Synthesis, Electronic Structure, and Alkene Hydrosilylation Activity of Terpyridine and Bis(imino)pyridine Iron Dialkyl Complexes

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• 作者：Aaron M. Tondreau ; Crisita Carmen Hojilla Atienza ; Jonathan M. Darmon ; Carsten Milsmann ; Helen M. Hoyt ; Keith J. Weller ; Susan A. Nye ; Kenrick M. Lewis ; Julie Boyer ; Johannes G. P. Delis ; Emil Lobkovsky ; Paul J. Chirik
• 刊名：Organometallics
• 出版年：2012
• 出版时间：July 9, 2012
• 年：2012
• 卷：31
• 期：13
• 页码：4886-4893
• 全文大小：385K
• 年卷期：v.31,no.13(July 9, 2012)
• ISSN：1520-6041

文摘

Iron dialkyl complexes, [N₃]Fe(CH₂SiMe₃)₂, with three different classes of tridentate, nitrogen-based 鈥淸N₃]鈥?ligands, aryl-substituted bis(imino)pyridines, terpyridine, and pyridine bis(oxazoline), have been synthesized and evaluated in the catalytic hydrosilylation of olefins with tertiary silanes. The 2,2鈥?6鈥?2鈥?terpyridine (terpy) complex, (terpy)Fe(CH₂SiMe₃)₂, was prepared either via alkylation of (terpy)FeCl₂ with LiCH₂SiMe₃ or by pyridine displacement from (pyridine)₂Fe(CH₂SiMe₃)₂ by free terpyridine. The aryl-substituted bis(imino)pyridine compounds, (^RPDI)Fe(CH₂SiMe₃)₂ (^RPDI = 2,6-(2,6-R₂-C₆H₃N鈺怌Me)₂C₅H₃N), with smaller 2,6-dialkyl substituents (R = Et, Me) or a 2-ⁱPr substituent (^2-iPrPDI)Fe(CH₂SiMe₃)₂ (^2-iPrPDI = 2,6-(2-ⁱPr-C₆H₄N鈺怌Me)₂C₅H₃N, are effective precursors (0.5 mol %) for the anti-Markovnikov hydrosilylation of 1-octene with (Me₃SiO)₂MeSiH and (EtO)₃SiH over the course of 1 h at 60 掳C. No hydrosilylation activity was observed with Et₃SiH. The most hindered member of the series, (^iPrPDI)Fe(CH₂SiMe₃)₂, and the pyridine bis(oxazoline) iron compound, (R,R)-(^iPrPybox)Fe(CH₂SiMe₃)₂ (^iPrPybox = 2,6-bis[isopropyl-2-oxazolin-2-yl]pyridine), were inactive for the hydrosilylation of 1-octene with all tertiary silanes studied. By contrast, the terpyridine precursor, (terpy)Fe(CH₂SiMe₃)₂, reached >95% conversion at 60 掳C with Et₃SiH and (Me₃SiO)₂MeSiH. In addition, the hydrosilylation of vinylcyclohexene oxide was accomplished in the presence of 1.0 mol % (terpy)Fe(CH₂SiMe₃)₂, demonstrating functional group compatibility unique to this compound that is absent from bis(imino)pyridine iron compounds. The electronic structures of all three classes of iron dialkyl compounds have been evaluated by a combination of X-ray diffraction, magnetochemistry, M枚ssbauer spectroscopy, and density functional theory calculations. All of the compounds are best described as high-spin iron(III) compounds with antiferromagnetic coupling to chelate radical anions.