Pyrazole-Based PCN Pincer Complexes of Palladium(II): Mono- and Dinuclear Hydroxide Complexes and Ligand Rollover C鈥揌 Activation

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• 作者：Wilson D. Bailey ; Lapo Luconi ; Andrea Rossin ; Dmitry Yakhvarov ; Sarah E. Flowers ; Werner Kaminsky ; Richard A. Kemp ; Giuliano Giambastiani ; Karen I. Goldberg
• 刊名：Organometallics
• 出版年：2015
• 出版时间：August 24, 2015
• 年：2015
• 卷：34
• 期：16
• 页码：3998-4010
• 全文大小：645K
• ISSN：1520-6041

文摘

Palladium complexes of the novel unsymmetrical phosphine pyrazole-containing pincer ligands PCN^H (PCN^H = 1-[3-[(di-tert-butylphosphino)methyl]phenyl]-1H-pyrazole) and PCN^Me (PCN^Me = 1-[3-[(di-tert-butylphosphino)methyl]phenyl]-5-methyl-1H-pyrazole) have been prepared and characterized through single-crystal X-ray diffraction and multinuclear ¹H, ¹³C{¹H}, and ³¹P{¹H} NMR spectroscopy. In preparations of the monomeric hydroxide species (PCN^H)Pd(OH), an unexpected N detachment followed by C鈥揌 activation on the heterocycle 5-position took place resulting in conversion of the monoanionic {P,C^{鈥?/sup>,N} framework into a dianionic {P,C鈥?/sup>,C鈥?/sup>} ligand set. The dinuclear hydroxide-bridged species (PCNH)Pd(渭-OH)Pd(PCC) was the final product obtained under ambient conditions. The 鈥渞ollover鈥?activation was followed via 31P{1H} NMR spectroscopy, and dinuclear cationic 渭-OH and monomeric PdII hydroxide intermediates were identified. DFT computational analysis of the process (M06//6-31G*, THF) showed that the energy barriers for the pyrazolyl rollover and for C鈥揌 activation through a 蟽-bond metathesis reaction are low enough to be overcome under ambient-temperature conditions, in line with the experimental findings. In contrast to the PCNH system, no 鈥渞ollover鈥?reactivity was observed in the PCNMe system, and the terminal hydroxide complex (PCNMe)Pd(OH) could be readily isolated and fully characterized.}