Photochemically Activated Dimagnesium(I) Compounds: Reagents for the Reduction and Selective C−H Bond Activation of Inert Arenes

The photochemical activation of dimagnesium(I) compounds, and subsequent high yielding, regioselective reactions with inert arenes are reported. Irradiating benzene solutions of [{( Ar Nacnac)Mg} 2 ] ( Ar Nacnac=[HC(MeCNAr) 2 ] − ; Ar=2,6‐diisopropylphenyl (Dip) or 2,4,6‐tricyclohexylphenyl (TCHP)) with blue or UV light, leads to double reduction of benzene and formation of the “Birch‐like” cyclohexadienediyl bridged compounds, [{( Ar Nacnac)Mg} 2 (μ‐C 6 H 6 )]. Irradiation of [{( Dip Nacnac)Mg} 2 ] in toluene, and each of the three isomers of xylene, promoted completely regio‐ and chemo‐selective C−H bond activations, and formation of [( Dip Nacnac)Mg(Ar′)] (Ar′= meta ‐tolyl; 2,3‐, 3,5‐ or 2,5‐dimethylphenyl), and [{( Dip Nacnac)Mg(μ‐H)} 2 ]. Fluorobenzene was cleanly defluorinated by photoactivated [{( Dip Nacnac)Mg} 2 ], leading to biphenyl and [{( Dip Nacnac)Mg(μ‐F)} 2 ]. Computational studies suggest all reactions proceed via photochemically generated magnesium(I) radicals, which reduce the arene substrate, before C−H or C−F bond activation processes occur.