Unexpected transformations of an allyl group in a gallium complex with the redox-active dpp-bian ligand

The complex [(dpp-bian) − Ga(σ-allyl)Cl] ( 1 ), which was prepared by the oxidative addition of two equivalents of allyl chloride to digallane [(dpp-bian) 2− Ga—Ga(dpp-bian) 2− ], reacts with one equivalent of sodium in tetrahydrofuran (THF) at 40 °C to afford the complex [(dpp-bian) 2− (THF)Ga] 2 (µ 2 -1,3-C 3 H 6 ) ( 2 ), in which two gallium atoms are connected by the bridging propane-1,3-diyl moiety. Under more harsh conditions (80 °C), this reaction gives asymmetric anionic digallane [(dpp-bian)Ga—Ga(dpp-bian)(σ-C 9 H 13 )] − ( 3 ) with the [Na(Et 2 O) 3 (THF)] + cation as the counterion. The σ-H 13 moiety in digallane 3 resulted from the cyclotrimerization of three allyl radicals. Compounds 2 and 3 were characterized by IR spectroscopy, multinuclear NMR spectroscopy, and elemental analysis. Their molecular structures were determined by single-crystal X-ray diffraction. Compounds 2 and 3 are unique because they contain the previously unknown metal fragments M—CH 2 CH 2 CH 2 —M and σ-C 9 H 13 —M, respectively. It is suggested that these complexes are produced via cascade β-elimination, carbo- and hydrogallation reactions.