Magnesium(I)-Mediated Dearomatizing Coupling of Pyridines and Subsequent Hydrogen Transfer Reactions

The Mg─Mg-bonded compound [K(THF)₃]₂[LMg─MgL]₂ (1, L = [(2,6-iPr₂C₆H₃)NC(CH₃)]₂²⁻) can promote reductive 4,4′-homocoupling of pyridine and derivatives under ambient conditions, yielding the 4,4′-dihydro-4,4′-bipyridinate products 2–6. Interestingly, these species can be viewed as “dimerized” metal-1,4-dihydropyridinates (bis-M-DHPs) and can transfer hydrogen or deuterium (as proton and hydride) to pyridines, imines and alkenes. This may provide a facile access to new H/D-donors, readily obtained from commercially available pyridines and a conveniently synthesized magnesium(I) complex, for controllable H-transfer (HT) to different types of unsaturated molecules. The coupling and HT mechanisms were elucidated by DFT calculations.