Protic N-Heterocyclic Carbene Versus Pyrazole: Rigorous Comparison of Proton- and Electron-Donating Abilities in a Pincer-Type Framework.
作者： Tatsuro Toda , Akihiro Yoshinari , Takao Ikariya , Shigeki Kuwata
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摘要: Evaluation of the acidity proton-responsive ligands such as protic N-heterocyclic carbenes (NHCs) bearing an NH-wingtip provides a key to understanding metal-ligand cooperation in enzymatic and artificial catalysis. Here, we design CNN pincer-type ruthenium complex 2 NHC isoelectronic pyrazole units symmetrical skeleton, compare their acidities electron-donating abilities. The synthesis is achieved by direct C-H metalation 2-(imidazol-1-yl)-6-(pyrazol-3-yl)pyridine with [RuCl2 (PPh3 )3 ]. 15 N-Labeling experiments confirm that deprotonation occurs first at side, indicating clearly more acidic than group. electrochemical measurements well derivatization carbonyl complexes demonstrate both protonated deprotonated forms.
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