Alkali-metal-mediated magnesiations of an N-heterocyclic carbene : normal, abnormal and "paranormal" reactivity in a single tritopic molecule

Martínez-Martínez, Antonio J. and Fuentes, M. Ángeles and Hernán-Gõmez, Alberto and Hevia, Eva and Kennedy, Alan R. and Mulvey, Robert E. and O'Hara, Charles T. (2015) Alkali-metal-mediated magnesiations of an N-heterocyclic carbene : normal, abnormal and "paranormal" reactivity in a single tritopic molecule. Angewandte Chemie International Edition, 54 (47). pp. 14075-14079. ISSN 1433-7851

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    Abstract

    Herein the sodium alkylmagnesium amide [Na4Mg2(TMP)6(nBu)2] (TMP=2,2,6,6-tetramethylpiperidide), a template base as its deprotonating action is dictated primarily by its 12 atom ring structure, is studied with the common N-heterocyclic carbene (NHC) IPr [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene]. Remarkably, magnesiation of IPr occurs at the para-position of an aryl substituent, sodiation occurs at the abnormal C4 position, and a dative bond occurs between normal C2 and sodium, all within a 20 atom ring structure accommodating two IPr2-. Studies with different K/Mg and Na/Mg bimetallic bases led to two other magnesiated NHC structures containing two or three IPr- monoanions bound to Mg through abnormal C4 sites. Synergistic in that magnesiation can only work through alkali-metal mediation, these reactions add magnesium to the small cartel of metals capable of directly metalating a NHC.