Connecting [NiFe]- and [FeFe]-Hydrogenases: Mixed-Valence Nickel鈥揑ron Dithiolates with Rotated Structures

详细信息    查看全文

• 作者：David Schilter ; Thomas B. Rauchfuss ; Matthias Stein
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：August 20, 2012
• 年：2012
• 卷：51
• 期：16
• 页码：8931-8941
• 全文大小：436K
• 年卷期：v.51,no.16(August 20, 2012)
• ISSN：1520-510X

文摘

New mixed-valence iron鈥搉ickel 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]BF₄, where dppe = Ph₂PCH₂CH₂PPh₂ and pdt^{2鈥?/sup> = 鈭扴CH₂CH₂CH₂S鈭? with P-donor ligands (L) afforded the substituted derivatives [(dppe)Ni(pdt)Fe(CO)₂L]BF₄ incorporating L = PHCy₂ ([1a]BF₄), PPh(NEt₂)₂ ([1b]BF₄), 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]BF₄, where dcpe = Cy₂PCH₂CH₂PCy₂) 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 鈥渞otated鈥?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鈥揚 bond. The PCy₃ complexes, rare examples of species featuring 鈥渞otated鈥?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 鈥渉ybrid models鈥?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鈥?/sup> dications represent the closest approach to modeling the highly electrophilic Ni鈥揝I_a state. In the case of L = PPh₂ (2-pyridyl), chelation of this ligand accompanies the second oxidation.}