First-Row Transition Metal and Lithium Pyridine-ene-amide Complexes Exhibiting N- and C-Isomers and Ligand-Based Activation of Benzylic C鈥揌 Bonds

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• 作者：Brian M. Lindley ; Peter T. Wolczanski ; Thomas R. Cundari ; Emil B. Lobkovsky
• 刊名：Organometallics
• 出版年：2015
• 出版时间：October 12, 2015
• 年：2015
• 卷：34
• 期：19
• 页码：4656-4668
• 全文大小：980K
• ISSN：1520-6041

文摘

Ene-amines Z-3-(2-pyridyl)-1-aza(2,6-ⁱPr₂-Ph)propene, (pynac)H, and 2-(2-pyridyl)-1-aza(2,6-R,R鈥?Ph)propene, (pyEA-ArRR鈥?H, were synthesized by condensation procedures; corresponding lithium or potassium ene-amides were prepared via standard deprotonation protocols. Addition of 2 equiv of (pynac)H to {(Me₃Si)₂N}₂Fe(THF) or 2 Li(pynac) to FeBr₂(THF)₂ afforded (pynac)₂Fe (1), while treatment of CrCl₂(THF)₂, MnCl₂, FeBr₂(THF)₂, and CoCl₂py₄ with 2 equiv of (pyEA-ArⁱPr₂)K afforded pseudotetrahedral (pyEA-ArⁱPr₂)₂M (2-M, M = Cr, Mn, Fe) and (pyEA-ArⁱPr₂)₂Co-py (2-Co-py). Diamagnetic (魏-C,N-pyEA-ArⁱPr₂)₃Co (3) was prepared in low yield (鈭?%) from CoCl₂, and its Co鈥揅(sp³) linkages are unusually low in field strength. Reactivity studies yielded little clean reactivity, but thermolysis of 2-Co-py afforded the bis-indolamide derivative {魏-N,N-N(C₆H₃(2-ⁱPr)CMe₂C(Me)(2-py)}₂Co (5-Co), and related thermolyses of 2-M (M = Cr, Mn, Fe), conducted on NMR tube scales, generated related 5-M (M = Cr, Mn, Fe) at roughly the same rates. This observation prompted thermolyses of (pyEA-ArRR鈥?Li, which rearrange to their corresponding indolamides in >90% yields. Rate studies, accompanied by KIE and EIE observations, revealed that an initial hydrogen transfer is reversible and is likely to correspond to an anionic rearrangement, whereas C鈥揅 bond formation is rate-determining, as suggested by accompanying calculations. X-ray structure determinations of 1, 2-Fe, 2-Co-py, 3, and 5-Co were conducted.