Synthetic and structural studies on [Fe2(SR)2(CN)x (CO)6-x]x- as active site models for Fe-only hydrogenases

F. Gloaguen, J. D. Lawrence, M. Schmidt, S. R. Wilson, T. B. Rauchfuss

Research output: Contribution to journalArticle

Abstract

A series of models for the active site (H-cluster) of the iron-only hydrogenase enzymes (Fe-only H2-ases) were prepared. Treatment of MeCN solutions of Fe2(SR)2(CO)6 with 2 equiv of Et4NCN gave [Fe2(SR)2(CN)2(CO)4]2- compounds. IR spectra of the dicyanides feature four vCO bands between 1965 and 1870 cm-1 and two vCN bands at 2077 and 2033 cm-1. For alkyl derivatives, both diequatorial and axial - equatorial isomers were observed by NMR analysis. Also prepared were a series of dithiolate derivatives (Et4N)2[Fe2(SR)2 (CN)2(CO)4], where (SR)2 = S(CH2)2S, S(CH2)3S. Reaction of Et4NCN with Fe2(S-t-Bu)2--(CO)6 gave initially [Fe2(S-t-Bu)2(CN)2 (CO)4]2-, which comproportionated to give [Fe2(S-t- Bu)2(CN)(CO)5]-. The mechanism of the CN--for-CO substitution was probed as follows: (i) excess CN- with a 1:1 mixture of Fe2(SMe)2(CO)6 and Fe2(SC6H4Me)2(CO)6 gave no mixed thiolates, (ii) treatment of Fe2(S2C3H6)(CO)6 with Me3NO followed by Et4NCN gave (Et4N)[Fe2 (S2C3H6)(CN)(CO)5], which is a well-behaved salt, (iii) treatment of Fe2(S2C3H6)(CO)6 with Et4NCN in the presence of excess PMe3 gave (Et4N)[Fe2 (S2C3H6)(CN)(CO)4 (PMe3)] much more rapidly than the reaction of PMe3 with (Et4N)[Fe2(S2C3H6) (CN)(CO)5], and (iv) a competition experiment showed that Et4NCN reacts with Fe2(S2C3H6)(CO)6 more rapidly than with (Et4N)[Fe2 (S2C3H6)(CN)(CO)5]. Salts of [Fe2(SR)2(CN)2(CO)4]2- (for (SR)2 = (SMe)2 and S2C2H4) and the monocyanides [Fe2(S2C3H6) (CN)(CO)5]- and [Fe2(S-t-Bu)2(CN)(CO)5]- were characterized crystallographically; in each case, the Fe-CO distances were ∼10% shorter than the Fe-CN distances. The oxidation potentials for Fe2(S2C3H6)- (CO)4L2 become milder for L = CO, followed by MeNC, PMe3, and CN-; the range is ∼1.3 V. In water, oxidation of [Fe2(S2C3H6) (CN)2(CO)4]2- occurs irreversibly at -0.12 V (Ag|AgCl) and is coupled to a second oxidation.

Original languageEnglish (US)
Pages (from-to)12518-12527
Number of pages10
JournalJournal of the American Chemical Society
Volume123
Issue number50
DOIs
StatePublished - Dec 19 2001

ASJC Scopus subject areas

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

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