Stabilization of a Cobalt–Cobalt Bond by Two Cyclic Alkyl Amino Carbenes

详细信息    查看全文

• 作者：Kartik Chandra Mondal ; Prinson P. Samuel ; Herbert W. Roesky ; Elena Carl ; Regine Herbst-Irmer ; Dietmar Stalke ; Brigitte Schwederski ; Wolfgang Kaim ; Liviu Ungur ; Liviu F. Chibotaru ; Markus Hermann ; Gernot Frenking
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：February 5, 2014
• 年：2014
• 卷：136
• 期：5
• 页码：1770-1773
• 全文大小：320K
• ISSN：1520-5126

文摘

(Me₂-cAAC:)₂Co₂ (2, where Me₂-cAAC: = cyclic alkyl amino carbene, :C(CH₂)(CMe₂)₂N-2,6-iPr₂C₆H₃)) was synthesized via the reduction of precursor (Me₂-cAAC:Co^II(渭-Cl)Cl)₂ (1) with KC₈. 2 contains two cobalt atoms in the formal oxidation state zero. Magnetic measurement revealed that 2 has a singlet spin ground state S = 0. The cyclic voltammogram of 2 exhibits both one-electron oxidation and reduction, indicating the possible synthesis of stable species containing 2^{鈥⑩€?/b>} and 2^鈥? ions. The latter was synthesized via reduction of 1 with required equivalents of KC₈ and characterized as [(Me₂-cAAC:)₂Co₂]^鈥?OTf^{鈥?/sup> (2鈥?OTf鈥?/b>). Electron paramagnetic resonance spectroscopy of 2鈥? reveals the coupling of the electron spin with 2 equiv 59Co isotopes, leading to a (Co0.5)₂ state. The experimental Co1鈥揅o2 bond distances are 2.6550(6) and 2.4610(6) 脜 for 2 and 2鈥?OTf鈥?/b>, respectively. Theoretical investigation revealed that both 2 and 2鈥?OTf鈥?/b> possess a Co鈥揅o bond with an average value of 2.585 脜. A slight increase of the Co鈥揅o bond length in 2 is more likely to be caused by the strong 蟺-accepting property of cAAC. 2鈥? is only 0.8 kcal/mol higher in energy than the energy minimum. The shortening of the Co鈥揅o bond of 2鈥? is caused by intermolecular interactions.}