Synthesis and Reactivity of Stable Open-Shell Gallylene

Treatment of an excess of gallium metal with iodine and 1,2-bis[(2,6-dibenzhydryl-4-methylphenyl)imino]acenaphthene (Ar^BIG-bian) in toluene at reflux affords the deep green radical [Ar^BIG-bianGaI₂] (1). Product 1 can also be synthesized by reacting Ar^BIG-bian with “GaI” in toluene. The chloride and bromide derivatives, [Ar^BIG-bianGaCl₂] (2) and [Ar^BIG-bianGaBr₂] (3), were prepared by the reactions of corresponding gallium(III) halides with Ar^BIG-bian in the presence of an excess of gallium metal in toluene. The reduction of radical 1 by potassium metal in toluene produces stable gallylene with a paramagnetic ligand [Ar^BIG-bianGa] (4). The reaction of 4 with n-propyl bromide (1:1) affords gallium(III) derivatives, 3 and [Ar^BIG-bianGaⁿPr] (5). In the course of the reaction of 4 with tetramethylthiuram disulfide (2:1), the gallium(I) center transfers two electrons: one to metallacycle and another one to the S-S bond of the substrate. The resulting product is the gallium(III) derivative [Ar^BIG-bianGaS₂CNMe₂] (6). Complexes 1-6 have been characterized by elemental analysis and IR spectroscopy, and their molecular structures have been determined by single-crystal X-ray analysis. The paramagnetic complexes 1-4 have been characterized by ESR spectroscopy and the diamagnetic compounds 5 and 6 by NMR spectroscopy. Based on DFT calculations, the electronic structures of molecules 2-5 and the thermodynamics of reactions accompanying the interaction of 4 with n-propyl bromide were studied. The computational results confirm the localization of the radical center in molecules 2-4 on the bian fragment and visualize the gallium lone pair directed along the NGaN bisector in 4. Thermodynamically favorable reactions leading to the 3 and 5 products have been identified.