Synthesis and Reactivity of Stable Open-Shell Gallylene

Abstract

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.