On the gallanyls R*Ga-3(2)center dot and R*Ga-4(3)center dot as well as gallanides R*Ga-3(2)- and R*Ga-4(3)- (R* = SitBu(3)) - Syntheses, characterization, structures

The reduction of black-blue tris(supersilyl) digallanyl [(R2Ga)-Ga-.-GaR*]( .) (R* = SitBu(3) = supersilyl) in organic solvents with Na, NaC10H8, or Na R* leads to deep-red sodium tris(supersilyl) digallanide-THF( 1/3) NaGa2R* (3)x3THF = [R*Ga-2-GaR*Na(TPIF)(3)], which transforms in the presence of 18 -crown-6 into deep-blue sodium tetrakis(supersilyl)trigallanide-18-crown-6( 1/1)-THF(1/2) [Na(18-C-6) (THF)(2)](+)-[R*Ga-2-GaR*-GaR*](-). The oxidation of the latter anion with R*Br or TCNE as well as the reaction of the digal lanyl R*Ga-3(2). with (RBr)-Br-. leads to deep-green tetra(supersilyl)cyclo trigallanyl [(...) R*Ga-GaR*(2)-GaR*(...)](-). The latter radical thermoliz es at 100 degreesC to dark-violet tetrakis(supersilyl)-tetrahedro-tetragall ane R*Ga-4(4) besides the digallanyl R*Ga-3(2)*. This is also prepared from NaR* and GaCl3 or R*3GaCl, as well as by oxidation of R*Ga-3(2)-, and itse lf thermolizes with formation of the tetrahedrane R*Ga-4(4). According to X -ray structure analyses of the mentioned compounds, the Ga-Ga bond of the d igallanide NaGa2R*(3)x3THF (NMR spectroscopically observed) is comparably s hort (2.380 Angstrom), approaching a bond order of 2. In fact, it is distin ctly shorter than the Ga-Ga bond (2.420 Angstrom) in the digallanyl R*Ga-3( 2) (EPR spectroscopically observed). The Ga atoms of the trigallanyl R*Ga-4 (3)* (EPR spectroscopically observed) are located at the corners of a trian gle with two shorter R*2Ga-GaR* sides (2.527 Angstrom) and a comparably lon ger R*Ga-GaR* basis (2.879 Angstrom). The mean value of the two Ga-Ga bonds in the trigallanide R*Ga-4(3)- (NMR spectroscopically observed) is as long (2.53 Angstrom) as the short Ga-Ga bonds in R*Ga-4(3)*. The anion shows an intramolecular (CH3Ga)-Ga-... contact (C-Ga 2.10 Angstrom) between one per ipheral methyl group of the R*Ga-2 entity and the anionic Ga atom in [R*Ga- 2-GaR*-GaR*](-).