Synthesis of Magnesium Complexes of 2-Butene-1,4-diyl by Reduction of Dienes with a Mg-Mg-Bonded Compound

Reactions of the dimagnesium(I) complex [K(THF)₃]₂[LMg-MgL] (1, L = [(2,6-iPr₂C₆H₃)NC(CH₃)]₂^2-) with a series of conjugated dienes, including 1,3-butadiene and its derivatives, 3-methyl-1,3-pentadiene, and 2,4-hexadiene, led to the reduction of the diene moiety to the 2-butene-1,4-diyl dianion. Bimetallic (Mg/K) complexes (2-6) of this dicarbanion were obtained, in which two Mg(II) centers are bridged by the butenediyl fragment through σ¹-bonding to the carbanions, while two K⁺ ions are each η³-bonded by an “allyl” group of the butenediyl. Moreover, complex 7, containing a (Z,Z)-hexadienyl bridge, was also isolated upon the double dehydrogenation of hexadiene. The products were characterized by ¹H and ¹³C NMR, UV-vis spectroscopy, and single-crystal X-ray diffraction. The work demonstrates the promising reactivity of the dimagnesium(I) complex as an electron donor and provides possible access to bis(Grignard) reagents.