Electron-Transfer-Catalyzed Rearrangement of Unsymmetrically Substituted Diiron Dithiolate Complexes Related to the Active Site of the [FeFe]-Hydrogenases

Abstract

Novel asymmetrically substituted azadithiolate compounds [Fe2(CO)4(kappa2-dppe){micro-SCH2N(R)CH2S}] (R=iPr, 1a; CH2CH2OCH3, 1b; CH2C6H5, 1c) have been synthesized by treatment of [Fe2(CO)6(micro-adt)] [adt=SCH2N(R)CH2S, with R=iPr, CH2CH2OCH3, CH2C6H5] with dppe (dppe=Ph2PCH2CH2PPh2) in refluxing toluene in the presence of Me3NO. 1a-c have been characterized by single-crystal X-ray diffraction analyses. The electrochemical investigation of 1a-c and of [Fe2(CO)4(kappa2-dppe)(micro-pdt)] (1d) [pdt=S(CH2)3S] in MeCN- and THF-[NBu4][PF6] has demonstrated that the electrochemical reduction of 1a-d gives rise to an Electron-transfer-catalyzed (ETC) isomerization to the symmetrical isomers 2a-d where the dppe ligand bridges the iron centers. Compounds 2a-d were characterized by IR and NMR spectroscopy, elemental analysis, and X-ray crystallography for 2a.

Phosphane‐ and Phosphite‐Substituted Diiron Diselenolato Complexes as Models for [FeFe]‐Hydrogenases

“…These resonances can be assigned to the basal-apical isomer of a diiron complex with a chelating dppe ligand. [32][33][34] Only one diastereoisomer has been observed. The mass spectra of 2-5 show the molecular ion peaks followed by the fragmentation of five CO groups in 2 and 3, and four in 4 and 5.…”

“…These data are within the same ranges observed for the unsubstituted [38] complex and for the sulfur analogues. [26,[31][32][33] The molecular structures of 2-6 were determined and are shown in Figures 1, 2, 3, 4, and 5, respectively. The coordination geometry around the iron cores in all complexes are similar to those in its sulfur analogues.…”

Electrochemical Insights into the Mechanisms of Proton Reduction by [Fe2(CO)6{μ‐SCH2N(R)CH2S}] Complexes Related to the [2Fe]H Subsite of [FeFe]Hydrogenase

“…[63] Therefore, the electrochemical reduction of unsymmetrically disubstituted complexes with an azadithiolate bridge in acidic medium might give rise to a proton migration such as that shown in Scheme 9. [64] In contrast to loss of the NH proton, this reaction ensuing the reduction of the N-protonated intermediate (or coupled with it in a CPET process) would lie on the {2 H + /2 e} path since it produces a terminal hydride and restores a protonation site at the N atom.…”

Models of the iron-only hydrogenase: Synthesis and protonation of bridge and chelate complexes [Fe2(CO)4{Ph2P(CH2)nPPh2}(μ-pdt)] (n = 2–4) – evidence for a terminal hydride intermediate

“…Other spectroscopic data were relatively uninformative, the appearance of a singlet at d 60.5 ppm in the 31 P NMR spectrum confirming the symmetric nature of the diiron centre. While this manuscript was in preparation, Schollhammer and co-workers reported the independent synthesis of 4a [7]. This resulted from the electrontransfer-catalysed (ETC) isomerisation of the chelate isomer 3a.…”