Unsymmetrical Chelation of N-Thioether-Functionalized Bis(diphenylphosphino)amine-Type Ligands and Substituent Effects on the Nuclearity of Iron(II) Complexes: Structures, Magnetism, and Bonding

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• 作者：Christophe Fliedel ; Vitor Rosa ; Andr茅s Falceto ; Patrick Rosa ; Santiago Alvarez ; Pierre Braunstein
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：July 6, 2015
• 年：2015
• 卷：54
• 期：13
• 页码：6547-6559
• 全文大小：612K
• ISSN：1520-510X

文摘

Starting from the short-bite ligands N-thioether-functionalized bis(diphenylphosphino)amine-type (Ph₂P)₂N(CH₂)₃SMe (1) and (Ph₂P)₂N(p-C₆H₄)SMe (2), the Fe(II) complexes [FeCl2(1)]_n (3), [FeCl₂(2)]₂ (4), [Fe(OAc)(1)₂]PF₆ (5), and [Fe(OAc)(2)₂]PF₆ (6) were synthesized and characterized by Fourier transform IR, mass spectrometry, elemental analysis, and also by X-ray diffraction for 3, 4, and 6. Complex 3 is a coordination polymer in which 1 acts as a P,P-pseudochelate and a (P,P),S-bridge, whereas 4 has a chlorido-bridged dinuclear structure in which 2 acts only as a P,P-pseudochelate. Since these complexes were obtained under strictly similar synthetic and crystallization conditions, these unexpected differences were ascribed to the different spacer between the nitrogen atom and the 鈭扴Me group. In both compounds, one Fe鈥揚 bond was found to be unusually long, and a theoretical analysis was performed to unravel the electronic or steric reasons for this difference. Density functional theory calculations were performed for a set of complexes of general formula [FeCl₂(SR₂){R₂¹PN(R²)P鈥睷₂³}] (R = H, Me; R¹, R², and R³ = H, Me, Ph), to understand the reasons for the significant deviation of the iron coordination sphere away from tetrahedral as well as from trigonal bipyramidal and the varying degree of unsymmetry of the two Fe鈥揚 bonds involving pseudochelating PN(R)P ligands. Electronic factors nicely explain the observed structures, and steric reasons were further ruled out by the structural analysis in the solid-state of the bis-chelated complex 6, which displays usual and equivalent Fe鈥揚 bond lengths. Magnetic susceptibility studies were performed to examine how the structural differences between 3 and 4 would affect the interactions between the iron centers, and it was concluded that 3 behaves as an isolated high-spin Fe(II) mononuclear complex, while significant intra- and intermolecular ferromagnetic interactions were evidenced for 4 at low temperatures. Complexes 3 and 4 were also tested in catalytic ethylene oligomerization but did not exhibit any significant activity under the studied conditions.