TY - JOUR
T1 - Pyrazole-Based PCN Pincer Complexes of Palladium(II)
T2 - Mono- and Dinuclear Hydroxide Complexes and Ligand Rollover C-H Activation
AU - Bailey, Wilson D.
AU - Luconi, Lapo
AU - Rossin, Andrea
AU - Yakhvarov, Dmitry
AU - Flowers, Sarah E.
AU - Kaminsky, Werner
AU - Kemp, Richard A.
AU - Giambastiani, Giuliano
AU - Goldberg, Karen I.
N1 - Publisher Copyright:
© 2015 American Chemical Society.
PY - 2015/8/24
Y1 - 2015/8/24
N2 - Palladium complexes of the novel unsymmetrical phosphine pyrazole-containing pincer ligands PCNH (PCNH = 1-[3-[(di-tert-butylphosphino)methyl]phenyl]-1H-pyrazole) and PCNMe (PCNMe = 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 (PCNH)Pd(OH), an unexpected N detachment followed by C-H activation on the heterocycle 5-position took place resulting in conversion of the monoanionic {P,C-,N} framework into a dianionic {P,C-,C-} ligand set. The dinuclear hydroxide-bridged species (PCNH)Pd(μ-OH)Pd(PCC) was the final product obtained under ambient conditions. The "rollover" activation was followed via 31P{1H} NMR spectroscopy, and dinuclear cationic μ-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-H activation through a σ-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 "rollover" reactivity was observed in the PCNMe system, and the terminal hydroxide complex (PCNMe)Pd(OH) could be readily isolated and fully characterized. (Chemical Equation Presented).
AB - Palladium complexes of the novel unsymmetrical phosphine pyrazole-containing pincer ligands PCNH (PCNH = 1-[3-[(di-tert-butylphosphino)methyl]phenyl]-1H-pyrazole) and PCNMe (PCNMe = 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 (PCNH)Pd(OH), an unexpected N detachment followed by C-H activation on the heterocycle 5-position took place resulting in conversion of the monoanionic {P,C-,N} framework into a dianionic {P,C-,C-} ligand set. The dinuclear hydroxide-bridged species (PCNH)Pd(μ-OH)Pd(PCC) was the final product obtained under ambient conditions. The "rollover" activation was followed via 31P{1H} NMR spectroscopy, and dinuclear cationic μ-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-H activation through a σ-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 "rollover" reactivity was observed in the PCNMe system, and the terminal hydroxide complex (PCNMe)Pd(OH) could be readily isolated and fully characterized. (Chemical Equation Presented).
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U2 - 10.1021/acs.organomet.5b00355
DO - 10.1021/acs.organomet.5b00355
M3 - Article
AN - SCOPUS:84940213856
SN - 0276-7333
VL - 34
SP - 3998
EP - 4010
JO - Organometallics
JF - Organometallics
IS - 16
ER -