Coordination chemistry of [HFe(CN) 2(CO) 3] - and its derivatives: Toward a model for the iron subsite of the [NiFe]-hydrogenases

C. Matthew Whaley, Thomas B. Rauchfuss, Scott R. Wilson

Research output: Contribution to journalArticlepeer-review

Abstract

The photoreaction of Fe(CO)5 and cyanide salts in MeCN solution affords the dianion [Fe(CN) 2(CO) 3] 2-, conveniently isolated as [K(18-crown-6)] 2[Fe(CN) 2(CO) 3], Solutions of [Fe(CN) 2(CO) 3] 2- oxidize irreversibly at -600 mV (vs Ag/ AgCI) to give primarily [Fe(CN) 3(CO) 3]-. Protonation of the dianion affords the hydride [K(18-crown-6)][HFe(CN) 2(CO) 3] with a pKa % 17 (MeCN). The ferrous hydride exhibits enhanced electrophilicity vs its dianionic precursor, which resists substitution. Treatment of [K(18-crown-6)][Fe(CN) 2(CO) 3] with tertiary phosphines and phosphites gives isomeric mixtures of [HFe(CN) 2(CO) 2L]- (L = P(OPh)3 and PPh3). Carbonyl substitution on [1H(CO) 2]- by P(OPh) 3 is firstorder in both the phosphite and iron (k = 0.18 M-1 s-1 at 22 °C) with ΔH = 51.6 kJ mol-1 and ΔS= -83.0 J K-1 mol-1. These ligands are displaced under an atmosphere of CO. With CZs-Ph2PCH=CHPPh2 (dppv), we obtained the monocarbonyl, [HFe(CN) 2(CO)(dppv)]-, a highly basic hydride (pZCa > 23.3) that rearranges in solution to a single isomer. Treatment of [K(18-crown-6)][HFe(CN) 2(CO) 3] with Et4NCN resulted in rapid deprotonation to give [Fe(CN) 2(CO) 3] 2- and HCN. The tricyano hydride [HFe(CN) 3(CO) 2] 2- is prepared by the reaction of [HFe(CN) 2(CO) 2(PPh 3)] - and [K(18-crown-6)]CN. Similar to the phosphine and phosphite derivatives, [HFe(CN) 3(CO) 2] 2- exists as a mixture of all three possible isomers. Protonation of the hydrides [HFe(CN) 2(CO)(dppv)]- and [HFe(CN) 3(CO) 2]- in acetonitrile solutions releases H 2 and gives the corresponding acetonitrile complexes [K(18-crown-6)][Fe(CN) 3(NCMe)(CO) 2] and Fe(CN) 2(NCMe)(CO)(dppv). Alkylation of [K(18crown-6)] 2[Fe(CN) 2(CO) 3] with MeOTf gives the thermally unstable [MeFe(CN)2(CO)3]-, which was characterized spectroscopically at -40°C. Reaction of dppv with [MeFe(CN) 2(CO) 3]- gives the acetyl complex, [Fe(CN) 2(COMe)(CO)(dppv)]-. Whereas [Fe(CN) 2(CO) 3] 2- undergoes protonation and methylation at Fe, acid chlorides give the iron(O) /V-acylisocyanides [Fe(CN)(CO) 3(CNCOR)]- (R = Ph, CH 3). The solid state structures of [K(18crown-6)][HFe(CN) 2(CO)(dppv)], Fe(CN) 2(NCMe)(CO) (dppv), and [K(18-crown-6)] 2[HFe(CN) 3(CO) 2] were confirmed crystallographically. In all three cases, the cyanide ligands are cis to the hydride or acetonitrile ligands.

Original languageEnglish (US)
Pages (from-to)4462-4469
Number of pages8
JournalInorganic Chemistry
Volume48
Issue number10
DOIs
StatePublished - May 18 2009

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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