Whaley C Matthew, Rauchfuss Thomas B, Wilson Scott R
Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
Inorg Chem. 2009 May 18;48(10):4462-9. doi: 10.1021/ic900200s.
The photoreaction of Fe(CO)(5) and cyanide salts in MeCN solution affords the dianion Fe(CN)(2)(CO)(3), conveniently isolated as K(18-crown-6)[Fe(CN)(2)(CO)(3)]. Solutions of Fe(CN)(2)(CO)(3) oxidize irreversibly at -600 mV (vs Ag/AgCl) 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 pK(a) approximately 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)(2)L (L = P(OPh)(3) and PPh(3)). Carbonyl substitution on 1H(CO)(2) by P(OPh)(3) is first-order in both the phosphite and iron (k = 0.18 M(-1) s(-1) at 22 degrees C) with DeltaH(double dagger) = 51.6 kJ mol(-1) and DeltaS(double dagger) = -83.0 J K(-1) mol(-1). These ligands are displaced under an atmosphere of CO. With cis-Ph(2)PCH=CHPPh(2) (dppv), we obtained the monocarbonyl, HFe(CN)(2)(CO)(dppv), a highly basic hydride (pK(a) > 23.3) that rearranges in solution to a single isomer. Treatment of [K(18-crown-6)][HFe(CN)(2)(CO)(3)] with Et(4)NCN resulted in rapid deprotonation to give Fe(CN)(2)(CO)(3) and HCN. The tricyano hydride HFe(CN)(3)(CO)(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) 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(18-crown-6)[Fe(CN)(2)(CO)(3)] with MeOTf gives the thermally unstable MeFe(CN)(2)(CO)(3), which was characterized spectroscopically at -40 degrees 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) undergoes protonation and methylation at Fe, acid chlorides give the iron(0) N-acylisocyanides Fe(CN)(CO)(3)(CNCOR) (R = Ph, CH(3)). The solid state structures of [K(18-crown-6)][HFe(CN)(2)(CO)(dppv)], Fe(CN)(2)(NCMe)(CO)(dppv), and K(18-crown-6)[HFe(CN)(3)(CO)(2)] were confirmed crystallographically. In all three cases, the cyanide ligands are cis to the hydride or acetonitrile ligands.
五羰基铁（Fe(CO)₅）与氰化物盐在乙腈溶液中的光反应生成二价阴离子[Fe(CN)₂(CO)₃]²⁻，可方便地以[K(18 - 冠 - 6)]₂[Fe(CN)₂(CO)₃]的形式分离出来。[Fe(CN)₂(CO)₃]²⁻溶液在 - 600 mV（相对于Ag/AgCl）时不可逆氧化，主要生成[Fe(CN)₃(CO)₃]⁻。该二价阴离子质子化得到氢化物[K(18 - 冠 - 6)][HFe(CN)₂(CO)₃]，其pKa约为17（乙腈）。亚铁氢化物与其抗取代的二价阴离子前体相比，亲电性增强。用叔膦和亚磷酸酯处理[K(18 - 冠 - 6)][Fe(CN)₂(CO)₃]得到[HFe(CN)₂(CO)₂L]⁻（L = P(OPh)₃和PPh₃）的异构体混合物。亚磷酸酯P(OPh)₃对[HFe(CO)₂]⁻的羰基取代反应对亚磷酸酯和铁均为一级反应（22℃时k = 0.18 M⁻¹ s⁻¹），活化焓ΔH⁺ = 51.6 kJ mol⁻¹，活化熵ΔS⁺ = - 83.0 J K⁻¹ mol⁻¹。这些配体在CO气氛下被取代。用顺式 - Ph₂PCH = CHPPh₂（dppv）反应，得到单羰基化合物[HFe(CN)₂(CO)(dppv)]⁻，它是一种高碱性氢化物（pKa > 23.3），在溶液中重排为单一异构体。用Et₄NCN处理[K(18 - 冠 - 6)][HFe(CN)₂(CO)₃]导致快速去质子化，生成[Fe(CN)₂(CO)₃]²⁻和HCN。三氰基氢化物[HFe(CN)₃(CO)₂]²⁻通过[HFe(CN)₂(CO)₂(PPh₃)]⁻与[K(18 - 冠 - 6)]CN反应制备。与膦和亚磷酸酯衍生物类似，[HFe(CN)₃(CO)₂]²⁻以所有三种可能异构体的混合物形式存在。乙腈溶液中[HFe(CN)₂(CO)(dppv)]⁻和[HFe(CN)₃(CO)₂]⁻质子化释放H₂，并生成相应的乙腈配合物[K(18 - 冠 - 6)][Fe(CN)₃(NCMe)(CO)₂]和Fe(CN)₂(NCMe)(CO)(dppv)。用MeOTf对[K(18 - 冠 - 6)]₂[Fe(CN)₂(CO)₃]进行烷基化反应得到热不稳定的[MeFe(CN)₂(CO)₃]⁻，在 - 40℃下通过光谱对其进行了表征。dppv与[MeFe(CN)₂(CO)₃]⁻反应得到乙酰配合物[Fe(CN)₂(COMe)(CO)(dppv)]⁻。虽然[Fe(CN)₂(CO)₃]²⁻在铁原子处发生质子化和甲基化反应，但酰氯会生成铁(0) N - 酰基异氰化物[Fe(CN)(CO)₃(CNCOR)]⁻（R = Ph，CH₃）。通过晶体学确定了[K(18 - 冠 - 6)][HFe(CN)₂(CO)(dppv)]、Fe(CN)₂(NCMe)(CO)(dppv)和[K(18 - 冠 - 6)]₂[HFe(CN)₃(CO)₂]的固态结构。在所有三种情况下，氰化物配体与氢化物或乙腈配体呈顺式。
