Reactivity of Low Valent Magnesium(I) Complexes with Epoxides and Episulfides

Abstract

Abstract Chemical C–H functionalisation is traditionally the domain of potent organolithium bases that require cryogenic conditions, whereas biologically inspired C–H functionalisation can be executed by transition metal‐oxo species. Blending these chemical and biological approaches, this work exploits magnesium‐oxo complexes for selective C–H deprotonation at ambient temperature. Overall, three low valent magnesium(I) dimers, [ Dipp NacnacMg] 2 1 , [ Dep NacnacMg] 2 2 and [ Mes NacnacMg] 2 3 , react with two equivalents of propylene oxide to generate dinuclear Mg complexes of general formula [NacnacMg(OH)(OCH 2 CHCH 2 )MgNacnac] (Nacnac = HC(C(CH 3 )NAr) 2 ). Isolation of oxo‐bridged [ Dipp NacnacMg‐O‐Mg Dipp Nacnac] coupled with deuterium labeling studies shows that the reaction proceeds via epoxide deoxygenation, followed by deprotonation and rearrangement of a second equivalent of the epoxide to generate the alkoxide. A range of terminal and internal epoxides was investigated (propylene oxide, butylene oxide, isobutylene oxide, and cyclohexene oxide). The β‐C‐H position was selectively deprotonated in each case, as confirmed by NMR spectroscopy and X‐ray diffraction studies. Exchanging epoxides for episulfides instead generated disulfide‐bridged species, showcasing the difference in Brønsted basicity between Mg‐O and Mg‐S functional groups. Overall, this work demonstrates the unharnessed potential of main group metal‐oxo complexes for selective C–H deprotonation.