Scandium Ion-Promoted Reduction of Heterocyclic NN Double Bond. Hydride Transfer vs Electron Transfer
- 25 September 2002
- journal article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 124 (42), 12566-12573
- https://doi.org/10.1021/ja026592y
Abstract
Hydride transfer from 10-methyl-9,10-dihydroacridine (AcrH2) to 3,6-diphenyl-1,2,4,5-tetrazine (Ph2Tz), which contains a NN double bond, occurs efficiently in the presence of Sc(OTf)3 (OTf = OSO2CF3) in deaerated acetonitrile (MeCN) at 298 K, whereas no reaction occurs in the absence of Sc3+. The observed second-order rate constant (kobs) increases with increasing Sc3+ concentration to approach a limited value. When AcrH2 is replaced by the dideuterated compound (AcrD2), the rate of Sc3+-promoted hydride transfer exhibits the same primary kinetic isotope effect (kH/kD = 5.2±0.2), irrespective of Sc3+ concentration. Scandium ion also promotes an electron transfer from CoTPP (TPP2- = tetraphenylporphyrin dianion) and 10,10‘-dimethyl-9,9‘-biacridine [(AcrH)2] to Ph2Tz, whereas no electron transfer from CoTPP or (AcrH)2 to Ph2Tz occurs in the absence of Sc3+. In each case, the observed second-order rate constant of electron transfer (ket) shows a first-order dependence on [Sc3+] at low concentrations and a second-order dependence at higher concentrations. Such dependence of ket on [Sc3+] is ascribed to formation of 1:1 and 1:2 complexes between Ph2Tz•- and Sc3+ at the low and high concentrations of Sc3+, respectively, which results in acceleration of the rate of electron transfer. The formation of 1:2 complex has been confirmed by the ESR spectrum in which the hyperfine structure is different from that of free Ph2Tz•-. The 1:2 complex formation results in the saturated kinetic dependence of kobs on [Sc3+] for the Sc3+-promoted hydride transfer, which proceeds via Sc3+-promoted electron transfer from AcrH2 to Ph2Tz, followed by proton transfer from AcrH2•+ to the 1:1 Ph2Tz•-−Sc3+ complex and the subsequent facile electron transfer from AcrH• to Ph2TzH•. The effects of counteranions on the Sc3+-promoted electron transfer and hydride transfer reactions are also reported.Keywords
This publication has 98 references indexed in Scilit:
- An One-Pot Synthesis of Semibullvalenes and Its MechanismEuropean Journal of Organic Chemistry, 2002
- Metal Ion-Catalyzed Cycloaddition vs Hydride Transfer Reactions of NADH Analogues with p-BenzoquinonesJournal of the American Chemical Society, 2001
- 3,6-Bis(2H-tetrazol-5-yl)-1,2,4,5-tetrazine: A Versatile Bifunctional Building Block for the Synthesis of Linear OligoheterocyclesEuropean Journal of Organic Chemistry, 2001
- Electrochemical Behavior and Characterization of Semiquinone Radical Anion Species of Coenzyme PQQ in Aprotic Organic MediaJournal of the American Chemical Society, 1998
- The Role of Homolytic Bond Dissociation Energy in the Deprotonation of Cation Radicals. Examples in the NADH Analogues SeriesJournal of the American Chemical Society, 1998
- A New Methodology for Combinatorial Synthesis. Preparation of Diverse Quinoline Derivatives Using a Novel Polymer-Supported Scandium CatalystJournal of the American Chemical Society, 1996
- A Polymer-Supported Scandium CatalystThe Journal of Organic Chemistry, 1996
- Ln(OTf)3–LiClO4as reusable catalyst system for Friedel–Crafts acylationChemical Communications, 1996
- A Chiral Scandium Catalyst for Enantioselective Diels-Alder ReactionsThe Journal of Organic Chemistry, 1994
- Outer-sphere electron-transfer oxidation of 10,10'-dimethyl-9,9',10,10'-tetrahydro-9,9'-biacridineThe Journal of Physical Chemistry, 1992