2015 Fiscal Year Annual Research Report
ヒドロゲナーゼ活性中心のモデル構築をめざしたニッケルー鉄二核錯体の合成と反応
| Project/Area Number |
15F15035
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| Research Institution | Nagoya University |
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Principal Investigator |
巽 和行 名古屋大学, 物質科学国際研究センター, 教授 (10155096)
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| Co-Investigator(Kenkyū-buntansha) |
BOSE MOUMITA 名古屋大学, 物質科学国際研究センター, 外国人特別研究員
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| Project Period (FY) |
2015-04-24 – 2017-03-31
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| Keywords | Hydrogenase / Iron / Nickel / Bimetallic / Thiolates / Hydride |
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| Outline of Annual Research Achievements |
In the FY 2015,-a number of new heterobimetallic dithiolate-bridged Ni-Fe(carbonyl/cyanide) complexes were synthesized as models of the active site of the [Ni-Fe] hydrogenase in its different states (Ni-L, Ni-R and Ni-SI). The reaction of the Fe(II) thiolato complex [(CO)2(CN)2Fe(pdt)](2-) and [(CO)2(CN)2Fe(ndt)](2-) with Ni(0)(PPh3)4 yielded Fe(II)-Ni(0) complexes [(18-Crown-6)K]2[(CO)(CN)2Fe(μ-pdt)Ni(CO)(PPh3)] (1; pdt = propane- 1,3-dithiolate), [(18-Crown-6)K]2[(CO)(CN)2Fe(μ-ndt)Ni(CO)(PPh3)] (2; ndt = norborane-exo-2,3-dithiolate), respectively.
A similar reaction with Ni(II)-hydride complex Ni(H)(Cl)(PCy3)2 afforded the μ-hydride complex [(18-Crown-6)K][(CN)(CO)2Fe(μ-pdt)(μ-H)Ni(CN)(PCy3)](3). These model complexes were characterized by X-ray crystallography and spectroscopic methods. The Fe centers occupy biologically accurate coordination sphere with Ni-Fe distances ~ 2.5 A for 1, 2 and ~ 2.6 A for 3, which are similar to those of the Ni-L and Ni-R state.of- [Ni-Fe] hydrogenases.
In addition, the nickel dithilato complex [Ni(dadt)] (dadt=N,N′-diethyl-3,7-diazanonane-1,9-dithiolate) was reacted with [Fe(II) (CO)3(CN)2Br](-1) or [Fe(II)(CO)4(I)2] to yield [(CO)2(CN)2Fe(dadt)Ni] (4) and [(CO)3Fe(I) (dadt)Ni][B(Ar(F))4] (5) respectively. Treatment of 5 with ethane thiolate and cyanide further resulted bi-nuclear complex [(CO)3Fe(SEt)(dadt)Ni][B(Ar(F))4] (6) and tri-nuclear complex [(dadt)NiFe(CO)(CN)(dadt)Ni][B(Ar(F)]4] (7), respectively. The Ni-Fe distances of 4-7 are ~ 3.1 A. The oxidation state of Fe(II) and Ni (II) represents the Ni-SI state.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Despite the fragileness and thermal instability of the model complexes of [NiFe] hydrogenase active site in this study, we have been successful to synthesize a series of bimetallic Ni-Fe Complexes. Treatment of the Fe(II) precursor complex [Fe(CO)3(CN)2Br](1-)with dithiolate gave us the iron thiolato complexes .having (CO/CN)ligated such as [(CO)2(CN)2Fe(pdt)](2-) and [(CO)2(CN)2Fe(ndt)](2-) which resulted in the formation of the Fe(II)-Ni(0) complexes 1 and 2 having exact coordinating ligands (CO/CN) as of native enzyme to the Fe center dithiolato bridged to Ni center representing the reduced form of enzyme. These complexes will be the newest synthetic model complexes in the literature in which Fe center occupy the biomimetic exact coordination sphere and Ni center retain tetrahedral geometry as of native Ni-L state. Protonation reactions of those complexes are under progress in revelance to the enzyme functions. The usage of Ni-hydride synthon Ni (H)(Cl)(PCy3)2 with iron (CO/CN) thiolato complex [(CO)2(CN)2Fe(pdt)](2-) delivered us the desired hydride bridged bimetallic [Ni-Fe] complex (3) where Fe coordinated to CO and CN and Ni possesses a distorted tetrahedral geometry as one of the very important intermediate model complex in the catalytic cycle of [Ni-Fe] hydrogenase-termed as Ni-R state. While a model complex having CN ligand protected with lewis acid was reported, this is the first Ni-Fe (CO/CN) complex bearing a hydride bridge.
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| Strategy for Future Research Activity |
The model complexes newly synthesized in this project will be further treated with biologically relevant substrate related to [NiFe] hydrogenase catalysis such as proton, hydride, CO to get insight into the uptake-evolution chemistry of proton and dihydrogen exhibited by the hydrogenase. Ligand exchange reaction at the Fe or/and Ni center will be performed to achieve another number of new complexes having biologically accurate coordination sphere around the metals (Fe having (CN)2(CO) and Ni with thiolate) bearing hydride, retaining the proper geometry as well. The dinuclear complexes will be characterized by X-ray crystallography, spectroscopic (ESI-MS, FT-IR, NMR) and analytical methods New insights into the structural feature will be achieved through proper physicochemical characterization of the newly synthesized complexes.
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