Fine-Tuning the Energy Barrier for Metal-Mediated Dinitrogen N鈮 Bond Cleavage

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• 作者：Andrew J. Keane ; Brendan L. Yonke ; Masakazu Hirotsu ; Peter Y. Zavalij ; Lawrence R. Sita
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：July 16, 2014
• 年：2014
• 卷：136
• 期：28
• 页码：9906-9909
• 全文大小：314K
• ISSN：1520-5126

文摘

Experimental data support a mechanism for N鈮 bond cleavage within a series of group 5 bimetallic dinitrogen complexes of general formula, {Cp*M[N(ⁱPr)C(R)N(ⁱPr)]}₂(渭-N₂) (Cp* = 畏⁵-C₅Me₅) (M = Nb, Ta), that proceeds in solution through an intramolecular 鈥渆nd-on-bridged鈥?(渭-畏¹:畏¹-N₂) to 鈥渟ide-on-bridged鈥?(渭-畏²:畏²-N₂) isomerization process to quantitatively provide the corresponding bimetallic bis(渭-nitrido) complexes, {Cp*M[N(ⁱPr)C(R)N(ⁱPr)](渭-N)}₂. It is further demonstrated that subtle changes in the steric and electronic features of the distal R-substituent, where R = Me, Ph and NMe₂, can serve to modulate the magnitude of the free energy barrier height for N鈮 bond cleavage as assessed by kinetic studies and experimentally derived activation parameters. The origin of the contrasting kinetic stability of the first-row congener, {Cp*V[N(ⁱPr)C(Me)N(ⁱPr)]}₂(渭-畏¹:畏¹-N₂) toward N鈮 bond cleavage is rationalized in terms of a ground-state electronic structure that favors a significantly less-reduced 渭-N₂ fragment.