Ligand “Brackets” for Ga–Ga Bond

The reactivity of digallane (dpp-Bian)­Ga–Ga­(dpp-Bian)
(1) (dpp-Bian = 1,2-bis­[(2,6-diisopropylphenyl)­imino]­acenaphthene)
toward acenaphthenequinone (AcQ), sulfur dioxide, and azobenzene was
investigated. The reaction of 1 with AcQ in 1:1 molar
ratio proceeds via two-electron reduction of AcQ to give (dpp-Bian)­Ga­(μ2-AcQ)­Ga­(dpp-Bian) (2), in which diolate [AcQ]2– acts as “bracket” for the Ga–Ga
bond. The interaction of 1 with AcQ in 1:2 molar ratio
proceeds with an oxidation of the both dpp-Bian ligands as well as
of the Ga–Ga bond to give (dpp-Bian)­Ga­(μ2-AcQ)2Ga­(dpp-Bian) (3). At 330 K in
toluene complex 2 decomposes to give compounds 3 and 1. The reaction of complex 2 with atmospheric oxygen results in oxidation of a Ga–Ga bond
and affords (dpp-Bian)­Ga­(μ2-AcQ)­(μ2-O)­Ga­(dpp-Bian) (4). The reaction of digallane 1 with SO2 produces, depending on the ratio (1:2
or 1:4), dithionites (dpp-Bian)­Ga­(μ2-O2S–SO2)­Ga­(dpp-Bian) (5) and
(dpp-Bian)­Ga­(μ2-O2S–SO2)2Ga­(dpp-Bian) (6). In compound 5 the Ga–Ga bond is preserved and supported by dithionite
dianionic bracket. In compound 6 the gallium centers
are bridged by two dithionite ligands. Both 5 and 6 consist of dpp-Bian radical anionic ligands. Four-electron
reduction of azobenzene with 1 mol equiv of digallane 1 leads to complex (dpp-Bian)­Ga­(μ2-NPh)2Ga­(dpp-Bian) (7). Paramagnetic compounds 2–7 were characterized by electron spin
resonance spectroscopy, and their molecular structures were established
by single-crystal X-ray analysis. Magnetic behavior of compounds 2, 5, and 6 was investigated by
superconducting quantum interference device technique in the range
of 2–295 K.