N2 Activation by an Iron Complex with a Strong Electron-Donating Iminophosphorane Ligand

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• 作者：Tatsuya Suzuki ; Yuko Wasada-Tsutsui ; Takahiko Ogawa ; Tomohiko Inomata ; Tomohiro Ozawa ; Yoichi Sakai ; Michael D. Fryzuk ; Hideki Masuda
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：October 5, 2015
• 年：2015
• 卷：54
• 期：19
• 页码：9271-9281
• 全文大小：613K
• ISSN：1520-510X

文摘

A new tridentate cyclopentane-bridged iminophosphorane ligand, N-(2-diisopropylphosphinophenyl)-P,P-diisopropyl-P-(2-(2,6-diisopropylphenylamido)cyclopent-1-enyl)phosphoranimine (NpNP^iPr), was synthesized and used in the preparation of a diiron dinitrogen complex. The reaction of the iron complex FeBr(NpNP^iPr) with KC₈ under dinitrogen yielded the dinuclear dinitrogen Fe complex [Fe(NpNP^iPr)]₂(渭-N₂), which was characterized by X-ray analysis and resonance Raman and NMR spectroscopies. The X-ray analysis revealed a diiron complex bridged by the dinitrogen molecule, with each metal center coordinated by an NpNP^iPr ligand and dinitrogen in a trigonal-monopyramidal geometry. The N鈥揘 bond length is 1.184(6) 脜, and resonance Raman spectra indicate that the N鈥揘 stretching mode 谓(¹⁴N₂/¹⁵N₂) is 1755/1700 cm^鈥?. The magnetic moment of [Fe(NpNP^iPr)]₂(渭-N₂) in benzene-d₆ solution, as measured by ¹H NMR spectroscopy by the Evans method, is 6.91渭_B (S = 3). The M枚ssbauer spectrum at 78 K showed 未 = 0.73 mm/s and 螖E_Q = 1.83 mm/s. These findings suggest that the iron ions are divalent with a high-spin configuration and that the N₂ molecule has (N鈺怤)^{2鈥?/sup> character. Density functional theory calculations performed on [Fe(NpNPiPr)]₂(渭-N₂) also suggested that the iron is in a high-spin divalent state and that the coordinated dinitrogen molecule is effectively activated by 蟺 back-donation from the two iron ions (d蟺) to the dinitrogen molecule (蟺_x* and 蟺_y*). This is supported by cooperation between a large negative charge on the iminophosphorane ligand and strong electron donation and effective orbital overlap between the iron d蟺 orbitals and N₂ 蟺* orbitals supplied by the phosphine ligand.}