TY - JOUR
T1 - Connecting [NiFe]- and [FeFe]-hydrogenases
T2 - Mixed-valence nickel-iron dithiolates with rotated structures
AU - Schilter, David
AU - Rauchfuss, Thomas B.
AU - Stein, Matthias
PY - 2012/8/20
Y1 - 2012/8/20
N2 - New mixed-valence iron-nickel dithiolates are described that exhibit structures similar to those of mixed-valence diiron dithiolates. The interaction of tricarbonyl salt [(dppe)Ni(pdt)Fe(CO)3]BF4 ([1]BF 4, where dppe = Ph2PCH2CH2PPh 2 and pdt2- = -SCH2CH2CH 2S-) with P-donor ligands (L) afforded the substituted derivatives [(dppe)Ni(pdt)Fe(CO)2L]BF4 incorporating L = PHCy 2 ([1a]BF4), PPh(NEt2)2 ([1b]BF 4), P(NMe2)3 ([1c]BF4), P(i-Pr) 3 ([1d]BF4), and PCy3 ([1e]BF4). The related precursor [(dcpe)Ni(pdt)Fe(CO)3]BF4 ([2]BF 4, where dcpe = Cy2PCH2CH2PCy 2) gave the more electron-rich family of compounds [(dcpe)Ni(pdt)Fe(CO)2L]BF4 for L = PPh2(2- pyridyl) ([2a]BF4), PPh3 ([2b]BF4), and PCy3 ([2c]BF4). For bulky and strongly basic monophosphorus ligands, the salts feature distorted coordination geometries at iron: crystallographic analyses of [1e]BF4 and [2c]BF4 showed that they adopt "rotated" FeI centers, in which PCy3 occupies a basal site and one CO ligand partially bridges the Ni and Fe centers. Like the undistorted mixed-valence derivatives, members of the new class of complexes are described as NiIIFeI (S = 1/2) systems according to electron paramagnetic resonance spectroscopy, although with attenuated 31P hyperfine interactions. Density functional theory calculations using the BP86, B3LYP, and PBE0 exchange-correlation functionals agree with the structural and spectroscopic data, suggesting that the spin for [1e]+ is mostly localized in a FeI-centered d(z2) orbital, orthogonal to the Fe-P bond. The PCy3 complexes, rare examples of species featuring "rotated" Fe centers, both structurally and spectroscopically incorporate features from homobimetallic mixed-valence diiron dithiolates. Also, when the NiS2Fe core of the [NiFe]-hydrogenase active site is reproduced, the "hybrid models" incorporate key features of the two major classes of hydrogenase. Furthermore, cyclic voltammetry experiments suggest that the highly basic phosphine ligands enable a second oxidation corresponding to the couple [(dxpe)Ni(pdt)Fe(CO)2L]+/2+. The resulting unsaturated 32e- dications represent the closest approach to modeling the highly electrophilic Ni-SIa state. In the case of L = PPh2 (2-pyridyl), chelation of this ligand accompanies the second oxidation.
AB - New mixed-valence iron-nickel dithiolates are described that exhibit structures similar to those of mixed-valence diiron dithiolates. The interaction of tricarbonyl salt [(dppe)Ni(pdt)Fe(CO)3]BF4 ([1]BF 4, where dppe = Ph2PCH2CH2PPh 2 and pdt2- = -SCH2CH2CH 2S-) with P-donor ligands (L) afforded the substituted derivatives [(dppe)Ni(pdt)Fe(CO)2L]BF4 incorporating L = PHCy 2 ([1a]BF4), PPh(NEt2)2 ([1b]BF 4), P(NMe2)3 ([1c]BF4), P(i-Pr) 3 ([1d]BF4), and PCy3 ([1e]BF4). The related precursor [(dcpe)Ni(pdt)Fe(CO)3]BF4 ([2]BF 4, where dcpe = Cy2PCH2CH2PCy 2) gave the more electron-rich family of compounds [(dcpe)Ni(pdt)Fe(CO)2L]BF4 for L = PPh2(2- pyridyl) ([2a]BF4), PPh3 ([2b]BF4), and PCy3 ([2c]BF4). For bulky and strongly basic monophosphorus ligands, the salts feature distorted coordination geometries at iron: crystallographic analyses of [1e]BF4 and [2c]BF4 showed that they adopt "rotated" FeI centers, in which PCy3 occupies a basal site and one CO ligand partially bridges the Ni and Fe centers. Like the undistorted mixed-valence derivatives, members of the new class of complexes are described as NiIIFeI (S = 1/2) systems according to electron paramagnetic resonance spectroscopy, although with attenuated 31P hyperfine interactions. Density functional theory calculations using the BP86, B3LYP, and PBE0 exchange-correlation functionals agree with the structural and spectroscopic data, suggesting that the spin for [1e]+ is mostly localized in a FeI-centered d(z2) orbital, orthogonal to the Fe-P bond. The PCy3 complexes, rare examples of species featuring "rotated" Fe centers, both structurally and spectroscopically incorporate features from homobimetallic mixed-valence diiron dithiolates. Also, when the NiS2Fe core of the [NiFe]-hydrogenase active site is reproduced, the "hybrid models" incorporate key features of the two major classes of hydrogenase. Furthermore, cyclic voltammetry experiments suggest that the highly basic phosphine ligands enable a second oxidation corresponding to the couple [(dxpe)Ni(pdt)Fe(CO)2L]+/2+. The resulting unsaturated 32e- dications represent the closest approach to modeling the highly electrophilic Ni-SIa state. In the case of L = PPh2 (2-pyridyl), chelation of this ligand accompanies the second oxidation.
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U2 - 10.1021/ic300910r
DO - 10.1021/ic300910r
M3 - Article
C2 - 22838645
AN - SCOPUS:84865227636
SN - 0020-1669
VL - 51
SP - 8931
EP - 8941
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 16
ER -