Anion−π Catalysis

Article Article scientifique Article Anion−π Catalysis eng 2014 author Zhao Yingjie 757219 author Beuchat Cesar 550387 author Domoto Yuya 744959 author Gajewy Jadwiga 802297 author Wilson Adam 778574 author Mareda Jiri 24767 author Sakai Naomi 131140 author Matile Stefan 129654 2101-2111 10.1021/ja412290r 0002-7863 The introduction of new noncovalent interactions to build functional systems is of fundamental importance. We here report experimental and theoretical evidence that anion−π interactions can contribute to catalysis. The Kemp elimination is used as a classical tool to discover conceptually innovative catalysts for reactions with anionic transition states. For anion−π catalysis, a carboxylate base and a solubilizer are covalently attached to the π-acidic surface of naphthalenediimides. On these π-acidic surfaces, transition-state stabilizations up to ΔΔGTS = 31.8 ± 0.4 kJ mol–1 are found. This value corresponds to a transition-state recognition of KTS = 2.7 ± 0.5 μM and a catalytic proficiency of 3.8 × 105 M–1. Significantly increasing transition-state stabilization with increasing π-acidity of the catalyst, observed for two separate series, demonstrates the existence of “anion−π catalysis.” In sharp contrast, increasing π-acidity of the best naphthalenediimide catalysts does not influence the more than 12 000-times weaker substrate recognition (KM = 34.5 ± 1.6 μM). Together with the disappearance of Michaelis–Menten kinetics on the expanded π-surfaces of perylenediimides, this finding supports that contributions from π–π interactions are not very important for anion−π catalysis. The linker between the π-acidic surface and the carboxylate base strongly influences activity. Insufficient length and flexibility cause incompatibility with saturation kinetics. Moreover, preorganizing linkers do not improve catalysis much, suggesting that the ideal positioning of the carboxylate base on the π-acidic surface is achieved by intramolecular anion−π interactions rather than by an optimized structure of the linker. Computational simulations are in excellent agreement with experimental results. They confirm, inter alia, that the stabilization of the anionic transition states (but not the neutral ground states) increases with the π-acidity of the catalysts, i.e., the existence of anion−π catalysis. Preliminary results on the general significance of anion−π catalysis beyond the Kemp elimination are briefly discussed. Dewey 540 36 Département de chimie organique 141 false Journal of the American Chemical Society 136 5 e514306d-7e2e-4d76-bd02-932e01a28df5 Article (Published version) Restricted ja412290r.pdf 2628404 application/pdf 73fc6257-aa8d-434a-96f7-1a6d479b4924 Article (Accepted version) Public 215.pdf 1115023 application/pdf OA OTHER openAccess Faculté des sciences / Section de chimie et biochimie / Département de chimie organique

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Anion−π Catalysis	Journal of the American Chemical Society			2014	528	223

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Gajewy, Jadwiga