Tri(supersilyl)dialanyl (tBu3Si)3Al2• and Tetra(supersilyl)cyclotrialanyl (tBu3Si)4Al3• − New Stable Radicals of a Group 13 Element from Thermolysis of (tBu3Si)4Al2

Abstract

The thermolysis of tetra(supersilyl)dialane R*2Al−AlR*2 (R* = SitBu3 = Supersilyl) in heptane or cyclohexane at 50 °C leads under Al−Al dissociation reversibly to monoalanyl radicals [R*2Al]•, which could be trapped by hydrogen or iodine (formation of R*2AlH, R*2AlI). Simultaneously, SiAl dissociation and elimination of supersilyl radicals tBu3Si• leads irreversibly and slowly to radicals [R*2Al−AlR*]•, the existence of which could be established by ESR spectroscopy. The structure was clarified by ab initio calculations (nearly planar Si2Al−AlSi and linear Al−Al−Si skeleton; short Al−Al distance). By thermolyzing R*2Al−AlR*2 at 100 °C, the radical [R*4Al3]• (ESR spectroscopically detected) and the tetrahedro-tetraalane R*4Al4 (NMR spectroscopically seen) are formed via radicals [R*3Al2]•; the supersilyl radicals tBu3Si•, formed at the same time, are stabilized by dimerization to superdisilane R*−R* and by taking up hydrogen, giving supersilane R*−H. According to X-ray structure analysis, the Al atoms in [R*4Al3]• are located at the corners of a triangle; one Al atom is connected with two groups R*, the remaining two Al atoms each bind one substituent R* in different ways.