Pushing the Limits of Delta Bonding in Metal鈥揅hromium Complexes with Redox Changes and Metal Swapping

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• 作者：Reed J. Eisenhart ; P. Alex Rudd ; Nora Planas ; David W. Boyce ; Rebecca K. Carlson ; William B. Tolman ; Eckhard Bill ; Laura Gagliardi ; Connie C. Lu
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：August 3, 2015
• 年：2015
• 卷：54
• 期：15
• 页码：7579-7592
• 全文大小：679K
• ISSN：1520-510X

文摘

Into the metalloligand Cr[N(o-(NCH₂P(p>ip>Pr)₂)C₆H₄)₃] (1, CrL) was inserted a second chromium atom to generate the dichromium complex Cr₂L (2), which is a homobimetallic analogue of the known MCrL complexes, where M is manganese (3) or iron (4). The cationic and anionic counterparts, [MCrL]p>+p> and [MCrL]p>鈭?/sup>, respectively, were targeted, and each MCr pair was isolated in at least one other redox state. The solid-state structures of the [MCrL]p>+,0,鈥?/sup> redox members are essentially the same, with ultrashort metal鈥搈etal bonds between 1.96 and 1.74 脜. The formal shortness ratios (r) of these interactions are between 0.84 and 0.74 and are interpreted as triple to quintuple metal鈥搈etal bonds with the aid of theory. The trio of (d鈥揹)p>10p> species [Cr₂L]p>鈭?/sup> (2p>redp>), MnCrL (3), and [FeCrL]p>+p> (4p>oxp>) are S = 0 diamagnets. On the basis of M鈥擟r bond distances and theoretical calculations, the strength of the metal鈥搈etal bond across the (d鈥揹)p>10p> series increases in the order Fe < Mn < Cr. The methylene protons in the ligand are shifted downfield in the p>1p>H NMR spectra, and the diamagnetic anisotropy of the metal鈥搈etal bond was calculated as 鈭?500 脳 10p>鈥?6p>, 鈭?900 脳 10p>鈥?6p>, and 鈭?800 脳 10p>鈥?6p> mp>3p> moleculep>鈥?p> for 2p>redp>, 3, and 4p>oxp> respectively. The magnitude of diamagnetic anisotropy is, thus, affected more by bond polarity than by bond order. A comparative vis鈥揘IR study of quintuply bonded 2p>redp> and 3 revealed a large red shift in the 未p>4p> 鈫?未p>3p>未* transition energy upon swapping from the (Cr₂)p>2+p> to the (MnCr)p>3+p> core. Complex 2p>redp> was further investigated by resonance Raman spectroscopy, and a band at 434 cmp>鈥?p> was assigned as the Cr鈥擟r bond vibration. Finally, 4p>oxp> exhibited a M枚ssbauer doublet with an isomer shift of 0.18 mm/s that suggests a primarily Fe-based oxidation to Fe(I).