Terminal vs bridging hydrides of diiron dithiolates: Protonation of Fe 2(dithiolate)(CO)2(PMe3)4

Riccardo Zaffaroni, Thomas B. Rauchfuss, Danielle L. Gray, Luca De Gioia, Giuseppe Zampella

Research output: Contribution to journalArticlepeer-review


This investigation examines the protonation of diiron dithiolates, exploiting the new family of exceptionally electron-rich complexes Fe 2(xdt)(CO)2(PMe3)4, where xdt is edt (ethanedithiolate, 1), pdt (propanedithiolate, 2), and adt (2-aza-1,3- propanedithiolate, 3), prepared by the photochemical substitution of the corresponding hexacarbonyls. Compounds 1-3 oxidize near -950 mV vs Fc +/0. Crystallographic analyses confirm that 1 and 2 adopt C 2-symmetric structures (Fe-Fe = 2.616 and 2.625 ̊, respectively). Low-temperature protonation of 1 afforded exclusively [μ-H1]+, establishing the non-intermediacy of the terminal hydride ([t-H1]+). At higher temperatures, protonation afforded mainly [t-H1]+. The temperature dependence of the ratio [t-H1] +/[μ-H1]+ indicates that the barriers for the two protonation pathways differ by ∼4 kcal/mol. Low-temperature 31P{1H} NMR measurements indicate that the protonation of 2 proceeds by an intermediate, proposed to be the S-protonated dithiolate [Fe2(Hpdt)(CO)2(PMe3)4]+ ([S-H2]+). This intermediate converts to [t-H2]+ and [μ-H2]+ by first-order and second-order processes, respectively. DFT calculations support transient protonation at sulfur and the proposal that the S-protonated species (e.g., [S-H2]+) rearranges to the terminal hydride intramolecularly via a low-energy pathway. Protonation of 3 affords exclusively terminal hydrides, regardless of the acid or conditions, to give [t-H3]+, which isomerizes to [t-H3′]+, wherein all PMe3 ligands are basal.

Original languageEnglish (US)
Pages (from-to)19260-19269
Number of pages10
JournalJournal of the American Chemical Society
Issue number46
StatePublished - Nov 21 2012

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry


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