligands such that a coordination position on the metal center remains vacant, and thus suited for substrate binding. [5,6] Proton attachment to this site can thus lead to the formation of a metastable terminal hydride coordination compound, [7,8] which is highly reactive in terms of H 2 evolution (see Figure 1). [9] However, various kinds of protonation events have been proposed to take place in the enzyme active site.…”

[FeFe] Hydrogenase: Protonation of {2Fe3S} Systems and Formation of Super‐reduced Hydride States

“…[6] Synthetic bridging hydride species at {2Fe2S} cores are structurally well-established [7][8][9] and the chemistry of terminal hydrides at such centers is rapidly developing. [10][11][12][13] Related {2Fe3S} cores have a somewhat closer structural homology to the ironsulfur core of the [FeFe]-hydrogenase subsite. They have provided primary evidence for bridging carbonyl intermediates at Fe I Fe I [14] and Fe I Fe II [15] levels and pathways for the synthesis of free-standing [16] or polymerconfined [17] thiolate-bridged {4Fe4S}-{2Fe3S} assemblies.…”