877034-22-5Relevant articles and documents
Synthesis and vibrational spectroscopy of 57Fe-labeled models of [NiFe] hydrogenase: First direct observation of a nickel-iron interaction
Schilter, David,Pelmenschikov, Vladimir,Wang, Hongxin,Meier, Florian,Gee, Leland B.,Yoda, Yoshitaka,Kaupp, Martin,Rauchfuss, Thomas B.,Cramer, Stephen P.
, p. 13469 - 13472 (2014)
A new route to iron carbonyls has enabled synthesis of 57Fe-labeled [NiFe] hydrogenase mimic (OC)357Fe(pdt)Ni(dppe). Its study by nuclear resonance vibrational spectroscopy revealed Ni-57Fe vibrations, as confirmed by calculations. The modes are absent for [(OC)357Fe(pdt)Ni(dppe)]+, which lacks Ni-57Fe bonding, underscoring the utility of the analyses in identifying metal-metal interactions.
Mixed-valence nickel-iron dithiolate models of the [NiFe]-hydrogenase active site
Schilter, David,Nilges, Mark J.,Chakrabarti, Mrinmoy,Lindahl, Paul A.,Rauchfuss, Thomas B.,Stein, Matthias
, p. 2338 - 2348 (2012/04/18)
A series of mixed-valence nickel-iron dithiolates is described. Oxidation of (diphosphine)Ni(dithiolate)Fe(CO)3 complexes 1, 2, and 3 with ferrocenium salts affords the corresponding tricarbonyl cations [(dppe)Ni(pdt)Fe-(CO)3]+ ([1]+), [(dppe)Ni(edt)Fe(CO)3]+ ([2]+)and [(dcpe)Ni(pdt)Fe(CO)3]+ ([3]+), respectively, where dppe = PH2PCH2CH2PPH2, dcpe = Cy2PCH2CH2PCy2, (Cy = cyclohexyl), pdtH2 = HSCH2CH2CH2SH, and edtH 2 = HSCH2CH2SH. The cation [2]+ proved unstable, but the propanedithiolates are robust. IR and EPR spectroscopic measurements indicate that these species exist as Cs-symmetric species. Crystallographic characterization of [3]BF4 shows that Ni is square planar. Interaction of [1]BF4 with P-donor ligands (L)afforded a series of substituted derivatives of type [(dppe)Ni(pdt)Fe(CO) 2L]BF4 for L = P(OPh)3 ([4a]BF4), P(p-C6H4Cl)3 ([4b]BF4), PPH 2(2-py)([4c]BF4), PPH2(OEt)([4d]BF 4), PPh3 ([4e]BF4), PPH2-(o-C 6H4OMe)([4f]BF4), PPH2(o-C 6H4OCH2OMe)([4g]BF4), P(p-tol) 3 ([4h]BF4), P(p-C6H4OMe) 3 ([4i]BF4), and PMePH2 ([4j]BF4). EPR analysis indicates that ethanedithiolate [2]+ exists as a single species at 110 K, whereas the propanedithiolate cations exist as a mixture of two conformers, which are proposed to be related through a flip of the chelate ring. Moessbauer spectra of 1 and oxidized S = 1/2 [4e]BF4 are both consistent with a low-spin Fe(I)state. The hyperfine coupling tensor of [4e]BF4 has a small isotropic component and significant anisotropy. DFT calculations using the BP86, B3LYP, and PBE0 exchange-correlation functionals agree with the structural and spectroscopic data, suggesting that the SOMOs in complexes of the present type are localized in an Fe(I)-centered d(z2)orbital. The DFT calculations allow an assignment of oxidation states of the metals and rationalization of the conformers detected by EPR spectroscopy. Treatment of [1]+ with CN-and compact basic phosphines results in complex reactions. With dppe, [1]+ undergoes quasi-disproportionation to give 1 and the diamagnetic complex [(dppe)Ni(pdt)Fe(CO)2(dppe)] 2+ ([5] 2+), which features square-planar Ni linked to an octahedral Fe center.
Active-site models for the nickel-iron hydrogenases: Effects of ligands on reactivity and catalytic properties
Carroll, Maria E.,Barton, Bryan E.,Gray, Danielle L.,MacK, Amanda E.,Rauchfuss, Thomas B.
, p. 9554 - 9563 (2011/10/31)
Described are new derivatives of the type [HNiFe(SR) 2(diphosphine)(CO)3]+, which feature a Ni(diphosphine) group linked to a Fe(CO)3 group by two bridging thiolate ligands. Previous work had described [HNiFe(pdt)(dppe)(CO) 3]+ ([1H]+) and its activity as a catalyst for the reduction of protons (J. Am. Chem. Soc.2010, 132, 14877). Work described in this paper focuses on the effects on properties of NiFe model complexes of the diphosphine attached to nickel as well as the dithiolate bridge, 1,3-propanedithiolate (pdt) vs 1,2-ethanedithiolate (edt). A new synthetic route to these Ni-Fe dithiolates is described, involving reaction of Ni(SR) 2(diphosphine) with FeI2(CO)4 followed by in situ reduction with cobaltocene. Evidence is presented that this route proceeds via a metastable μ-iodo derivative. Attempted isolation of such species led to the crystallization of NiFe(Me2pdt)(dppe)I2, which features tetrahedral Fe(II) and square planar Ni(II) centers (H 2Me2pdt = 2,2-dimethylpropanedithiol). The new tricarbonyls prepared in this work are NiFe(pdt)(dcpe)(CO)3 (2, dcpe = 1,2-bis(dicyclohexylphosphino)ethane), NiFe(edt)(dppe)(CO)3 (3), and NiFe(edt)(dcpe)(CO)3 (4). Attempted preparation of a phenylthiolate-bridged complex via the FeI2(CO)4 + Ni(SPh)2(dppe) route gave the tetrametallic species [(CO) 2Fe(SPh)2Ni(CO)]2(μ-dppe)2. Crystallographic analysis of the edt-dcpe compund [2H]BF4 and the edt-dppe compound [3H]BF4 verified their close resemblance. Each features pseudo-octahedral Fe and square pyramidal Ni centers. Starting from [3H]BF4 we prepared the PPh3 derivative [HNiFe(edt)(dppe)(PPh3)(CO)2]BF4 ([5H]BF 4), which was obtained as a ～2:1 mixture of unsymmetrical and symmetrical isomers. Acid-base measurements indicate that changing from Ni(dppe) (dppe = Ph2PCH2CH2PPh2) to Ni(dcpe) decreases the acidity of the cationic hydride complexes by 2.5 pK aPhCN units, from ～11 to ～13.5 (previous work showed that substitution at Fe leads to more dramatic effects). The redox potentials are more strongly affected by the change from dppe to dcpe, for example the [2]0/+ couple occurs at E1/2 = -820 for [2]0/+ vs -574 mV (vs Fc+/0) for [1]0/+. Changes in the dithiolate do not affect the acidity or the reduction potentials of the hydrides. The acid-independent rate of reduction of CH 2ClCO2H by [2H]+ is about 50 s-1 (25 °C), twice that of [1H]+. The edt-dppe complex [2H]+ proved to be the most active catalyst, with an acid-independent rate of 300 s-1.
Hydride-containing models for the active site of the nickel-iron hydrogenases
Barton, Bryan E.,Rauchfuss, Thomas B.
, p. 14877 - 14885 (2011/01/05)
The [NiFe]-hydrogenase model complex NiFe(pdt)(dppe)(CO)3 (1) (pdt = 1,3-propanedithiolate) has been efficiently synthesized and found to be robust. This neutral complex sustains protonation to give the first nickel-iron hydride [1H]BF4. One CO ligand in [1H]BF4 is readily substituted by organophosphorus ligands to afford the substituted derivatives [HNiFe(pdt)(dppe)(PR3)(CO)2]BF4, where PR 3 = P(OPh)3 ([2H]BF4); PPh3 ([3H]BF4); PPh2Py ([4H]BF4, where Py = 2-pyridyl). Variable temperature NMR measurements show that the neutral and protonated derivatives are dynamic on the NMR time scale, which partially symmetrizes the phosphine complex. The proposed stereodynamics involve twisting of the Ni(dppe) center, not rotation at the Fe(CO)2(PR3) center. In MeCN solution, 3, which can be prepared by deprotonation of [3H]BF4 with NaOMe, is about 104 stronger base than is 1. X-ray crystallographic analysis of [3H]BF4 revealed a highly unsymmetrical bridging hydride, the Fe-H bond being 0.40 A shorter than the Ni-H distance. Complexes [2H]BF4, [3H]BF4, and [4H]BF4 undergo reductions near -1.46 V vs Fc0/+. For [2H]BF4, this reduction process is reversible, and we assign it as a one-electron process. In the presence of trifluoroacetic acid, proton reduction catalysis coincides with this reductive event. The dependence of i c/ip on the concentration of the acid indicates that H2 evolution entails protonation of a reduced hydride. For [2H] +, [3H]+, and [4H]+, the acid-independent rate constants are 50-75 s-1. For [2H]+ and [3H]+, the overpotentials for H2 evolution are estimated to be 430 mV, whereas the overpotential for the N-protonated pyridinium complex [4H 2]2+ is estimated to be 260 mV. The mechanism of H 2 evolution is proposed to follow an ECEC sequence, where E and C correspond to one-electron reductions and protonations, respectively. On the basis of their values for its pKa and redox potentials, the room temperature values of ΔGH? and ΔGH- are estimated as respectively as 57 and 79 kcal/mol for [1H]+.
