Bimetallic Cobalt鈥揇initrogen Complexes: Impact of the Supporting Metal on N2 Activation

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• 作者：Laura J. Clouston ; Varinia Bernales ; Rebecca K. Carlson ; Laura Gagliardi ; Connie C. Lu
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：October 5, 2015
• 年：2015
• 卷：54
• 期：19
• 页码：9263-9270
• 全文大小：475K
• ISSN：1520-510X

文摘

Expanding a family of cobalt bimetallic complexes, we report the synthesis of the Ti(III) metalloligand, Ti[N(o-(NCH₂P(ⁱPr)₂)C₆H₄)₃] (abbreviated as TiL), and three heterobimetallics that pair cobalt with an early transition metal ion: CoTiL (1), K(crypt-222)[(N₂)CoVL] (2), and K(crypt-222)[(N₂)CoCrL] (3). The latter two complexes, along with previously reported K(crypt-222)[(N₂)CoAlL] and K(crypt-222)[(N₂)Co₂L], constitute an isostructural series of cobalt bimetallics that bind dinitrogen in an end-on fashion, i.e. [(N₂)CoML]^{鈭?/sup>. The characterization of 1鈥?b>3 includes cyclic voltammetry, X-ray crystallography, and infrared spectroscopy. The [CoTiL]0/鈥?/sup> reduction potential is extremely negative at 鈭?.20 V versus Fc+/Fc. In the CoML series where M is a transition metal, the reduction potentials shift anodically as M is varied across the first-row period. Among the [(N₂)CoML]鈭?/sup> compounds, the dinitrogen ligand is weakly activated, as evidenced by N鈥揘 bond lengths between 1.110(8) and 1.135(4) 脜 and by N鈥揘 stretching frequencies between 1971 and 1995 cm鈥?. Though changes in 谓_N2 are subtle, the extent of N₂ activation decreases across the first-row period. A correlation is found between the [CoML]0/鈥?/sup> reduction potentials and N₂ activation, where the more cathodic potentials correspond to lower N鈥揘 frequencies. Theoretical calculations of the [(N₂)CoML]鈭?/sup> complexes reveal important variations in the electronic structure and Co鈥揗 interactions, which depend on the exact nature of the supporting metal ion, M.}