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

doi:10.1021/ic900200s

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

Chemistry

Research output: Contribution to journal › Article › peer-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 language	English (US)
Pages (from-to)	4462-4469
Number of pages	8
Journal	Inorganic Chemistry
Volume	48
Issue number	10
DOIs	https://doi.org/10.1021/ic900200s
State	Published - May 18 2009

ASJC Scopus subject areas

Physical and Theoretical Chemistry
Inorganic Chemistry

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@article{6ea650ead4904bf9bcbed0a0088b0300,

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

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.",

author = "Whaley, \{C. Matthew\} and Rauchfuss, \{Thomas B.\} and Wilson, \{Scott R.\}",

year = "2009",

month = may,

day = "18",

doi = "10.1021/ic900200s",

language = "English (US)",

volume = "48",

pages = "4462--4469",

journal = "Inorganic Chemistry",

issn = "0020-1669",

publisher = "American Chemical Society",

number = "10",

}

TY - JOUR

T1 - Coordination chemistry of [HFe(CN) 2(CO) 3] - and its derivatives

T2 - Toward a model for the iron subsite of the [NiFe]-hydrogenases

AU - Whaley, C. Matthew

AU - Rauchfuss, Thomas B.

AU - Wilson, Scott R.

PY - 2009/5/18

Y1 - 2009/5/18

N2 - 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.

AB - 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.

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